D
DDFT - deep digital flexor tendon/tenotomy
Deep Digital Flexor Muscle
Dexamethasone Suppression Test
Diabetes
Diet
Digital pulse
Distal descent/sinking
Domperidone
Donkeys and mules
Dopamine (DA)
Dopamine agonists
Deep Digital Flexor Muscle
Dexamethasone Suppression Test
Diabetes
Diet
Digital pulse
Distal descent/sinking
Domperidone
Donkeys and mules
Dopamine (DA)
Dopamine agonists
DDFT - deep digital flexor tendon/tenotomy
DDFT - what is it?
The deep digital flexor tendon (DDFT) runs from the deep digital flexor muscle (between the elbow and the knee), behind the knee, along the back of the cannon bone, the back of the fetlock, around the back of the navicular bone and inserts on the palmer (back) aspect/undersurface of the coffin/pedal bone. See (DDFT at approx. 2:50 mins):
Equine distal forelimb: tendons and ligaments
(see also: Anatomy)
Does tension in the DDFT (or deep digital flexor muscle) contribute to laminitis?
It has been suggested that the DDFT exerts a force on the coffin/pedal bone, so that when laminar connections at the toe are weakened or destroyed by laminitis, the pull of the DDFT is what causes the coffin/pedal bone to rotate. However this doesn't appear to explain why the coffin/pedal bones of horses with damage to the laminae all round the foot sink with the bone usually remaining parallel to the ground and in alignment with P1 and P2.
The pull of the deep flexor tendon - John Stewart
"I believe that the weight of the horse on the pedal bone is more important than the pull of the deep flexor tendon so that it is more important to trim the feet of chronic founder cases with a ground-parallel pedal bone and that raising the heel to decrease the tension in the DFT is more likely to lead to continuation of the distortion and instability in the feet. The toe must always be taken back to allow breakover without pulling the dorsal wall away from the pedal bone."
Ramsey GD, Hunter PJ, Nash MP
The effect of hoof angle variations on dorsal lamellar load in the equine hoof
Equine Vet J. 2011 Sep;43(5):536-4.2 E pub: 11 Mar 2011
"CONCLUSIONS AND POTENTIAL RELEVANCE: The models in this study predict that raising the palmar angle increases the load on the dorsal laminar junction. Therefore, hoof care interventions that raise the palmar angle in order to reduce the dorsal lamellae load may not achieve this outcome."
McGuigan MP, Walsh TC, Pardoe CH, Day PS, Wilson AM
Deep digital flexor tendon force and digital mechanics in normal ponies and ponies with rotation of the distal phalanx as a sequel to laminitis
Equine Vet J. 2005 Mar;37(2):161-5 (PubMed)
"Reasons for performing study: Previous studies have implicated tension in the deep digital flexor tendon (DDFT) in the rotation of the distal phalanx (DP) after the breakdown of the dorsal laminae caused by laminitis. However, once the DP has rotated, the DDFT should become shorter, reducing the force it exerts on the DP."
"Conclusions: DDFT force in Group 2 laminitic ponies was much reduced until late stance, when it neared normal values."
Excessive Deep Digital Flexor Tendon (DDFT) Tension - South Shore Equine Clinic & Diagnostic Centre
Raising the heel, and in extreme cases, cutting the DDFT (a procedure called tenotomy), supposedly to reduce tension in the DDFT and prevent or realign rotation of the coffin/pedal bone, is recommended by some and condemned by others.
Could it be that raising the heels long-term, or not trimming the horse's heels to achieve a (near) ground parallel solar aspect of the coffin/pedal bone (i.e. not realigning rotation) at the earliest opportunity, allows the DDFT to contract? So that it is perhaps an effect of rotation rather than a cause?
Rapid improvement of cases of laminitis with rotation and/or sinking is often reported on the ECIRGroup (and sister group ECHoof) following frequent trimming to shorten the toe and lower the heel, thereby restoring alignment of the hoof to P3 at the earliest opportunity - see DDT- Trim
Coffin Bone Rotation explained the natural way - Swedish Hoof School
Deep digital flexor tenotomy (surgically cutting the DDFT)
In some cases of laminitis, surgically cutting the deep digital flexor tendon is recommended. It is important before carrying out this surgery that correct realigning trimming and support has been carried out.
DDFT tenotomy
Saratogy Lecture - shows examples of DDF tenotomy
Journal of Equine Veterinary Science, Volume 31, Issue 2, February 2011, Pages 89-96
Long-term Prognosis Using Deep Digital Flexor Tenotomy and Realignment Shoeing for Treatment of Chronic Laminitis
Morrison S
J Am Vet Med Assoc 1999 Feb 15;214(4):517-9. Erratum in J Am Vet Med Assoc 1999 April 15;214(8):1217 (PubMed)
Deep digital flexor tenotomy as a treatment for chronic laminitis in horses: 35 cases (1988-1997)
Eastman T, Honnas C, Hague B, Moyer W, von der Rosen H
Abstract OBJECTIVE: To determine long-term prognosis for horses with laminitis treated by deep digital flexor (DDF) tenotomy and to identify factors affecting success of the surgical procedure.
DESIGN: Retrospective study.
ANIMALS: 35 horses with laminitis treated by DDF tenotomy between 1988 and 1997.
PROCEDURE: Information was obtained from individual medical records and follow-up telephone interviews with owners and referring veterinarians. Cumulative proportions of horses that survived 6 months and 2 years after tenotomy were determined. Effect of Obel grade of lameness on 6-month and 2-year survival and effect of distal phalangeal rotation on survival and future performance were evaluated by chi 2 analysis. Body weights of horses that survived > or = 2 years were compared with those of horses that survived < 2 years by ANOVA.
RESULTS: 27 of the 35 (77%) horses survived > or = 6 months, and 19 of 32 (59%) survived > 2 years. Obel grade of lameness and body weight at time of surgery had no effect on 6-month or 2-year survival. Degree of distal phalangeal rotation had no effect on 2-year survival or the ability of horses to be used for light riding. Twenty-two of the 30 (73%) owners interviewed indicated they would have the procedure repeated on their horses given similar circumstances.
CLINICAL IMPLICATIONS: DDF tenotomy is a viable alternative for horses with laminitis refractory to conventional medical treatment. In some instances, the procedure may be effective in returning horses to light athletic use.
Factors involved in the prognosis of laminitis in the UK
Eustace R, Cripps P
Vet Surg 1991 Jan-Feb;20(1):15-20. (PubMed)
Mid-metacarpal deep digital flexor tenotomy in the management of refractory laminitis in horses
Hunt R, Allen D, Baxter G, Jackman B, Parks A
"Deep digital flexor tendon transection at the mid-metacarpus was performed in 20 horses with severe acute or chronic laminitis that was not responsive to conventional treatment. Sixteen horses improved within 72 hours, one horse worsened, and two horses were unaffected by the surgery. Eleven horses survived less than 1 month after surgery and six horses survived longer than 6 months. Three horses surviving longer than 6 months have remained lame and no horse has returned to athletic performance. Transection of the deep digital flexor tendon at the mid-metacarpus may decrease the pain associated with the acute refractory stage of laminitis and may be useful as an immediate salvage procedure; however, despite the early clinical improvement observed after tenotomy, the survival rate of affected horses may not be altered."
J Am Vet Med Assoc 1986 Dec 15;189(12):1604-6. (PubMed)
Surgical management of chronic laminitis in horses: 13 cases (1983-1985)
Allen D, White N, Foerner J, Gordon B
"Thirteen horses with chronic refractory laminitis were evaluated and treated. In each horse, deep digital flexor tenotomy was performed on all affected limbs at the level of the midpastern. Five horses returned to limited athletic endeavors, 6 horses improved and were comfortable on pasture, 1 horse improved clinically, but was euthanatized for economic reasons, and 1 horse improved, but deteriorated 9 months after surgery and was euthanatized. Results of this study indicated that deep digital flexor tenotomy at the level of the midpastern can be used effectively as a salvage procedure in horses with chronic refractory laminitis."
The deep digital flexor tendon (DDFT) runs from the deep digital flexor muscle (between the elbow and the knee), behind the knee, along the back of the cannon bone, the back of the fetlock, around the back of the navicular bone and inserts on the palmer (back) aspect/undersurface of the coffin/pedal bone. See (DDFT at approx. 2:50 mins):
Equine distal forelimb: tendons and ligaments
(see also: Anatomy)
Does tension in the DDFT (or deep digital flexor muscle) contribute to laminitis?
It has been suggested that the DDFT exerts a force on the coffin/pedal bone, so that when laminar connections at the toe are weakened or destroyed by laminitis, the pull of the DDFT is what causes the coffin/pedal bone to rotate. However this doesn't appear to explain why the coffin/pedal bones of horses with damage to the laminae all round the foot sink with the bone usually remaining parallel to the ground and in alignment with P1 and P2.
The pull of the deep flexor tendon - John Stewart
"I believe that the weight of the horse on the pedal bone is more important than the pull of the deep flexor tendon so that it is more important to trim the feet of chronic founder cases with a ground-parallel pedal bone and that raising the heel to decrease the tension in the DFT is more likely to lead to continuation of the distortion and instability in the feet. The toe must always be taken back to allow breakover without pulling the dorsal wall away from the pedal bone."
Ramsey GD, Hunter PJ, Nash MP
The effect of hoof angle variations on dorsal lamellar load in the equine hoof
Equine Vet J. 2011 Sep;43(5):536-4.2 E pub: 11 Mar 2011
"CONCLUSIONS AND POTENTIAL RELEVANCE: The models in this study predict that raising the palmar angle increases the load on the dorsal laminar junction. Therefore, hoof care interventions that raise the palmar angle in order to reduce the dorsal lamellae load may not achieve this outcome."
McGuigan MP, Walsh TC, Pardoe CH, Day PS, Wilson AM
Deep digital flexor tendon force and digital mechanics in normal ponies and ponies with rotation of the distal phalanx as a sequel to laminitis
Equine Vet J. 2005 Mar;37(2):161-5 (PubMed)
"Reasons for performing study: Previous studies have implicated tension in the deep digital flexor tendon (DDFT) in the rotation of the distal phalanx (DP) after the breakdown of the dorsal laminae caused by laminitis. However, once the DP has rotated, the DDFT should become shorter, reducing the force it exerts on the DP."
"Conclusions: DDFT force in Group 2 laminitic ponies was much reduced until late stance, when it neared normal values."
Excessive Deep Digital Flexor Tendon (DDFT) Tension - South Shore Equine Clinic & Diagnostic Centre
Raising the heel, and in extreme cases, cutting the DDFT (a procedure called tenotomy), supposedly to reduce tension in the DDFT and prevent or realign rotation of the coffin/pedal bone, is recommended by some and condemned by others.
Could it be that raising the heels long-term, or not trimming the horse's heels to achieve a (near) ground parallel solar aspect of the coffin/pedal bone (i.e. not realigning rotation) at the earliest opportunity, allows the DDFT to contract? So that it is perhaps an effect of rotation rather than a cause?
Rapid improvement of cases of laminitis with rotation and/or sinking is often reported on the ECIRGroup (and sister group ECHoof) following frequent trimming to shorten the toe and lower the heel, thereby restoring alignment of the hoof to P3 at the earliest opportunity - see DDT- Trim
Coffin Bone Rotation explained the natural way - Swedish Hoof School
Deep digital flexor tenotomy (surgically cutting the DDFT)
In some cases of laminitis, surgically cutting the deep digital flexor tendon is recommended. It is important before carrying out this surgery that correct realigning trimming and support has been carried out.
DDFT tenotomy
Saratogy Lecture - shows examples of DDF tenotomy
Journal of Equine Veterinary Science, Volume 31, Issue 2, February 2011, Pages 89-96
Long-term Prognosis Using Deep Digital Flexor Tenotomy and Realignment Shoeing for Treatment of Chronic Laminitis
Morrison S
J Am Vet Med Assoc 1999 Feb 15;214(4):517-9. Erratum in J Am Vet Med Assoc 1999 April 15;214(8):1217 (PubMed)
Deep digital flexor tenotomy as a treatment for chronic laminitis in horses: 35 cases (1988-1997)
Eastman T, Honnas C, Hague B, Moyer W, von der Rosen H
Abstract OBJECTIVE: To determine long-term prognosis for horses with laminitis treated by deep digital flexor (DDF) tenotomy and to identify factors affecting success of the surgical procedure.
DESIGN: Retrospective study.
ANIMALS: 35 horses with laminitis treated by DDF tenotomy between 1988 and 1997.
PROCEDURE: Information was obtained from individual medical records and follow-up telephone interviews with owners and referring veterinarians. Cumulative proportions of horses that survived 6 months and 2 years after tenotomy were determined. Effect of Obel grade of lameness on 6-month and 2-year survival and effect of distal phalangeal rotation on survival and future performance were evaluated by chi 2 analysis. Body weights of horses that survived > or = 2 years were compared with those of horses that survived < 2 years by ANOVA.
RESULTS: 27 of the 35 (77%) horses survived > or = 6 months, and 19 of 32 (59%) survived > 2 years. Obel grade of lameness and body weight at time of surgery had no effect on 6-month or 2-year survival. Degree of distal phalangeal rotation had no effect on 2-year survival or the ability of horses to be used for light riding. Twenty-two of the 30 (73%) owners interviewed indicated they would have the procedure repeated on their horses given similar circumstances.
CLINICAL IMPLICATIONS: DDF tenotomy is a viable alternative for horses with laminitis refractory to conventional medical treatment. In some instances, the procedure may be effective in returning horses to light athletic use.
Factors involved in the prognosis of laminitis in the UK
Eustace R, Cripps P
Vet Surg 1991 Jan-Feb;20(1):15-20. (PubMed)
Mid-metacarpal deep digital flexor tenotomy in the management of refractory laminitis in horses
Hunt R, Allen D, Baxter G, Jackman B, Parks A
"Deep digital flexor tendon transection at the mid-metacarpus was performed in 20 horses with severe acute or chronic laminitis that was not responsive to conventional treatment. Sixteen horses improved within 72 hours, one horse worsened, and two horses were unaffected by the surgery. Eleven horses survived less than 1 month after surgery and six horses survived longer than 6 months. Three horses surviving longer than 6 months have remained lame and no horse has returned to athletic performance. Transection of the deep digital flexor tendon at the mid-metacarpus may decrease the pain associated with the acute refractory stage of laminitis and may be useful as an immediate salvage procedure; however, despite the early clinical improvement observed after tenotomy, the survival rate of affected horses may not be altered."
J Am Vet Med Assoc 1986 Dec 15;189(12):1604-6. (PubMed)
Surgical management of chronic laminitis in horses: 13 cases (1983-1985)
Allen D, White N, Foerner J, Gordon B
"Thirteen horses with chronic refractory laminitis were evaluated and treated. In each horse, deep digital flexor tenotomy was performed on all affected limbs at the level of the midpastern. Five horses returned to limited athletic endeavors, 6 horses improved and were comfortable on pasture, 1 horse improved clinically, but was euthanatized for economic reasons, and 1 horse improved, but deteriorated 9 months after surgery and was euthanatized. Results of this study indicated that deep digital flexor tenotomy at the level of the midpastern can be used effectively as a salvage procedure in horses with chronic refractory laminitis."
Deep Digital Flexor Muscle
Massaging the deep digital flexor muscle may be of benefit to horses with laminitis, particularly before/after realigning trimming to lower heels, and may help prevent/reduce tension in the deep digital flexor tendon.
Diagram showing the position of the digital flexor muscle:
The Journal of Experimental Biology 206, 1325-1336, 2003
The effect of gait and digital flexor muscle activation on limb compliance in the forelimb of the horse Equus caballus
M. Polly McGuigan and Alan M. Wilson
Hardeman LC, van der Meij BR, Back W, van der Kolk JH, Wijnberg ID
The use of electromyography including interference pattern analysis to determine muscle force of the deep digital flexor muscle in case of equine laminitis
BEVA Sept 2015 p 253
Diagram showing the position of the digital flexor muscle:
The Journal of Experimental Biology 206, 1325-1336, 2003
The effect of gait and digital flexor muscle activation on limb compliance in the forelimb of the horse Equus caballus
M. Polly McGuigan and Alan M. Wilson
Hardeman LC, van der Meij BR, Back W, van der Kolk JH, Wijnberg ID
The use of electromyography including interference pattern analysis to determine muscle force of the deep digital flexor muscle in case of equine laminitis
BEVA Sept 2015 p 253
Dexamethasone suppression test (DST/ODST)
THIS TEST SHOULD NO LONGER BE USED FOR DIAGNOSING PPID AND MAY INCREASE THE RISK OF LAMINITIS
See also Combined Dexamethasone Suppression/TRH stimulation test.
The dexamethasone suppression test (DST) was once considered the "gold standard" method of diagnosing PPID. However, this appears to have been based on research by Dybdal et al. published in 1994, which is now considered to have been "favourably biased" (see below). The resting ACTH blood test is now the test of choice for diagnosing PPID, has several advantages over the DST, and is the test recommended by The Laminitis Site.
The DST (sometimes called Overnight DST) involves collecting blood to test baseline cortisol in the late afternoon, then injecting 40μg/kg dexamethasone (20 mg/500 kg horse), then collecting a second blood sample to test cortisol the following morning, approximately 19 hours later. A normal horse should suppress cortisol following dexamethasone administration, and should have a post-dexamethasone cortisol concentration of < 27nmol/L (or <1 μg/dL or ~<30 pmol/L). Therefore a post-dexamethasone cortisol concentration greater than this is indicative of PPID.
Overnight dexamethasone suppression test (ODST) - Liphook Equine Hospital and Laboratory
Limitations of the DST:
There may be a risk of exacerbating laminitis. It will increase hyperinsulinaemia transiently.
Initial trials of the DST were diagnostic in horses that had advanced clinical disease - is there any evidence that the DST is sensitive for early PPID cases (see Beech et al. 2007 below)?
False positive results may be seen in the autumn and therefore the DST should be avoided during this time (July to October is suggested as months to avoid using the DST by Liphook).
The DST requires two vet visits and is therefore more expensive than the basal ACTH blood test.
According to Schott 2006 (below), no diagnostic or prognostic information is gleaned from the basal cortisol test - so why is this done?
Held F, Ekstrand C, Cvijovic M, Gabrielsson J, Jirstrand M
Modelling of oscillatory cortisol response in horses using a Bayesian population approach for evaluation of dexamethasone suppression test protocols
J Pharmacokinet Pharmacodyn. 2019 Feb;46(1):75-87. doi: 10.1007/s10928-018-09617-0. Epub 2019 Jan 23
J Am Vet Med Assoc. 2007 Aug 1;231(3):417-26. (PubMed)
Adrenocorticotropin concentration following administration of thyrotropin-releasing hormone in healthy horses and those with pituitary pars intermedia dysfunction and pituitary gland hyperplasia
Beech J, Boston R, Lindborg S, Russell GE
"Results of DST were abnormal only in clinically abnormal horses or those with pars intermedia hyperplasia, but were within reference range in 17 of 26 tests in these horses." "The DST was specific but not sensitive and was inconsistent for individuals, and results often did not agree with the TRH test response."
AAEP PROCEEDINGS 2006 Vol 52 (Full)
Pituitary Pars Intermedia Dysfunction: Challenges of Diagnosis and Treatment
Schott HC
See also Combined Dexamethasone Suppression/TRH stimulation test.
The dexamethasone suppression test (DST) was once considered the "gold standard" method of diagnosing PPID. However, this appears to have been based on research by Dybdal et al. published in 1994, which is now considered to have been "favourably biased" (see below). The resting ACTH blood test is now the test of choice for diagnosing PPID, has several advantages over the DST, and is the test recommended by The Laminitis Site.
The DST (sometimes called Overnight DST) involves collecting blood to test baseline cortisol in the late afternoon, then injecting 40μg/kg dexamethasone (20 mg/500 kg horse), then collecting a second blood sample to test cortisol the following morning, approximately 19 hours later. A normal horse should suppress cortisol following dexamethasone administration, and should have a post-dexamethasone cortisol concentration of < 27nmol/L (or <1 μg/dL or ~<30 pmol/L). Therefore a post-dexamethasone cortisol concentration greater than this is indicative of PPID.
Overnight dexamethasone suppression test (ODST) - Liphook Equine Hospital and Laboratory
Limitations of the DST:
There may be a risk of exacerbating laminitis. It will increase hyperinsulinaemia transiently.
Initial trials of the DST were diagnostic in horses that had advanced clinical disease - is there any evidence that the DST is sensitive for early PPID cases (see Beech et al. 2007 below)?
False positive results may be seen in the autumn and therefore the DST should be avoided during this time (July to October is suggested as months to avoid using the DST by Liphook).
The DST requires two vet visits and is therefore more expensive than the basal ACTH blood test.
According to Schott 2006 (below), no diagnostic or prognostic information is gleaned from the basal cortisol test - so why is this done?
Held F, Ekstrand C, Cvijovic M, Gabrielsson J, Jirstrand M
Modelling of oscillatory cortisol response in horses using a Bayesian population approach for evaluation of dexamethasone suppression test protocols
J Pharmacokinet Pharmacodyn. 2019 Feb;46(1):75-87. doi: 10.1007/s10928-018-09617-0. Epub 2019 Jan 23
J Am Vet Med Assoc. 2007 Aug 1;231(3):417-26. (PubMed)
Adrenocorticotropin concentration following administration of thyrotropin-releasing hormone in healthy horses and those with pituitary pars intermedia dysfunction and pituitary gland hyperplasia
Beech J, Boston R, Lindborg S, Russell GE
"Results of DST were abnormal only in clinically abnormal horses or those with pars intermedia hyperplasia, but were within reference range in 17 of 26 tests in these horses." "The DST was specific but not sensitive and was inconsistent for individuals, and results often did not agree with the TRH test response."
AAEP PROCEEDINGS 2006 Vol 52 (Full)
Pituitary Pars Intermedia Dysfunction: Challenges of Diagnosis and Treatment
Schott HC
|
Miesner TJ, Deard LA, Schmall SM, Reed SM (2003)
Results of overnight dexamethasone suppression test repeated over time in horses suspected of having equine Cushings disease. J Vet Intern Med 18, p 420. In 2003 Miesner et al. used the overnight dexamethasone suppression test three times 30 days apart on 7 horses showing clinical signs of PPID. Only 1 of the 7 horses tested positive for PPID in all three tests. 4 of the 7 horses did not test positive for PPID after the initial test, despite showing clinical signs of the disease. This suggested that the test was inaccurate in early cases of PPID (but they weren't that early - they had clinical signs!), and that the sensitivity of the test was lower than had originally been suggested. |
Courtesy of The Liphook Equine Hospital and Laboratory
|
J Am Vet Med Assoc. 1994 Feb 15;204(4):627-32. (PubMed)
Diagnostic testing for pituitary pars intermedia dysfunction in horses.
Dybdal NO, Hargreaves KM, Madigan JE, Gribble DH, Kennedy PC, Stabenfeldt GH.
"On the basis of plasma cortisol concentration, the dexamethasone suppression test, using 40 micrograms/kg, whether initiated at 5 PM with sample collection at 15 (8 AM) and 19 (12 PM) hours after dexamethasone administration, or initiated at 12 AM with sample collection at 8 (8 AM), 12 (12 PM), 16 (4 PM), 20 (8 PM), and 24 (12 AM) hours after dexamethasone administration, reliably distinguished between control horses and those with pituitary pars intermedia dysfunction."
According to the study, the ODST showed 100% sensitivity and specificity and was subsequently used as the "gold standard" test for diagnosing PPID. However, the horses were selected based on the presence of obvious clinical signs of PPID, including hirsutism, which is considered to be diagnostic for PPID, and is now thought to be a symptom of advanced PPID. It is possible that the loss of dexamethasone suppression happens late in the progression of PPID, and that the ODST is inaccurate for diagnosing early cases of PPID.
Clinical Forum: “Diagnosing Pituitary Pars Intermedia Dysfunction”, by Dianne MCFarlane; Equine Compendium, Vol 2, No. 4, July/August 2007
Diagnostic testing for pituitary pars intermedia dysfunction in horses.
Dybdal NO, Hargreaves KM, Madigan JE, Gribble DH, Kennedy PC, Stabenfeldt GH.
"On the basis of plasma cortisol concentration, the dexamethasone suppression test, using 40 micrograms/kg, whether initiated at 5 PM with sample collection at 15 (8 AM) and 19 (12 PM) hours after dexamethasone administration, or initiated at 12 AM with sample collection at 8 (8 AM), 12 (12 PM), 16 (4 PM), 20 (8 PM), and 24 (12 AM) hours after dexamethasone administration, reliably distinguished between control horses and those with pituitary pars intermedia dysfunction."
According to the study, the ODST showed 100% sensitivity and specificity and was subsequently used as the "gold standard" test for diagnosing PPID. However, the horses were selected based on the presence of obvious clinical signs of PPID, including hirsutism, which is considered to be diagnostic for PPID, and is now thought to be a symptom of advanced PPID. It is possible that the loss of dexamethasone suppression happens late in the progression of PPID, and that the ODST is inaccurate for diagnosing early cases of PPID.
Clinical Forum: “Diagnosing Pituitary Pars Intermedia Dysfunction”, by Dianne MCFarlane; Equine Compendium, Vol 2, No. 4, July/August 2007
The dexamethasone suppression test/treatment with dexamethasone has been shown to cause increases in insulin:
Journal of Equine Veterinary Science Volume 30, Issue 2, Page 103, February 2010
Seasonal Influence on Insulin and Cortisol Results from Overnight Dexamethasone Suppression Tests (DST) in Normal and Previously Laminitic Ponies
Borer KE, Menzies-Gow NJ, Berhane Y, Bailey SR, Harris PA, Elliott J
19 hour overnight DSTs were carried out in April, July and December on 6 normal and 6 previously laminitic ponies kept at grass.
Insulin results for previously laminitic ponies:
April basal 240 +/- 160 After DST 966 +/- 488
July basal 166 +/- 223 After DST 844 +/- 820
December basal 13 +/- 10 After DST 26 +/- 16
Insulin results for normal ponies:
April basal 98 +/- 94 After DST 246 +/- 146
July basal 22 +/- 20 After DST 206 +/- 204
December basal 10 +/- 5 After DST 28 +/- 16
Haffner JC, Eiler H, Hoffman RM, Fecteau KA, Oliver JW
Effect of a single dose of dexamethasone on glucose homeostasis in healthy horses by using the combined intravenous glucose and insulin test.
J Anim Sci. 2009 Jan;87(1):131-5. Epub 2008 Sep 26. (PubMed) Full paper
A single IV dose of 20 mg dexamethasone (the dose used for the DST) decreased the response to insulin at 2 and 24 hours.
.
JAVMA November 1, 2007, Vol. 231, No. 9, Pages 1365-1373
Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis
Bailey SR, Menzies-Gow NJ, Harris PA, Habershon-Butcher JL, Crawford C, Berhane Y, Boston RC, Elliott J
19 hour DSTs (0.04 mg/kg dexamethasone) were carried out in August on non-obese previously laminitic ponies (LP) and control ponies. The previously laminitic ponies had exagerated production of insulin in response to the DST.
Insulin results for previously laminitic ponies - median (interquartile range)
Basal insulin 38.7 mU/L (22.4 to 137.0 mU/L)
After DST 222.9 mU/L (102.1 to 367.7 mU/L)
The lowest serum insulin concentration after dexamethasone administration in LP ponies was 83.6 mU/L, and the highest was 488.3 mU/L.
Insulin results for control ponies - median (interquartile range)
Basal insulin 8.2 mU/L (5.6 to 16.9 mU/L)
After DST 45.6 mU/L (22.7 to 65.9 mU/L)
Timko KJ, Hostnik LD, Watts MR, Chen C, Bercz A, Toribio RE, Belknap JK, Burns TA.
Diagnostic evaluation of insulin and glucose dynamics in light-breed horses receiving dexamethasone.
Can Vet J. 2022 Jun;63(6):617-626. PMID: 35656529; PMCID: PMC9112365.
Oral dexamethasone induced insulin dysregulation; "horses treated with glucocorticoids should be considered at risk for development of insulin dysregulation".
Tiley HA, Geor RJ, McCutcheon LJ
Effects of dexamethasone administration on insulin resistance and components of insulin signaling and glucose metabolism in equine skeletal muscle
Am J Vet Res. 2008 Jan;69(1):51-8
Conclusion: "In horses, 21 days of dexamethasone treatment resulted in substantial insulin resistance".
Am J Vet Res. 2007 Jul;68(7):753-9. (PubMed)
Effects of dexamethasone on glucose dynamics and insulin sensitivity in healthy horses
Tiley HA, Geor RJ, McCutcheon LJ
In a balanced crossover study, 6 adult standardbred horses received dexamethasone (0.08 mg/ kg, IV, q 48 h) or an equivalent volume of saline (0.9% NaCl) solution (control treatment) during a 21-day period.
"RESULTS: Mean serum insulin concentration was significantly higher in dexamethasone-treated horses than control horses on days 7, 14, and 21. Similarly, mean plasma glucose concentration was higher in dexamethasone-treated horses on days 7, 14, and 21; this value differed significantly on day 14 but not on days 7 or 21. Minimal model analysis of FSIGT data revealed a significant decrease in Si and a significant increase in AIRg after dexamethasone treatment, with no change in Sg or disposition index. Mean RISQI was significantly lower, whereas MIRG was higher, in dexamethasone-treated horses than control horses on days 7, 14, and 21.
CONCLUSIONS AND CLINICAL RELEVANCE: The study revealed marked insulin resistance in healthy horses after 21 days of dexamethasone administration. Because insulin resistance has been associated with a predisposition to laminitis, a glucocorticoid-induced decrease in insulin sensitivity may increase risk for development of laminitis in some horses and ponies."
Journal of Equine Veterinary Science Volume 30, Issue 2, Page 103, February 2010
Seasonal Influence on Insulin and Cortisol Results from Overnight Dexamethasone Suppression Tests (DST) in Normal and Previously Laminitic Ponies
Borer KE, Menzies-Gow NJ, Berhane Y, Bailey SR, Harris PA, Elliott J
19 hour overnight DSTs were carried out in April, July and December on 6 normal and 6 previously laminitic ponies kept at grass.
Insulin results for previously laminitic ponies:
April basal 240 +/- 160 After DST 966 +/- 488
July basal 166 +/- 223 After DST 844 +/- 820
December basal 13 +/- 10 After DST 26 +/- 16
Insulin results for normal ponies:
April basal 98 +/- 94 After DST 246 +/- 146
July basal 22 +/- 20 After DST 206 +/- 204
December basal 10 +/- 5 After DST 28 +/- 16
Haffner JC, Eiler H, Hoffman RM, Fecteau KA, Oliver JW
Effect of a single dose of dexamethasone on glucose homeostasis in healthy horses by using the combined intravenous glucose and insulin test.
J Anim Sci. 2009 Jan;87(1):131-5. Epub 2008 Sep 26. (PubMed) Full paper
A single IV dose of 20 mg dexamethasone (the dose used for the DST) decreased the response to insulin at 2 and 24 hours.
.
JAVMA November 1, 2007, Vol. 231, No. 9, Pages 1365-1373
Effect of dietary fructans and dexamethasone administration on the insulin response of ponies predisposed to laminitis
Bailey SR, Menzies-Gow NJ, Harris PA, Habershon-Butcher JL, Crawford C, Berhane Y, Boston RC, Elliott J
19 hour DSTs (0.04 mg/kg dexamethasone) were carried out in August on non-obese previously laminitic ponies (LP) and control ponies. The previously laminitic ponies had exagerated production of insulin in response to the DST.
Insulin results for previously laminitic ponies - median (interquartile range)
Basal insulin 38.7 mU/L (22.4 to 137.0 mU/L)
After DST 222.9 mU/L (102.1 to 367.7 mU/L)
The lowest serum insulin concentration after dexamethasone administration in LP ponies was 83.6 mU/L, and the highest was 488.3 mU/L.
Insulin results for control ponies - median (interquartile range)
Basal insulin 8.2 mU/L (5.6 to 16.9 mU/L)
After DST 45.6 mU/L (22.7 to 65.9 mU/L)
Timko KJ, Hostnik LD, Watts MR, Chen C, Bercz A, Toribio RE, Belknap JK, Burns TA.
Diagnostic evaluation of insulin and glucose dynamics in light-breed horses receiving dexamethasone.
Can Vet J. 2022 Jun;63(6):617-626. PMID: 35656529; PMCID: PMC9112365.
Oral dexamethasone induced insulin dysregulation; "horses treated with glucocorticoids should be considered at risk for development of insulin dysregulation".
Tiley HA, Geor RJ, McCutcheon LJ
Effects of dexamethasone administration on insulin resistance and components of insulin signaling and glucose metabolism in equine skeletal muscle
Am J Vet Res. 2008 Jan;69(1):51-8
Conclusion: "In horses, 21 days of dexamethasone treatment resulted in substantial insulin resistance".
Am J Vet Res. 2007 Jul;68(7):753-9. (PubMed)
Effects of dexamethasone on glucose dynamics and insulin sensitivity in healthy horses
Tiley HA, Geor RJ, McCutcheon LJ
In a balanced crossover study, 6 adult standardbred horses received dexamethasone (0.08 mg/ kg, IV, q 48 h) or an equivalent volume of saline (0.9% NaCl) solution (control treatment) during a 21-day period.
"RESULTS: Mean serum insulin concentration was significantly higher in dexamethasone-treated horses than control horses on days 7, 14, and 21. Similarly, mean plasma glucose concentration was higher in dexamethasone-treated horses on days 7, 14, and 21; this value differed significantly on day 14 but not on days 7 or 21. Minimal model analysis of FSIGT data revealed a significant decrease in Si and a significant increase in AIRg after dexamethasone treatment, with no change in Sg or disposition index. Mean RISQI was significantly lower, whereas MIRG was higher, in dexamethasone-treated horses than control horses on days 7, 14, and 21.
CONCLUSIONS AND CLINICAL RELEVANCE: The study revealed marked insulin resistance in healthy horses after 21 days of dexamethasone administration. Because insulin resistance has been associated with a predisposition to laminitis, a glucocorticoid-induced decrease in insulin sensitivity may increase risk for development of laminitis in some horses and ponies."
Diabetes
Need to know:
When a horse has diabetes mellitus (DM), blood glucose levels are significantly higher than normal - this is called hyperglycaemia.
DM happens when the horse doesn't make enough insulin, or the insulin doesn't work properly (insulin resistance).
DM appears to be very rare in horses. In most horses with insulin resistance, increased amounts of insulin produced "compensate" for the insulin resistance and prevent blood glucose levels becoming abnormally high - unlike in humans, insulin resistance in horses doesn't usually develop into diabetes mellitus.
Horses with insulin resistance have above normal insulin but normal glucose.
Horses with DM have above normal glucose but normal/low insulin.
High levels of glucose in the blood (>180/200 mg/dl) can lead to glucosuria - glucose in the urine.
DM and hyperglycaemia are most commonly seen in horses with PPID.
Diabetes mellitus is associated with persistent hyperglycaemia (above normal blood glucose levels) due to reduced production or reduced sensitivity to insulin.
Type 1 or insulin-dependent diabetes mellitus occurs as a result of a primary insulin deficiency due to destruction of pancreatic beta cells (e.g. due to pancreatitis) and is reported infrequently in horses.
Type 2 or non-insulin-dependent diabetes mellitus is the more common form and mostly reported in older horses with PPID. Diagnosis of T2DM is based on low insulin sensitivity/marked insulin resistance and low to no discernible insulin response (by pancreatic beta-cells) to glucose.
Treiber et al. 2005 suggested that type 2 diabetes mellitus rarely occurs in horses; Durham et al. 2009 suggested that type 2 diabetes mellitus may be more common in horses than generally considered.
(Theoretical reasons for T2DM to develop: chronic insulin resistance progresses into pancreatic exhaustion (as with humans.
Hyperglycaemia may develop in horses with PPID due to high levels of cortisol - although above normal levels of cortisol are not commonly seen in horses with PPID. Therefore should PPID horses with hyperglycaemia have cortisol tested?).
The clinical symptoms of diabetes are weight loss and PU/PD. Sometimes excessive appetite, depression and exercise intolerance are seen.
Diagnosis of DM uses similar tests to insulin resistance: fasting resting insulin and glucose, euglycaemic hyperinsulinaemic clamp technique, frequently sampled intravenous glucose tolerance test, minimal model analysis of insulin-glucose dynamics.
The Lloyd Guide to Insulin Resistance and Laminitis p 31 suggests that testing should be carried out for DM if resting fasting glucose > 120 mg/dl with insulin < 20 µIU/ml.
High levels of blood glucose (greater than 11 mmol/l or 200 mg/dl) lead to glucosuria - glucose in the urine. Normal horse urine does not contain glucose. See Equine Clinical Medicine, Surgery and Reproduction - Graham Munroe, Scott Weese
Treatment of DM will depend on identifying an underlying cause - if one is found, that should be treated (e.g. PPID is treated with pergolide/Prascend). Otherwise there is currently no recommended standard treatment of diabetes in horses, and treatment should consist of medication, diet and exercise. Durham et al. treated 2 horses with T2DM with metformin (15 mg/kg PO every 12 hours). One horse developed clinical signs of hypoglycaemia after 10 days of treatment. Treatment was withdrawn, hyperglycaemia recurred, so treatment with metformin was re-introduced at 7.5 - 9.5 mg/kg PO every 12 hours and euglycaemia was reached. The other horse did not respond to metformin treatment after 22 days and oral glibenclamide (glyburide) treatment (0.3 mg/kg PO every 12 hours) was started.
Expert advice should be sought.
According to Phillip Johnson, the optimal diet for management of DM in horses is unknown, but a diet based on high fibre, low NSC and oil for added calories if necessary seems logical.
Johnson PJ, Wiedmeyer CE, LaCarrubba A, Ganjam VK, Messer NT
Diabetes, Insulin Resistance, and Metabolic Syndrome in Horses
Journal of Diabetes Science and Technology Volume 6, Issue 3, May 2012
"horses may develop type 2 DM as a result of IR and EMS, but DM is relatively uncommonly identified in the equine species".
Nutritional and Therapeutic Interventions for Diabetes and Metabolic Syndrome - Edited by Debasis Bagchi, Nair Sreejayan 2012
p 507 Diabetes in Horses
Durham AE, Hughes KJ, Cottle HJ, Rendle DI, Boston RC
Type 2 diabetes mellitus with pancreatic beta cell dysfunction in 3 horses confirmed with minimal model analysis
Equine Vet J. 2009 Dec;41(9):924-9 (PubMed)
"OBJECTIVES: Three cases of diabetes mellitus were investigated using a specific test for insulin sensitivity and pancreatic beta cell function in order to define accurately and characterise the existence of T2DM in all 3 subjects.
METHODS: The insulin-modified frequently sampled i.v. glucose tolerance test was performed in each case and the data so obtained were subject to minimal model analysis of insulin-glucose dynamics. Cases were then monitored following treatment using a combination of dietary modification, metformin, glibenclamide and pergolide.
RESULTS: Marked insulin resistance was identified in each case and, furthermore, severe pancreatic beta cell dysfunction was present therefore classifying each case as end stage T2DM. Treatment was nevertheless associated with restoration of normoglycaemia in all cases.
CONCLUSIONS: T2DM in horses may be more common than generally considered.In some cases individuals may respond to therapy aimed at restoring insulin sensitivity and pancreatic function. Drugs used in other species for the treatment of T2DM have not yet been adequately tested in horses.
POTENTIAL RELEVANCE: T2DM should be considered as an important differential diagnosis in mature to elderly horses and ponies suffering from weight loss, polydipsia and polyuria. Clinicians should be encouraged to offer treatment and management advice when such cases are encountered."
Comment on above research in theHorse.com - Older Horses Doing Poorly Could Have Diabetes - Stacey Oke April 19 2010, Article # 16202
Blackwell's Five-Minute Veterinary Consult: Equine 2009 - Glucose p 346
McFarlane D
Equine pituitary pars intermedia dysfunction
Vet Clin North Am Equine Pract. 2011 Apr;27(1):93-113 (PubMed)
The most common biochemistry abnormality in a horse with PPID is hyperglycemia.
"Although non-specific, when hyperglycemia is present in routine blood analysis of an aged horse, PPID should be considered."
Baker JR, Ritchie HE
Diabetes Mellitus in the Horse: a Case Report and Review of the Literature
Equine Veterinary Journal Volume 6, Issue 1, pages 7–11, January 1974
A mare with diabetes mellitus showed rapid weight loss, abnormal glucose tolerance and no response to insulin. Post mortem findings included a tumour in the pars intermedia, adrenal cortical hyperplasia and depletion of the beta cells of the pancreatic islets.
Jill K. Giri, K. Gary Magdesian, and Patricia M. Gaffney
Insulin-dependent diabetes mellitus associated with presumed autoimmune polyendocrine syndrome in a mare
Can Vet J. 2011 May; 52(5): 506–512 (Full)
Johnson PJ, Scotty NC, Wiedmeyer C, Messer NT, Kreeger JM.
Diabetes mellitus in a domesticated Spanish mustang.
J Am Vet Med Assoc. 2005 Feb 15;226(4):584-8, 542. doi: 10.2460/javma.2005.226.584. PMID: 15742701.
An 18 year old Spanish Mustang mare had progressive weight loss, hyperglycemia and glycosuria. PPID was ruled out with a dexamethasone suppression test. Serum insulin and plasma C-peptide concentrations were low, suggesting that the high blood glucose was due to reduced insulin secretion from the pancreas. Giving IV insulin only slightly decreased blood glucose levels, suggesting that the action of insulin was impaired. Within 5 hours of giving a combination of glyburide and metformin, blood glucose levels returned to normal. The horse was euthanized [so information about long-term use of these drugs is not available from this research]. Post mortem examination showed reduced beta-cells in the pancreas. Pancreatic beta-cell failure is rare, but may contribute to the development of diabetes mellitus in horses.
When a horse has diabetes mellitus (DM), blood glucose levels are significantly higher than normal - this is called hyperglycaemia.
DM happens when the horse doesn't make enough insulin, or the insulin doesn't work properly (insulin resistance).
DM appears to be very rare in horses. In most horses with insulin resistance, increased amounts of insulin produced "compensate" for the insulin resistance and prevent blood glucose levels becoming abnormally high - unlike in humans, insulin resistance in horses doesn't usually develop into diabetes mellitus.
Horses with insulin resistance have above normal insulin but normal glucose.
Horses with DM have above normal glucose but normal/low insulin.
High levels of glucose in the blood (>180/200 mg/dl) can lead to glucosuria - glucose in the urine.
DM and hyperglycaemia are most commonly seen in horses with PPID.
Diabetes mellitus is associated with persistent hyperglycaemia (above normal blood glucose levels) due to reduced production or reduced sensitivity to insulin.
Type 1 or insulin-dependent diabetes mellitus occurs as a result of a primary insulin deficiency due to destruction of pancreatic beta cells (e.g. due to pancreatitis) and is reported infrequently in horses.
Type 2 or non-insulin-dependent diabetes mellitus is the more common form and mostly reported in older horses with PPID. Diagnosis of T2DM is based on low insulin sensitivity/marked insulin resistance and low to no discernible insulin response (by pancreatic beta-cells) to glucose.
Treiber et al. 2005 suggested that type 2 diabetes mellitus rarely occurs in horses; Durham et al. 2009 suggested that type 2 diabetes mellitus may be more common in horses than generally considered.
(Theoretical reasons for T2DM to develop: chronic insulin resistance progresses into pancreatic exhaustion (as with humans.
Hyperglycaemia may develop in horses with PPID due to high levels of cortisol - although above normal levels of cortisol are not commonly seen in horses with PPID. Therefore should PPID horses with hyperglycaemia have cortisol tested?).
The clinical symptoms of diabetes are weight loss and PU/PD. Sometimes excessive appetite, depression and exercise intolerance are seen.
Diagnosis of DM uses similar tests to insulin resistance: fasting resting insulin and glucose, euglycaemic hyperinsulinaemic clamp technique, frequently sampled intravenous glucose tolerance test, minimal model analysis of insulin-glucose dynamics.
The Lloyd Guide to Insulin Resistance and Laminitis p 31 suggests that testing should be carried out for DM if resting fasting glucose > 120 mg/dl with insulin < 20 µIU/ml.
High levels of blood glucose (greater than 11 mmol/l or 200 mg/dl) lead to glucosuria - glucose in the urine. Normal horse urine does not contain glucose. See Equine Clinical Medicine, Surgery and Reproduction - Graham Munroe, Scott Weese
Treatment of DM will depend on identifying an underlying cause - if one is found, that should be treated (e.g. PPID is treated with pergolide/Prascend). Otherwise there is currently no recommended standard treatment of diabetes in horses, and treatment should consist of medication, diet and exercise. Durham et al. treated 2 horses with T2DM with metformin (15 mg/kg PO every 12 hours). One horse developed clinical signs of hypoglycaemia after 10 days of treatment. Treatment was withdrawn, hyperglycaemia recurred, so treatment with metformin was re-introduced at 7.5 - 9.5 mg/kg PO every 12 hours and euglycaemia was reached. The other horse did not respond to metformin treatment after 22 days and oral glibenclamide (glyburide) treatment (0.3 mg/kg PO every 12 hours) was started.
Expert advice should be sought.
According to Phillip Johnson, the optimal diet for management of DM in horses is unknown, but a diet based on high fibre, low NSC and oil for added calories if necessary seems logical.
Johnson PJ, Wiedmeyer CE, LaCarrubba A, Ganjam VK, Messer NT
Diabetes, Insulin Resistance, and Metabolic Syndrome in Horses
Journal of Diabetes Science and Technology Volume 6, Issue 3, May 2012
"horses may develop type 2 DM as a result of IR and EMS, but DM is relatively uncommonly identified in the equine species".
Nutritional and Therapeutic Interventions for Diabetes and Metabolic Syndrome - Edited by Debasis Bagchi, Nair Sreejayan 2012
p 507 Diabetes in Horses
Durham AE, Hughes KJ, Cottle HJ, Rendle DI, Boston RC
Type 2 diabetes mellitus with pancreatic beta cell dysfunction in 3 horses confirmed with minimal model analysis
Equine Vet J. 2009 Dec;41(9):924-9 (PubMed)
"OBJECTIVES: Three cases of diabetes mellitus were investigated using a specific test for insulin sensitivity and pancreatic beta cell function in order to define accurately and characterise the existence of T2DM in all 3 subjects.
METHODS: The insulin-modified frequently sampled i.v. glucose tolerance test was performed in each case and the data so obtained were subject to minimal model analysis of insulin-glucose dynamics. Cases were then monitored following treatment using a combination of dietary modification, metformin, glibenclamide and pergolide.
RESULTS: Marked insulin resistance was identified in each case and, furthermore, severe pancreatic beta cell dysfunction was present therefore classifying each case as end stage T2DM. Treatment was nevertheless associated with restoration of normoglycaemia in all cases.
CONCLUSIONS: T2DM in horses may be more common than generally considered.In some cases individuals may respond to therapy aimed at restoring insulin sensitivity and pancreatic function. Drugs used in other species for the treatment of T2DM have not yet been adequately tested in horses.
POTENTIAL RELEVANCE: T2DM should be considered as an important differential diagnosis in mature to elderly horses and ponies suffering from weight loss, polydipsia and polyuria. Clinicians should be encouraged to offer treatment and management advice when such cases are encountered."
Comment on above research in theHorse.com - Older Horses Doing Poorly Could Have Diabetes - Stacey Oke April 19 2010, Article # 16202
Blackwell's Five-Minute Veterinary Consult: Equine 2009 - Glucose p 346
McFarlane D
Equine pituitary pars intermedia dysfunction
Vet Clin North Am Equine Pract. 2011 Apr;27(1):93-113 (PubMed)
The most common biochemistry abnormality in a horse with PPID is hyperglycemia.
"Although non-specific, when hyperglycemia is present in routine blood analysis of an aged horse, PPID should be considered."
Baker JR, Ritchie HE
Diabetes Mellitus in the Horse: a Case Report and Review of the Literature
Equine Veterinary Journal Volume 6, Issue 1, pages 7–11, January 1974
A mare with diabetes mellitus showed rapid weight loss, abnormal glucose tolerance and no response to insulin. Post mortem findings included a tumour in the pars intermedia, adrenal cortical hyperplasia and depletion of the beta cells of the pancreatic islets.
Jill K. Giri, K. Gary Magdesian, and Patricia M. Gaffney
Insulin-dependent diabetes mellitus associated with presumed autoimmune polyendocrine syndrome in a mare
Can Vet J. 2011 May; 52(5): 506–512 (Full)
Johnson PJ, Scotty NC, Wiedmeyer C, Messer NT, Kreeger JM.
Diabetes mellitus in a domesticated Spanish mustang.
J Am Vet Med Assoc. 2005 Feb 15;226(4):584-8, 542. doi: 10.2460/javma.2005.226.584. PMID: 15742701.
An 18 year old Spanish Mustang mare had progressive weight loss, hyperglycemia and glycosuria. PPID was ruled out with a dexamethasone suppression test. Serum insulin and plasma C-peptide concentrations were low, suggesting that the high blood glucose was due to reduced insulin secretion from the pancreas. Giving IV insulin only slightly decreased blood glucose levels, suggesting that the action of insulin was impaired. Within 5 hours of giving a combination of glyburide and metformin, blood glucose levels returned to normal. The horse was euthanized [so information about long-term use of these drugs is not available from this research]. Post mortem examination showed reduced beta-cells in the pancreas. Pancreatic beta-cell failure is rare, but may contribute to the development of diabetes mellitus in horses.
Diet
See Feeding horses with laminitis/EMS/PPID
The diet for a laminitic horse will depend on several factors including the cause of the laminitis, the severity of the laminitis (symptoms and blood results) and whether acute or chronic, whether the horse needs to lose or gain weight and its management, but in general a diet based on grass hay with adequate protein, minerals and vitamins, and perhaps omega 3, will be suitable. NEVER STARVE A HORSE, PONY OR DONKEY WITH LAMINITIS - this can cause hyperlipaemia which can be fatal (particularly in donkeys, ponies and miniature horse breeds) - unless directed otherwise by your vet , feed at least 1.5% of the horse's bodyweight (in dry matter), so a 500 kg horse will need 7.5 kg of dry food - which would be 8.25 kg of a hay that was 10% water. Most laminitis (around 90% of all cases) is endocrinopathic, due to insulin dysregulation (ID). Horses with ID / endocrinopathic laminitis (due to EMS or PPID) need to have the total amount of sugar and starch in the diet kept low, ideally ESC (or simple sugars) plus starch should not exceed 10%. If you don't know the cause of the laminitis, assume endocrinopathic / ID until you know otherwise, and feed accordingly keeping sugar and starch low.
Emergency diet
Hay - feed approx. 1.5-2% bodyweight hay (depending on whether weight loss is needed (1.5%) or not (2%), so 7.5-10 kg for a 500 kg horse, 3.75-5 kg for a 250 kg pony), soaked for at least 1 hour then drained to reduce sugars. If hay is analysed by wet chemistry for ethanol soluble sugars (ESC) and starch (we recommend Equi-Analytical in the USA), and has an ESC plus starch content of <10%, it may not need to be soaked, although minimizing sugar in the diet may be ideal particularly when insulin levels are high/a horse is in pain from laminitis.
Forage balancer or mineral/vitamin supplement containing good levels of zinc (400 mg), copper (100 mg) and selenium (1 mg) (figures in brackets are the NRC Nutrient Requirements of Horses 2007 minimum RDAs for an average 500 kg horse not in work), and protein if hay does not provide sufficient protein. We recommend Spillers Lite + Lean.
Salt - total daily salt requirements are 25 g 500 kg horse not in work, 12.5 g 250 kg pony (a tablespoon of salt weighs around 21 g) - check salt/sodium amount in the rest of the diet and add more if necessary, plain table salt can be used.
Optionally, a low sugar chaff to mix with minerals, e.g. Dengie HiFi Molasses Free (weight loss/maintenance) or rinsed unmolassed sugar beet (weight gain/maintenance).
Vitamin E - approx. 300-400 IU/100 kg bodyweight (so 1500-2000 IU for a 500 kg horse, 750-1000 for a 250 kg pony) - check amount in mineral supplement/balancer and add more if necessary, human vitamin E capsules can be added to the feed.
Micronised linseed may be fed to provide essential fatty acids and omega 3, at the rate of 50 - 100 g, or this may be added to the diet later. Suppliers in the UK include Charnwood Milling and EquiSupermarket.
Do not feed:
Grass
Cereals (oats, barley, maize) or bagged feeds containing cereals or molasses with combined sugar/starch exceeding 10%.
Treats containing sugar/starch
Putting the diet together
You don't count water content when calculating how much a horse needs to eat - diet is calculated on a Dry Matter (DM) basis.
Hay is often around 10% water, so if your horse weighs 500 kg and doesn't need to lose weight, and you want to feed 2% of his bodyweight, that would be 500 kg x 2% = 10 kg hay DM, which would be 10 kg / 90% (dry matter) = 11.1 kg hay as fed. Remember to weigh hay before soaking it.
Haylage may be suitable to feed to horses with laminitis, especially high fibre or Timothy varieties that come with an analysis - combined sugar and starch is often less than 10% on a dry matter basis. Haylage has a higher water content than water and is often around 55 - 60% DM (so 45 - 40% water). To feed 10 kg DM of 60% DM haylage, you would feed 10 kg/60% = 16.67 kg as fed. Soaking haylage is not recommended because there is a risk of secondary fermentation, and soaking to further reduce sugar content shouldn't be necessary with correctly made haylage.
TLS forum: Recommended Diet
Managing Laminitis-prone Horses - Pat Harris - www.thehorse.com June 2011
Tips for feeding, access to pasture and exercise for the laminitis-prone horse. NB note it has since been shown that fructans (the difference between WSC and ESC) do not increase insulin and therefore are unlikely to be a factor in endocrinopathic / pasture associated laminitis - replace "NSC" by ESC + starch, and replace "WSC" by ESC.
The diet for a laminitic horse will depend on several factors including the cause of the laminitis, the severity of the laminitis (symptoms and blood results) and whether acute or chronic, whether the horse needs to lose or gain weight and its management, but in general a diet based on grass hay with adequate protein, minerals and vitamins, and perhaps omega 3, will be suitable. NEVER STARVE A HORSE, PONY OR DONKEY WITH LAMINITIS - this can cause hyperlipaemia which can be fatal (particularly in donkeys, ponies and miniature horse breeds) - unless directed otherwise by your vet , feed at least 1.5% of the horse's bodyweight (in dry matter), so a 500 kg horse will need 7.5 kg of dry food - which would be 8.25 kg of a hay that was 10% water. Most laminitis (around 90% of all cases) is endocrinopathic, due to insulin dysregulation (ID). Horses with ID / endocrinopathic laminitis (due to EMS or PPID) need to have the total amount of sugar and starch in the diet kept low, ideally ESC (or simple sugars) plus starch should not exceed 10%. If you don't know the cause of the laminitis, assume endocrinopathic / ID until you know otherwise, and feed accordingly keeping sugar and starch low.
Emergency diet
Hay - feed approx. 1.5-2% bodyweight hay (depending on whether weight loss is needed (1.5%) or not (2%), so 7.5-10 kg for a 500 kg horse, 3.75-5 kg for a 250 kg pony), soaked for at least 1 hour then drained to reduce sugars. If hay is analysed by wet chemistry for ethanol soluble sugars (ESC) and starch (we recommend Equi-Analytical in the USA), and has an ESC plus starch content of <10%, it may not need to be soaked, although minimizing sugar in the diet may be ideal particularly when insulin levels are high/a horse is in pain from laminitis.
Forage balancer or mineral/vitamin supplement containing good levels of zinc (400 mg), copper (100 mg) and selenium (1 mg) (figures in brackets are the NRC Nutrient Requirements of Horses 2007 minimum RDAs for an average 500 kg horse not in work), and protein if hay does not provide sufficient protein. We recommend Spillers Lite + Lean.
Salt - total daily salt requirements are 25 g 500 kg horse not in work, 12.5 g 250 kg pony (a tablespoon of salt weighs around 21 g) - check salt/sodium amount in the rest of the diet and add more if necessary, plain table salt can be used.
Optionally, a low sugar chaff to mix with minerals, e.g. Dengie HiFi Molasses Free (weight loss/maintenance) or rinsed unmolassed sugar beet (weight gain/maintenance).
Vitamin E - approx. 300-400 IU/100 kg bodyweight (so 1500-2000 IU for a 500 kg horse, 750-1000 for a 250 kg pony) - check amount in mineral supplement/balancer and add more if necessary, human vitamin E capsules can be added to the feed.
Micronised linseed may be fed to provide essential fatty acids and omega 3, at the rate of 50 - 100 g, or this may be added to the diet later. Suppliers in the UK include Charnwood Milling and EquiSupermarket.
Do not feed:
Grass
Cereals (oats, barley, maize) or bagged feeds containing cereals or molasses with combined sugar/starch exceeding 10%.
Treats containing sugar/starch
Putting the diet together
You don't count water content when calculating how much a horse needs to eat - diet is calculated on a Dry Matter (DM) basis.
Hay is often around 10% water, so if your horse weighs 500 kg and doesn't need to lose weight, and you want to feed 2% of his bodyweight, that would be 500 kg x 2% = 10 kg hay DM, which would be 10 kg / 90% (dry matter) = 11.1 kg hay as fed. Remember to weigh hay before soaking it.
Haylage may be suitable to feed to horses with laminitis, especially high fibre or Timothy varieties that come with an analysis - combined sugar and starch is often less than 10% on a dry matter basis. Haylage has a higher water content than water and is often around 55 - 60% DM (so 45 - 40% water). To feed 10 kg DM of 60% DM haylage, you would feed 10 kg/60% = 16.67 kg as fed. Soaking haylage is not recommended because there is a risk of secondary fermentation, and soaking to further reduce sugar content shouldn't be necessary with correctly made haylage.
TLS forum: Recommended Diet
Managing Laminitis-prone Horses - Pat Harris - www.thehorse.com June 2011
Tips for feeding, access to pasture and exercise for the laminitis-prone horse. NB note it has since been shown that fructans (the difference between WSC and ESC) do not increase insulin and therefore are unlikely to be a factor in endocrinopathic / pasture associated laminitis - replace "NSC" by ESC + starch, and replace "WSC" by ESC.
Digital pulse
Horses with laminitis will often have a "bounding" digital pulse (the pulse in the digital artery in the lower leg). Checking the digital pulse can be one of the best ways to detect if a horse has or is developing laminitis, or has chronic laminitis (uncorrected rotation), or another problem in the foot e.g. an abscess or bruising. It's also an easy place to measure a horse's heart rate.
The digital pulse is measured with your finger/s, on both the outside and inside of each leg, on the fetlock or on the pastern.
Learn to check the digital pulse before you need to - it's much easier to learn when you aren't worrying that your horse is ill. Ideally ask someone who is confident checking the pulse to show you exactly where to put your finger - put your finger above or below theirs on the artery and count the pulse together to be certain you are feeling the right thing.
The digital pulse is measured with your finger/s, on both the outside and inside of each leg, on the fetlock or on the pastern.
Learn to check the digital pulse before you need to - it's much easier to learn when you aren't worrying that your horse is ill. Ideally ask someone who is confident checking the pulse to show you exactly where to put your finger - put your finger above or below theirs on the artery and count the pulse together to be certain you are feeling the right thing.
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Watch these videos, or look at the diagrams in the links below, to see where you should feel for the pulse, then lightly move your finger around this area until you feel something like a fairly firm strand of spaghetti. Put your finger over this "strand of spaghetti" and, if necessary, vary your finger pressure until you can feel a pulse. If it helps, ask someone to mark the artery for you so you can practise with confidence.
To check the heart rate, count the pulse for 15 seconds then multiply by 4 (or for slightly more accuracy count for 30 seconds then multiply by 2). You might double-check the digital pulse against the mandibular artery pulse (near the lower jaw bone) until you are confident.
When looking for signs of laminitis or other foot problems, it is the "boundingness" or strength of the pulse that you are assessing - a really bounding pulse can move your finger. To be able to assess this, you have to know what is normal, and how your horse's digital pulse varies - normally - through the day. In a healthy foot on a calm horse standing on soft ground, the digital pulse can be hard to find, but exercise, heat, excitement and hard surfaces can make the digital pulse more bounding and easy to find. (Note that a horse with laminitis or suspected laminitis should never stand on a hard surface - feet should be well cushioned and supported with pads and/or conforming bedding/ground at all times).
To help assess whether a more bounding digital pulse indicates a foot problem or something affecting the whole body, check the mandibular artery pulse too - if only the digital pulse is bounding, this may be more suggestive of a foot problem.
Practise taking the digital pulse at every opportunity, and on lots of different horses (as long as you can do so safely!). It's a skill a bit like riding a bike - it can take a few tries to get it right, but once you've got it you'll always be able to find the pulse, and you could make a real difference to a horse by identifying a potentially serious problem early.
Equine Digital Pulses - www.ironfreehoof.com
Equine Digital Pulses - Anatomy of the Equine (great diagrams but note most laminitis does not involve significant inflammation in the feet)
Digital pulse - Easycare Inc
How to take your horse's digital pulse - Horses and People Magazine
When looking for signs of laminitis or other foot problems, it is the "boundingness" or strength of the pulse that you are assessing - a really bounding pulse can move your finger. To be able to assess this, you have to know what is normal, and how your horse's digital pulse varies - normally - through the day. In a healthy foot on a calm horse standing on soft ground, the digital pulse can be hard to find, but exercise, heat, excitement and hard surfaces can make the digital pulse more bounding and easy to find. (Note that a horse with laminitis or suspected laminitis should never stand on a hard surface - feet should be well cushioned and supported with pads and/or conforming bedding/ground at all times).
To help assess whether a more bounding digital pulse indicates a foot problem or something affecting the whole body, check the mandibular artery pulse too - if only the digital pulse is bounding, this may be more suggestive of a foot problem.
Practise taking the digital pulse at every opportunity, and on lots of different horses (as long as you can do so safely!). It's a skill a bit like riding a bike - it can take a few tries to get it right, but once you've got it you'll always be able to find the pulse, and you could make a real difference to a horse by identifying a potentially serious problem early.
Equine Digital Pulses - www.ironfreehoof.com
Equine Digital Pulses - Anatomy of the Equine (great diagrams but note most laminitis does not involve significant inflammation in the feet)
Digital pulse - Easycare Inc
How to take your horse's digital pulse - Horses and People Magazine
Distal descent (sinking)
Acute sinking
According to Pete Ramey (Care and Rehabilitation of the Equine Foot p 358), "sudden and dramatic" distal descent of P3 is rare but can occur when acute laminitis completely destroys the laminar attachments and the hoof is peripherally loaded (by shoes/long walls). The risk of distal descent can be lessened by reducing the weightbearing role of the walls at the first sign of laminitis, by trimming and bevelling the walls and/or using thick padding.
When such distal descent does occur, the walls should be completely removed from weightbearing and thick foam padding and boots used to support and protect the sole, frog and bars.
Reversing distal descent of P3 - Pete Ramey - 2005
After the Crash - Lessons from Chronic Laminitis - Chris Pollitt
Physiological trimming for a healthy equine foot - Robert Bowker - Michigan State University
Acute sinking
According to Pete Ramey (Care and Rehabilitation of the Equine Foot p 358), "sudden and dramatic" distal descent of P3 is rare but can occur when acute laminitis completely destroys the laminar attachments and the hoof is peripherally loaded (by shoes/long walls). The risk of distal descent can be lessened by reducing the weightbearing role of the walls at the first sign of laminitis, by trimming and bevelling the walls and/or using thick padding.
When such distal descent does occur, the walls should be completely removed from weightbearing and thick foam padding and boots used to support and protect the sole, frog and bars.
Reversing distal descent of P3 - Pete Ramey - 2005
After the Crash - Lessons from Chronic Laminitis - Chris Pollitt
Physiological trimming for a healthy equine foot - Robert Bowker - Michigan State University
Domperidone
Domperidone, a synthetic benzimidazole, is a dopamine receptor antagonist which blocks peripheral dopamine D2 receptors, thereby increasing the release of POMC-derived peptides, including ACTH, alpha-MSH, beta-endorphin and CLIP. Domperidone is approved for treating endophyte-associated agalactia in mares.
Domperidone - Patrick McCue Colorado State University
It had been thought that a domperidone stimulation test might be a good diagnostic test for PPID. However Jill Beech compared ACTH measurements in 28 horses after domperidone administration and after TRH administration, and found that TRH stimulation gave more consistent results:
J Am Vet Med Assoc. 2011 May 15;238(10):1305-15.
α-Melanocyte--stimulating hormone and adrenocorticotropin concentrations in response to thyrotropin-releasing hormone and comparison with adrenocorticotropin concentration after domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction
Beech J, McFarlane D, Lindborg S, Sojka JE, Boston RC
"The change in ACTH concentration after domperidone administration was less consistent in differentiating clinically normal horses from those with PPID than was the response to TRH."
Miller MA, Pardo ID, Jackson LP, Moore GE, Sojka JE
Correlation of Pituitary Histomorphometry with Adrenocorticotrophic Hormone Response to Domperidone Administration in the Diagnosis of Equine Pituitary Pars Intermedia Dysfunction
Vet Pathol 45:26–38 (2008)
AAEP Proceedings vol 52 2006
Domperidone Causes an Increase in Endogenous ACTH Concentration in Horses With Pituitary Pars Intermedia Dysfunction (Equine Cushing’s Disease)
Sojka JE, Jackson LP, Moore G, Miller M
Domperidone - Patrick McCue Colorado State University
It had been thought that a domperidone stimulation test might be a good diagnostic test for PPID. However Jill Beech compared ACTH measurements in 28 horses after domperidone administration and after TRH administration, and found that TRH stimulation gave more consistent results:
J Am Vet Med Assoc. 2011 May 15;238(10):1305-15.
α-Melanocyte--stimulating hormone and adrenocorticotropin concentrations in response to thyrotropin-releasing hormone and comparison with adrenocorticotropin concentration after domperidone administration in healthy horses and horses with pituitary pars intermedia dysfunction
Beech J, McFarlane D, Lindborg S, Sojka JE, Boston RC
"The change in ACTH concentration after domperidone administration was less consistent in differentiating clinically normal horses from those with PPID than was the response to TRH."
Miller MA, Pardo ID, Jackson LP, Moore GE, Sojka JE
Correlation of Pituitary Histomorphometry with Adrenocorticotrophic Hormone Response to Domperidone Administration in the Diagnosis of Equine Pituitary Pars Intermedia Dysfunction
Vet Pathol 45:26–38 (2008)
AAEP Proceedings vol 52 2006
Domperidone Causes an Increase in Endogenous ACTH Concentration in Horses With Pituitary Pars Intermedia Dysfunction (Equine Cushing’s Disease)
Sojka JE, Jackson LP, Moore G, Miller M
Donkeys and mules
The Donkey Sanctuary has information on the care and health of donkeys - www.thedonkeysanctuary.org.uk
Endocrine Disorders (Cushing's Disease and Equine Metabolic Syndrome) - The Donkey Sanctuary
Feeding the Donkey with Endocrine Disorders - The Donkey Sanctuary
(NB it is likely to be sugar in the grass, not fructan, that increases the risk of laminitis. In research, fructan has not increased insulin levels significantly.
Always check the sugar and starch content of bagged feeds with the manufacturer if this information is not on the bag/website - some High Fibre feeds contain sugar and starch levels in excess of 15% and are therefore unsuitable for equids with EMS/insulin dysregulation. Claims that feeds are suitable for laminitics or approved by laminitis charities should be ignored - always check the facts and figures, not marketing statements).
Thiemann AK, Buil J, Rickards K, Sullivan RJ
A review of laminitis in the donkey
Equine Veterinary Education 2021
Mendoza FJ, Toribio RE, Perez-Ecija A
Donkey internal medicine – Part I: metabolic, endocrine and alimentary tract disturbances
JEVS published online 07 Feb 2018
Endocrine blood testing for donkeys
Mendoza FJ, Buzon-Cuevas A, Toribio RE, Perez-Ecija A.
Characterisation of the oral glucose and sugar tolerance tests and the enteroinsular axis response in healthy adult donkeys.
Equine Vet J. 2022 Nov;54(6):1123-1132. doi: 10.1111/evj.13544. Epub 2021 Dec 21. PMID: 34897779.
Keywords: donkeys, glucose, horse, incretins, insulin dysregulation, metabolic syndrome
Mejia-Pereira S, Perez-Ecija A, Buchanan BR, Toribio RE, Mendoza FJ
Evaluation of dynamic testing for pituitary pars intermedia dysfunction diagnosis in donkeys
Equine Veterinary Journal 2019 51 481-488
Mendoza FJ, Mejia-Moreira S, Buchanan BR, Toribio RE, Perez-Ecija A
Evaluation of the combined glucose-insulin and intravenous glucose tolerance tests for insulin dysregulation diagnosis in donkeys
Equine Veterinary Journal 2021
Mejia-Moreira LS, Mendoza FJ, Buchanan B, Toribio RE, Perez-Ecija RA
Evaluation of Diagnostic Tests for Pituitary Pars Intermedia Dysfunction in Donkeys
International Equine Endocrine Summit Jan 2017
Results were in agreement with PPID guidelines for horses and support the use of baseline ACTH and TRH-stimulation for PPID diagnosis in donkeys.
Burden FA, Hazell-Smith E, Mulugeta G, Patrick V, Trawford R, Brooks HW
Reference intervals for biochemical and haematological parameters in mature domestic donkeys (Equus asinus) in the UK
Equine Veterinary Education 2016 28 (3) 134-139
A lack of transferability was noted between study parameters in donkeys and horses, and species-specific reference intervals for clinical assessment of veterinary cases should be used.
Medoza FJ, Perez-Ecija RA, Toribio RE, Estepa JC
Thyroid hormone concentrations differ between donkeys and horses
Equine Veterinary Journal 2013 45 214-218
Data gathered from Liphook Equine Hospital and The Donkey Sanctuary found that ACTH levels are not that different in donkeys compared to horses, so donkeys can have ACTH tested following the protocol for horses (Andy Durham Prascend webinar Feb 2012)
Díez E, López I, Pérez C, Pineda C, Aguilera-Tejero E.
Plasma leptin concentration in donkeys.
Vet Q. 2012;32(1):13-6. doi: 10.1080/01652176.2012.677867. Epub 2012 Apr 11. PMID: 22493943.
"Donkeys appear to have higher plasma leptin concentrations than horses and hyperleptinemia is correlated with BCS in donkeys."
BEVA Sept 2011
Adrenocorticotropic hormone in domestic donkeys - reference values, seasonality and association with laminitis
du Toit N, Shaw DJ and Keen JA
ACTH was measured in 422 donkeys admitted to The Donkey Sanctuary, UK. A distinct seasonality in ACTH was noted, with lower values Nov - June (median 17.8 pg/ml) than July - Oct (37.9 pg/ml) in non-obese & not laminitic donkeys. A reference range of 24.7 pg/ml was established.
BEVA Sept 2010
Insulin and ACTH values in donkeys with and without laminitis in the UK
du Toit N, Trawford AFand Keen JA
ACTH was measured in 126 donkeys admitted to The Donkey Sanctuary, UK.
Normal mean ACTH in non-obese donkeys without a history of laminitis 40.23 pg/ml
Mean ACTH levels in donkeys with a history of laminitis 51.73 pg/ml
Mean ACTH levels in donkeys without a history of laminitis 39.61 pg/ml
Mean ACTH levels in donkeys who developed clinical laminitis within a month of sampling: 46.58 pg/ml
Mean ACTH levels in donkeys who did not develop clinical laminitis within a month of sampling: 41.08 pg/ml
However no indication is given as to the month the blood samples were taken therefore it is not known whether the seasonal rise in ACTH was taken into account.
Susan L. Dugat, Tex S. Taylor, Nora S. Matthews, Jenifer R. Gold
Values for Triglycerides, Insulin, Cortisol, and ACTH in a Herd of Normal Donkeys
Journal of Equine Veterinary Science - March 2010 (Vol. 30, Issue 3, Pages 141-144, DOI: 10.1016/j.jevs.2010.01.054)
Medicines
Lizarraga I, Sumano H, Brumbaugh GW
Pharmacological and pharmacokinetic differences between donkeys and horses
Equine Veterinary Education 2004 16 (2) 102-112
Discussion: important differences in pharmacokinetcis and pharmacodynamics exist between horses and donkeys, and among breeds of donkeys. Direct extrapolation of dosage regimens for horses to use in donkeys may impose some danger to the latter species. The donkey should not be regarded as a small odd-looking horse, but should be recognised and treated as a species in its own right. Donkeys have a relative greater capacity than horses to metabolise and/or eliminate (some) drugs, e.g. clearance of phenylbutazone in donkeys is about 5- to 15-fold greater than in horses. For some drugs that undergo hepatic metabolism, the dose and dosing-interval used for horses may not be appropriate for donkeys.
Grosenbaugh DA, Reinemeyer CR, Figueiredo MD
Pharmacology and therapeutics in donkeys
Equine Veterinary Education 2011 23 (10) 523-530
Hyperlipaemia
Donkeys are particularly susceptible to hyperlipaemia (usually caused if the donkey stops eating for any reason).
What do you know about hyperlipaemia? - The Donkey Sanctuary
Feet
Nocera I, Aliboni B, Ben David L, Gracia-Calvo LA, Sgorbini M, Citi S.
Radiographic and Venographic Appearance of Healthy and Laminitic Feet in Amiata Donkeys.
Front Vet Sci. 2020 Dec 21;7:601665. doi: 10.3389/fvets.2020.601665. PMID: 33409297; PMCID: PMC7779588.
Collins SN, Dyson SJ, Murray RC, Newton JR, Burden F, Trawford AF
Development of a quantitative multivariable radiographic method to evaluate anatomic changes associated with laminitis in the forefeet of donkeys
Am J Vet Res. 2012 Aug;73(8):1207-18. doi: 10.2460/ajvr.73.8.1207
Collins SN, Dyson SJ, Murray RC, Burden F, Trawford A
Radiological anatomy of the donkey's foot: objective characterisation of the normal and laminitic donkey foot
Equine Vet J. 2011 Jul;43(4):478-86. doi: 10.1111/j.2042-3306.2010.00312.x (access to images - Semantic Scholar)
Notes: donkeys have prominent coronary bands which can make palpation of supracoronary depression difficult.
Donkeys may not show signs of pain until advanced laminitic changes have take place.
LM radiographs (x-rays) are very important for diagnosing laminitic changes. It is essential to know what is normal. Clinical signs of (chronic) laminitis in the feet include divergent hoof rings (wider at the heels than at the toe), stretched white line, flat sole, bruising on the sole beneath the pedal bone, change in hoof angle/flared toe.
X-rays were taken with both (front) feet on 8 cm wooden blocks with a wire groundline, with the limb evenly weightbearing and the canon bone vertical, the heel bulbs perpendicular to the cassette. The x-ray beam was focused midway between the dorsal and palmar aspects of the foot and midway between the coronary band and the top of the block,80 cm from the cassette.
The paper suggests that the degree of bone remodeling is particularly significant in donkeys (but no reference given).
Normal donkey feet had a hoof wall at the toe nearly parallel to the dorsal aspect of P3 (a difference of 2.5 degrees), and a very slightly broken hoof pastern axis (but with considerable variation).
It should be noted the same farrier trimmed all the feet.
Clinical Companion of the Donkey - The Donkey Sanctuary (for professionals) - chapter 9 on feet and laminitis.
Guidelines for the management of farmed donkeys - Nutrition: food and water - The Donkey Sanctuary 2020
Donkey Hoof Care - The Donkey Sanctuary (for owners)
Natural Equine Hoof Care - Donkey and Mule Hooves slideshow
HoofSearch complete index of online donkey hoof-related references published from 1977 to May 2020
Webinar: What's different about donkeys? Donkeys and laminitis - with Alex Thiemann, Senior Veterinary Surgeon at The Donkey Sanctuary.
Some key points:
Donkeys gain weight easily and need around 30% less energy than a similar weight pony
Donkeys should be fed differently to ponies.
Treat inappetance seriously - this can lead to fatal hyperlipaemia.
Make diet changes slowly.
Know your donkey and learn to recognise signs of pain.
Donkey hooves differ from horse hooves.
Use donkey normal values for x-ray interpretation.
Heart bar shoes are not useful for donkeys.
White line disease, thrush, abscesses are common alongside laminitis.
Signs of laminitis can be more subtle in donkeys than horses. You may see increased lying down, increased digital pulses, stiff pottery gait, struggle to turn, posture changes and changes in the hooves (in chronic laminitis).
If a donkey has laminitis: a vet should carry out a detailed examination and assess the level of pain. X-rays should be taken at an early stage to guide prognosis [to guide realigning trimming]. Pain relief given should be specific to donkeys (donkeys metabolise NSAIDs more quickly than horses so may need 2 x day dosing). Keep the donkey's companion close and ensure the donkey continues to eat.
TLS: NB endocrinopathic laminitis rarely involves significant inflammation.
Some key points:
Donkeys gain weight easily and need around 30% less energy than a similar weight pony
Donkeys should be fed differently to ponies.
Treat inappetance seriously - this can lead to fatal hyperlipaemia.
Make diet changes slowly.
Know your donkey and learn to recognise signs of pain.
Donkey hooves differ from horse hooves.
Use donkey normal values for x-ray interpretation.
Heart bar shoes are not useful for donkeys.
White line disease, thrush, abscesses are common alongside laminitis.
Signs of laminitis can be more subtle in donkeys than horses. You may see increased lying down, increased digital pulses, stiff pottery gait, struggle to turn, posture changes and changes in the hooves (in chronic laminitis).
If a donkey has laminitis: a vet should carry out a detailed examination and assess the level of pain. X-rays should be taken at an early stage to guide prognosis [to guide realigning trimming]. Pain relief given should be specific to donkeys (donkeys metabolise NSAIDs more quickly than horses so may need 2 x day dosing). Keep the donkey's companion close and ensure the donkey continues to eat.
TLS: NB endocrinopathic laminitis rarely involves significant inflammation.
Dopamine (DA)
In the healthy horse, dopamine inhibits the production of hormones from the pars intermedia. Dopamine is released into the pars intermedia from dopaminergic neurons (tuberoinfundibular dopamine neurons) that originate in the hypothalamus. The dopamine binds to dopamine (D2) receptors on the surface of the melanotropic cells of the pars intermedia, rather like putting a key in a lock. Once the dopamine is bound to the receptor, the production and release of POMC hormones (α-MSH, β-endorphin, CLIP and ACTH) is inhibited.
PPID is considered to be a dopaminergic neurodegenerative disease - the lack of sufficient dopamine leads to increased POMC hormone production and release. The reduction in dopamine also causes hyperplasia and hypertrophy of the cells of the pars intermedia, leading to adenomas and causing the pars intermedia to increase in size.
Dopamine also inhibits prolactin, growth hormone (GH) and thyroid-stimulating hormone (TSH) secretion in the pars distalis.
Dopamine and dopamine agonists (Pergolide, Bromocriptine) inhibit POMC secretions from the pars intermedia (Orth et al 1982).
Vet Clin North Am Equine Pract. 2011 Apr;27(1):1-17
Hypothalamic-pituitary gland axis function and dysfunction in horses
Hurcombe SD
McFarlane D, Donaldson MT, Saleh TM, Cribb AE
The Role of Dopaminergic Neurodegeneration in Equine Pituitary Pars Intermedia Dysfunction (Equine Cushing's Disease)
AAEP 49th Convention 2003
Horses with PPID had a 5-fold reduction in the number of dopaminergic terminals in the pars intermedia compared to age controls.
Dopamine - A Sample Neurotransmitter - www.utexas.edu
PPID is considered to be a dopaminergic neurodegenerative disease - the lack of sufficient dopamine leads to increased POMC hormone production and release. The reduction in dopamine also causes hyperplasia and hypertrophy of the cells of the pars intermedia, leading to adenomas and causing the pars intermedia to increase in size.
Dopamine also inhibits prolactin, growth hormone (GH) and thyroid-stimulating hormone (TSH) secretion in the pars distalis.
Dopamine and dopamine agonists (Pergolide, Bromocriptine) inhibit POMC secretions from the pars intermedia (Orth et al 1982).
Vet Clin North Am Equine Pract. 2011 Apr;27(1):1-17
Hypothalamic-pituitary gland axis function and dysfunction in horses
Hurcombe SD
McFarlane D, Donaldson MT, Saleh TM, Cribb AE
The Role of Dopaminergic Neurodegeneration in Equine Pituitary Pars Intermedia Dysfunction (Equine Cushing's Disease)
AAEP 49th Convention 2003
Horses with PPID had a 5-fold reduction in the number of dopaminergic terminals in the pars intermedia compared to age controls.
Dopamine - A Sample Neurotransmitter - www.utexas.edu
Dopamine agonists
Pergolide is a dopamine agonist used to treat PPID in horses.
Arana Valencia N, Thompson Jr DL, Oberhaus EL
Long-term and Short-term Dopaminergic (Cabergoline) and Antidopaminergic (Sulpiride) Effects on Insulin Response to Glucose, Glucose Response to Insulin, or Both in Horses
Journal of Equine Veterinary Science Volume 59, December 2017, Pages 95-103
"We conclude that dopaminergic agents have no benefit for treating insulin insensitivity in horses, in spite of a perception of such benefits permeating the industry."
Use of dopamine agonists in other species - NB effects mentioned may not be the same for horses:
Borovaca JA
Side effects of a dopamine agonist therapy for Parkinson’s disease: a mini-review of clinical pharmacology
Yale J Biol Med. 2016 Mar; 89(1): 37–47
Ceravolo R, Rossi C, Del Prete E, Bonuccelli U
A review of adverse events linked to dopamine agonists in the treatment of Parkinson's disease
Expert Opin Drug Saf. 2016;15(2):181-98. doi: 10.1517/14740338.2016.1130128. Epub 2016 Jan 20
Pergolide is a dopamine agonist used to treat PPID in horses.
Arana Valencia N, Thompson Jr DL, Oberhaus EL
Long-term and Short-term Dopaminergic (Cabergoline) and Antidopaminergic (Sulpiride) Effects on Insulin Response to Glucose, Glucose Response to Insulin, or Both in Horses
Journal of Equine Veterinary Science Volume 59, December 2017, Pages 95-103
"We conclude that dopaminergic agents have no benefit for treating insulin insensitivity in horses, in spite of a perception of such benefits permeating the industry."
Use of dopamine agonists in other species - NB effects mentioned may not be the same for horses:
Borovaca JA
Side effects of a dopamine agonist therapy for Parkinson’s disease: a mini-review of clinical pharmacology
Yale J Biol Med. 2016 Mar; 89(1): 37–47
Ceravolo R, Rossi C, Del Prete E, Bonuccelli U
A review of adverse events linked to dopamine agonists in the treatment of Parkinson's disease
Expert Opin Drug Saf. 2016;15(2):181-98. doi: 10.1517/14740338.2016.1130128. Epub 2016 Jan 20