Vet Edd Knowles, currently at Bell Equine, completed his PhD at the RVC in 2021.  His research showed that testing insulin, both resting and after an oral sugar test using Karo Light corn syrup, was the best way to identify ponies that would develop laminitis.  Other factors identified by Knowles that can help identify horses at risk of laminitis include level of exercise, body condition score/body fat and hoof changes - although hoof changes (related to laminitis such as divergent hoof rings) will follow laminitis, not precede it.

Knowles' research was published in the EVJ September 2021 special issue for BEVA 2021 clinical research abstracts:
​Knowles EJ, Elliott J, Harris PA, Menzies-Gow NJ
Predictors of laminitis development in non-laminitic ponies
Equine Veterinary Journal August 2021 Vol 53 Issue S55 Clinical Research Abstracts of the BEVA Congress 2021​ p21-22.  https://doi.org/10.1111/evj.31_13492

and as a full paper in the EVJ in March 2022:
​Knowles EJ, Elliott J, Harris PA, Chang YM, Menzies-Gow NJ.
Predictors of laminitis development in a cohort of non-laminitic ponies.
Equine Vet J. 2022 Mar 9. doi: 10.1111/evj.13572. Epub ahead of print. PMID: 35263471.

374 ponies were monitored for up to 4 years (giving 891 pony years - 891 pony years/374 ponies = an average of 2.4 years that a pony was followed for).  The ponies were considered non-laminitic when they entered the study.  Every 6 months blood was collected for measurement of basal ACTH, adiponectin, triglycerides, glucose and basal non-fasted insulin (T0), and an oral sugar test was carried out 60 minutes (T60) after administering 0.3 ml/kg bodyweight (rather than the standard 0.15 or 0.45 ml/kg) Karo Light corn syrup.  Insulin was measured using a Tosoh AIA-360 Fluorescence Enzyme Immunoassay.

4.8 ponies developed laminitis per 100 pony years, or per 100 ponies/year.  The ponies were divided into 3 groups - low, medium and high risk of laminitis depending on their basal T0 and 60 minutes after Karo Light corn syrup (T60) insulin results.

Measured factors that were associated with the development of laminitis included basal insulin, insulin 60 minutes after giving Karo Light corn syrup, adiponectin, and evidence of divergent hoof growth.  Divergent hoof rings are a sign of chronic laminitis - at The Laminitis Site we have only seen divergent hoof rings where there is palmar rotation and usually (at least at some point) dorsal rotation and signs of compression in the toe wall/coronary band, therefore we would argue that seeing divergent hoof rings shows that a pony has already had laminitis, and is not predictive of future laminitis.  Seeing divergent hoof rings means that x-rays should be taken to assess and guide the realignment of rotation/misalignment between pedal bone and hoof capsule.

ACTH was not associated with laminitis.

The 3 risk groups were:
Low: non-fasted basal insulin <21.6 uIU/ml, 70% of the population were in this group, so 261.8/374 ponies, incidence of laminitis was 6% in this group over 4 years.
Medium: non-fasted basal insulin 21.6-45.2 uIU/ml, 20% of the population were in this group, so 74.8/374 ponies, incidence of laminitis was 22% in this group over 4 years.
High: non-fasted basal insulin >45.2 uIU/ml, 10% of the population were in this group, so 37.4/374 ponies, incidence of laminitis was 69% in this group over 4 years.


Under Main limitations the abstract says "Results may not apply to different insulin assays...".

Questions:
How does the Tosoh AIA-360 Fluorescence Enzyme Immunoassay compare e.g. to Immulite 2000 results?  Was this assay validated for equine insulin?  
What did the ponies eat before their basal non-fasted insulin blood collections?

Listen to The Humble Hoof's podcast Laminitis: Treatment and Prevention with Dr Alicia Nolfi.  Dr Nolfi discusses laminitis treatment, and the importance of preventative care.

Laminitis: Treatment and Prevention Podcast

The link between insulin dysregulation, obesity and laminitis in horses - Prof. Simon Bailey, University of Melbourne

Webinar: How to provide a good life for horses: friends, freedom and forage
Hosted by World Horse Welfare on 26 May 2021

The Latest on EMS, PPID & Laminitis
Webinar by Jamie Prutton from Liphook Equine Hospital and Tracey Hammond from Dengie Horse Feeds on 31 March 2021, hosted by Dengie Horse Feeds

Dengie brought out a new Laminitis Guide in March 2020, which features photos taken by The Laminitis Site of some of the many laminitis cases that TLS has helped.  Dengie very kindly provided The Laminitis Site with Dengie feed vouchers as a thank you - for which rescued laminitic pony Dolly will be very pleased, as she loves Dengie HiFi molasses free!

The researchers concluded that supplementation with a mixture of straw and hay is a safe, cost-effective means of supporting weight loss in grazing ponies kept in groups.

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If feeding straw:
Ensure teeth have been checked and function well.
Introduce straw gradually, as with all feeds.
Feed barley or oat straw, ideally not sprayed with chemicals and of good hygienic quality.
Feed no more than 50% of the total forage amount as straw.  NB Pat Harris suggests feeding no more than 25% of the total forage amount as straw.

Laminitis is generally treated and managed by:
1 restricting movement, pain relief and supporting the feet,
2 therapeutic trimming [TLS would argue that shoeing is almost never the best option, and realigning trimming should be part of the initial care], and diagnosis/treatment/management of hormonal disorders,
3 ongoing management of the horse's diet, exercise and footcare.

Laminitis prevention:
​WHW suggest that important risk factors for laminitis include recent weight gain, a history of laminitis and foot soreness after shoeing/trimming.  Ensuring a horse is not overweight is very important for preventing laminitis.  A history of laminitis tells you that they almost certainly have a hormonal condition (EMS / PPID) that needs to be managed/treated, and chronic laminitis to be corrected.  Foot soreness after shoeing/trimming is often seen in horses that have had laminitis that haven't had their feet correctly realigned and supported/protected - often it is foot pain from chronic (uncorrected) laminitis that is seen when horses appear to have recurrent, and not necessarily new laminitis (linked to abnormal hormone production).

The proceedings from the Global Equine Endocrine Symposium held in Germany in January 2020 are available here.

The Horse published 2 articles about feet in December 2019:

Horse Hoof Anatomy, Part 1 - Christy West, www.thehorse.com, Dec 2019
The angle between the bottom (solar) surface of the coffin bone and the front of the bone is usually around 50 degrees, but it can be steeper (usually in a club foot) or flatter (usually in a long-toe, low-heeled foot). The coffin bone can fracture and remodel significantly in response to stress. Loss of the distal rim (toe edge) of the coffin bone can occur if there isn’t much foot or sole mass (for shock absorption and protection); this can be secondary to (caused by) poor foot growth, lack of sole thickness/protection, or club foot.

"The palmar angle, between the bottom or wings of the coffin bone and the ground, can be a significant indicator of foot health. For example, a normal palmar angle is slightly positive (heels slightly higher than the toe). But Rucker says an angle higher than 10° suggests the club foot is severe or laminitis has caused instability of the bone within the hoof (and severe laminitis can cause coffin bone breakdown starting at the rim and even significant loss of bone mass).  Conversely, a zero or negative palmar angle (heels lower than the toe) suggests that the foot has crushed heels and a compromised digital cushion." 

The collateral (or lateral) cartilages extend upward from either side of the coffin bone and help the hoof expand with weight bearing.  Ossification of the collateral cartilages can limit the hoof’s natural expansion and result in some sensitivity to touch via hoof testers.  Lameness isn't always seen, and this is most commonly seen in heavy horses working on hard ground.

The digital cushion lies below the coffin bone and above the frog and cushions the foot from ground forces. When a horse has a broken back hoof pastern angle and/or long toe/low heels and the heels are over-loaded, the digital cushion is crushed.  Stephen O'Grady says "The most common problem I see in internal hoof structures is poor heel structure and inadequate sole depth (due to digital cushion loss)”.

Between the coffin bone and the hoof wall lies the corium - soft tissue that includes blood vessels, nerves, and the laminae—interlocking leaflike structures that attach the hoof to the bone. If a disease or trauma causes swelling in the hoof, the hoof can’t expand to accommodate both the swelling and the blood flow, and swelling generally wins. Without blood flow, tissue and bone can die. Laminitis is disease of the laminae that can range from mild to severe and transient to chronic, often caused by metabolic problems like Equine Metabolic Syndrome and PPID (in both cases insulin dysregulation leads to laminitis).  The laminae can detach and the coffin bone rotate away from and sink down within the hoof capsule.

Hoof Trimming to Improve Structure and Function - notes from Robert Bowker 2019 NEAEP Symposium, Stephanie Church, www.thehorse.com, Dec 2019
Dr Robert Bowker, longtime podiatry researcher and former professor and head of the Equine Foot Laboratory at Michigan State University’s (MSU) College of Veterinary Medicine, described his perspectives and trimming approaches during a presentation at the Septenber 2019 NEAEP symposium.

The foot should be balanced approximately 50:50 toe:heel, so that if a perpendicular line is dropped from the center of rotation of the short pastern bone (P2), half the foot is in front of the line and half behind.

Bowker seems many cases with chronic periodic lameness in both front feet, that have long toes and underrun heels.  When the toe is long, i.e. more foot is in front of the perpendicular line than behind, pressure is put on the coffin joint, eventually leading to navicular disease.  In these long-toed feet, the coffin bone changes shape and gets longer, reducing bone density, and the blood supply changes, with increased blood supply to the front of the foot, to the detriment of the back of the foot and the frog. Bowker says that feet with long toes and underrun heels are probably the most likely to develop navicular, and will suffer more if they develop laminitis. “With a long-toe, underrun heel, the tissues supporting and surrounding the coffin bone become compromised and the distal (bottom) end of the coffin bone gets less and less support and becomes thinner and thinner along the edges, especially the lateral (away from the midline) side of the foot. These changes will often result in pedal osteitis". 

​When a horse with peripheral thinning of P3 gets laminitis and rotation, the bone cannot support the weight of the horse and becomes crushed.  

Bowker trims to shorten the toe, trimming inside the white line if necessary, and promote caudal (toward the rear) migration of the heels to bring the central sulcus (the cleft between the heels) back to the sole of the foot so it makes light contact with the ground. He said trimming with these goals can improve the foot’s health and get the ratio to approach 40:60—allowing the back part of the foot to enlarge and return to its robust health.

To correct a long toe/underrun heels foot:
Bring the heels back to the level of (back of) the frog, and so that the frog just kisses the ground - too much pressure reduces the blood supply and causes the frog to atrophy.
The frog's central sulcus should be wide and shallow, and ideally the frog should not be trimmed, as trimming causes the frog to retract and reducees its ability to dissipate energy [however the frog may need to be trimmed if heels need to be lowered].
Bevel the toe from beneath (the sole), not the outside (dorsal hoof wall), trimming inside the white line every few days to keep the toe short.
Trim the foot initially every 3-4 days until the toes and heels are back under the horse, then the trim interval can be lengthened to up to 4 weeks (less when feet are growing quickly). 
Measure the feet every 3-4 days to monitor changes.

​Bowker has been able to improve digital cushions despite wide acceptance that digital cushion damage is permanent (it isn't) - he says "internal changes can occur if the farrier or trimmer gives the foot an opportunity.  A crushed digital cushion will repair itself with myxoid cells", and "you can always improve the trim to improve the internal structure of the tissues.  If you have a short toe, you'll have a pretty good foot".

"Here are some insights and tips Bowker shared on the normal equine foot and what goes wrong with typical husbandry practices:
1. The foot is extremely adaptable. Conformation is a point in time. This can be corrected and improved if the foot is given the opportunity.
2.  The foot adapts to the environment (trimming, shoeing, loading, ground surface, moisture, etc.), but the biggest environmental factors are the hoof care professional and the trim. “They can cause major environmental effects and greater biomechanical changes in a brief time period. These changes affect the internal tissues—they respond each time the foot is trimmed.”
3.  All feet are different, even in the same horse and in the same pair of legs.
4.  Long toes and underrun heels are ubiquitous, and much of the horse industry accepts them as normal. “I have several thousand sagittal photos of feet … (only) one of them is (balanced) 50:50 front to back,” he said.
5.  As the toe and coffin bone lengthen, Bowker says the coffin bone remodels internally as it attempts to support the longer toe; the bone becomes more porous due to more movement between the bone and hoof wall. “This increased porosity is not beneficial”.
6.  Navicular bone movement up and down, due to the changes in foot mechanics, damages the deep digital flexor tendon, as well as insertion ligaments of the distal sesamoidean impar ligament.
7.  With long-toe, underrun heels, the bottom end of the short pastern (P2) changes shape, too. It starts out symmetrical in its articulation with the coffin bone. But current standard trimming methods alter the biomechanics, as the ends of P2 become asymmetrical. “With the gradually increasing length of the coffin bone, chip fractures begin to appear on the navicular bone, and they can appear (at any age). Many associate these fractures with navicular syndrome. If you have a short toe, you don’t have that.”"