Inhibition of fructan-fermenting equine faecal bacteria and Streptococcus bovis by hops (Humulus lupulus L.) β-acid
Harlow BE1, Lawrence LM, Kagan IA, Flythe MD
"AIMS:The goals of this study were to determine if β-acid from hops (Humulus lupulus L.) could be used to control fructan fermentation by equine hindgut micro-organisms, and to verify the antimicrobial mode of action on Streptococcus bovis, which has been implicated in fructan fermentation, hindgut acidosis and pasture-associated laminitis (PAL) in the horse.
METHODS AND RESULTS:Suspensions of uncultivated equine faecal micro-organisms produced fermentation acids when inulin (model fructan) was the substrate, but β-acid (i.e. lupulone) concentrations ≥9 ppm inhibited lactate production and mitigated the decrease in pH. Inulin-fermenting Strep. bovis was isolated from the β-acid-free suspensions after enrichment with inulin. The isolates were sensitive to β-acid, which decreased the viable number of streptococci in faecal suspensions, as well as growth, lactate production and the intracellular potassium of Strep. bovis in pure culture.
CONCLUSIONS:These results are consistent with the hypothesis that hops β-acid prevented the growth of fructan-fermenting equine faecal bacteria, and that the mechanism of action was dissipation of the intracellular potassium of Strep. bovis.
SIGNIFICANCE AND IMPACT OF THE STUDY:Bacterial hindgut fermentation of grass fructans has been linked to PAL and other metabolic disorders in horses. Hops β-acid is a potential phytochemical intervention to decrease the growth of bacteria responsible for PAL."
This abstract should be read in conjunction with:
Journal of Equine Veterinary Science 33 (2013) 321-399
Effects of hops (Humulus lupulus L.) beta-acid extract on inulin fermentation by equine fecal microflora in vitro
BE Harlow, LM Lawrence, MD Flythe
Presented at the Equine Science Society Symposium 2013
There are currently thought to be three types of laminitis:
Endocrine laminitis probably accounts for ~90% of all cases of laminitis (Karikoski et al. 2011). Pasture associated laminitis (PAL) is endocrine. Sugars in the grass cause insulin to rise in some horses, i.e. horses with an underlying hormonal dysfunction - insulin resistance or hyperinsulinaemia. As far as we know at the moment, fructans do not increase insulin levels (Borer et al. 2012), therefore they are very unlikely to be involved in causing PAL. Horses with PAL have raised insulin, and/or symptoms of EMS.
In research, huge amounts of inulin (a short-chain fructan which is not found in significant quantities in the horse's natural diet) have been pumped directly into a horse's stomach. This has caused acidosis and led to SIRS laminitis. Equivalent amounts of fructan cannot be eaten naturally, even by the greediest horse - and even if it could, it would be over 24 hours, not in 5 minutes. With SIRS laminitis, the horse always has a significant primary illness, laminitis is secondary, and the horse will have changes in white blood cells and lactate, usually a raised temperature and usually diarrhoea. These symptoms are not seen with PAL.
So any research looking to reduce the fermentation of fructan to lactate and thereby reduce the incidence of acidosis has no relevance, as far as we know at the moment, for pasture associated laminitis.
It could have relevance for starch overload laminitis, which is SIRS laminitis.
Going through the second abstract:
Brittany Harlow claims that "the ingestion of large quantities of fructan or other rapidly fermentable carbohydrates has been associated with the development of laminitis". Starch yes, naturally ingested fructans, no.
She claims that this can lead to proliferation of Gram-positive bacteria, leading to increased lactic acid production and acidosis. Again starch, yes, naturally ingested fructan, no. And that antibiotics e.g. Founderguard can be used to reduce this gut disturbance. True - Founderguard may be useful when given in advance of high amounts of starch being fed, but not grass - Founderguard has no beneficial action on reducing insulin.
The research into the use of hops has basically come about because Founderguard, an antibiotic, cannot be used frequently and probably shouldn't be used at all (it's a preventative, not a cure) - we are all rightly worried about antibiotic resistance from the over-use of antibiotics. So an alternative that doesn't raise concerns about antibiotic resistance might be a great idea. True - for horses that continue to be fed large amounts of cereal. How about just not feeding them large amounts of cereal in the first place?
The study took 3 horses who were eating alfalfa hay and grass. The abstract doesn’t give figures for the fructan or sugar content of the hay or grass. Presumably the research was carried out in Kentucky, which is latitude 38 (compared to London 51). Research suggests that C3 dominance changes to C4 at latitude 42-45, but the famous Kentucky blue grass is C3, and other research suggests quite a mix of C3 and C4 in Kentucky. So there was probably less fructan in the grass than we'd see in the UK, but there will have been some (C3 stores excess carbs as fructan, C4 doesn't). These horses were presumably healthy and managing to eat naturally occurring fructan with no problem, and no decrease in dung pH.
The researchers collected dung from these horses, separated bacteria from it and mixed the bacteria with inulin, then added hop extract to some of the samples and incubated them for 24 hours.
Just how relevant is looking at the bacteria in dung compared to the bacteria inside the horse? Is it likely that the "bad" lactic acid producing bacteria would be higher in dung than inside the horse?
The samples with only inulin added became more acidic and had higher lactic acid concentrations. Adding hop extract at 180 ppm (mg/kg) or higher reduced this acidity. We're told that after 21 hours the samples with 150 (I think this should say 180) ppm hop extract added had a pH of 6.2 (in the 0.1% inulin sample - without hop extract pH was 5.5) and 5.5 (in the 0.6% inulin sample - without hop extract pH was 3.7). We're not told what the pH of the original dung was, and no control of bacteria with nothing (no inulin, no hop extract) added was used.
Volatile Fatty Acid concentrations were also measured and were found to increase with increasing hop extract amounts in the 0.6% inulin sample. This is quite interesting, because I have seen suggestions that fructans are only fermented to lactate, and not to VFAs as they should be (it seems obvious to me that horses are quite happily fermenting fructan to VFAs, given that millions of horses are happily eating grass, getting fat and not getting acidosis or laminitis). VFA production figures aren't given, but the only/main substrate for fermentation is presumably the inulin, so this suggests that inulin is fermented by bacteria in/from the horse's gut to VFAs. Treatment with hop extract increased VFA production and reduced lactate production.
This suggests that hop extract could reduce lactic acid producing bacteria without compromising VFA producing bacteria. So this may be useful research for the very few cases of SIRS laminitis caused by planned cereal overload - but there is nothing to suggest that it can help pasture associated laminitis cases.
I haven't read the full paper - if anyone has, I'd be interested in your comments.
See Do fructans cause laminitis?
Also, have a look at this review of the paper by Kathleen, Director and Research Advisor of the ECIR group in December 2014 - What's the harm. Why associations should be questioned.
Borer KE, Bailey SR, Menzies-Gow NJ, Harris PA, Elliott J
Effect of feeding glucose, fructose, and inulin on blood glucose and insulin concentrations in normal ponies and those predisposed to laminitis
J Anim Sci. 2012 May 14 [Epub ahead of print]
Karikoski NP, Horn I, McGowan TW, McGowan CM
The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital.
Domest Anim Endocrinol. 2011 Jun 7