Abstract
Starch/grain intake has been reported to be at risk for equine gastric lesions of the squamous mucosa (Equine Squamous Gastric Disease – ESGD). Exposition to VFAs and lactic acid, end-products of the fermentation occurring in the gastric ecosystem, can cause ESGD. As in the hindgut, supplementing yeast to high starch/grain diet could increase lactate-utilizing bacteria and thus limit the production of lactic acid and eventually the acidity. The objective of this study was to investigate the effect of two levels of Saccharomyces cerevisiae (Sc47) supplementation on gastric ecosystem in horses fed high-starch diet.Six horses were assigned in a 3*3 Latin square design with three supplement treatments: 10.109 (dose 1) or 10.1010 (dose 10) cfu of zootechnical additive Sc47 per day or a control. Each experimental period lasted 21 days and was separated from the next one by a wash-out period of 21 days. During experimental periods, horses received a 70:30 ratio hay:barley (2.3kg DMI / 100kg BW / day) and 50g per day of the additive. Gastric content samples were collected on day 18 of each experimental period 3h and a half after morning barley meal to measure: pH, bacterial populations (total anaerobic, amylolytic and lactate-utilizing bacteria), and fermentation products (VFAs and lactic acid).The observation of the stomach with the video-endoscope did not reveal any alteration of the squamous gastric mucosa. Total anaerobic bacteria and amylolytic concentrations were lower with Sc47 dose 10 compared to placebo (P = 0.03 and 0.04, respectively). With dose 10 of Sc47, lactate-utilizing bacteria concentrations decreased compare to Sc47 dose 1 (P = 0.03) and placebo (P = 0.004). No treatment effect was observed on total VFAs and lactic acid concentrations. Butyric and valeric acids concentrations showed higher concentration with Sc47 dose 1 compared to other treatments during period 1. Although, the pHs were numerically less acidic with live yeast, they were not significantly modified by the treatment. Globally, there was a dose effect of Sc47 on bacteria concentrations which all decreased or tended to decrease when the level of yeast increased in the diet. Further investigation is required to know whether live yeast supplementation could be part of the strategy to reduce gastric fermentation of starch and thereby help reducing the risk of ESGD.
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