Effect of inoculation of laminitic-prone, equine faecal inocula with varying forage sources with or without live yeast (Saccharomyces cerevisiae) on in vitro gas production parameters

It is widely accepted that inclusion of live yeast in equine diets can increase numbers of fibrolytic bacteria in the hindgut and thus increase overall digestibility of the diet and a more stable hindgut environment. Additionally, it is recognised that horses suffering from laminitis may have impaired hindgut activity and may benefit from dietary yeast inclusion. Little work has been carried out examining the effects of adding live yeast to forage-only diets in the horse. The aim of this study was to examine the effects on fermentation of the addition of live yeast to varying forage sources using the in vitro gas production technique and using inocula from laminitic horses. Four different forage sources: hay (H), haylage (Hy), red clover silage (RCS) and dried lucerne chop (LC) were incubated in triplicate with or without the addition of live yeast. Substrates were subjected to a pepsin pre-treatment and the extent and rate of degradation were then measured using the gas production technique. Three hundred mg of dried forage were incubated with 30 ml of faecal inocula from laminitic-prone horses with or without 1 mg of live yeast and gas production measured over 96 h. VFA were determined using gas chromatography. Fermentation kinetics were fitted to the model p = a + b (l – e-ct). Mean gas production at 96 h was significantly (P<0.001) increased in all forages following the inclusion of yeast. There was no significant effect on acetate, propionate or n-butyrate. Addition of live yeast to faeces from laminitic-prone horses increased the gas production over mean retention time from all forages. This may be suggestive of increased fibrolytic and lactate-utilising bacterial activity and could potentially prove beneficial for laminitic horses. Further work is needed to establish the full effect of yeast on fibre digestibility and fermentative capacity in vivo in laminitic horses.