Effect of starch source (corn, oats or wheat) and concentration on fermentation by equine faecal microbiota in vitro

Aims: The goal was to determine the effect of starch source (corn, oats and wheat) and concentration on: (i) total amylolytic bacteria, Group D Gram-positive cocci (GPC), lactobacilli and lactate-utilizing bacteria, and (ii) fermentation by equine microbiota. Methods and Results: When faecal washed cell suspensions were incubated with any substrate amylolytics increased over time. However, at 24 h there were 10 and 1000-fold more amylolytics with corn than wheat or oats respectively. Predominant amylolytics isolated were Enterococcus faecalis (corn, wheat) and Streptococcus bovis (oats). GPC increased with any substrate, but decreased during stationary phase in oats only. Lactobacilli decreased during stationary phase with corn only. By 24 h, oats had more lactate-utilizers and lactobacilli and fewer GPC than corn and wheat. More gas was produced from oats or wheat than from corn. Conclusions: These results indicate that the growth of bacteria and fermentative capacity associated with starch metabolism is starch source dependent. Significance and Impact of the Study: This study demonstrates a relationship between starch source and microbial changes independent of host digestion. However, future research is needed to evaluate the effect of starch source on the hindgut microbial community in vivo.