<i>Ex Vivo</i> Fermentation of Hay and Corn by Rumen Bacteria from Cattle and Sheep

Sheep are often utilized as a model ruminant, despite a lack of functional comparisons of rumen bacterial communities and responses during dietary transitions between sheep and cattle. Therefore, an <i>ex vivo</i> study was conducted to evaluate species differences. Rumen fluid was obtained from hay-fed sheep and cattle (<i>n</i> = 3 species⁻¹). Mixed bacterial cell suspensions in buffered media containing 3% <i>w</i>/<i>v</i> ground hay, corn, or combinations (2:1, 1:2) of substrates were incubated (24 h; 39 °C). Suspension pH, lactate, volatile fatty acids (VFA), and digestibility were assessed, functional guilds enumerated, and amylolytic bacteria isolated. Lactate was fully utilized in all hay incubations, and pH did not differ between species (<i>p</i> > 0.75). In contrast, digestibility, lactate accumulation, and pH decline were greater in bovine suspensions fermenting corn (<i>p</i> < 0.01). <i>Streptococcus bovis</i> was the predominant bacteria regardless of species, but total amylolytic bacteria were 10-fold greater in bovine suspensions (<i>p</i> < 0.01). Lactate-utilizing bacteria were 1000-fold greater in bovine than ovine suspensions (<i>p</i> < 0.01). However, total VFA did not differ between species (<i>p</i> > 0.28). Overall, these results demonstrate differential feed utilization capacities in rumen microbial communities of sheep and cattle as well as potential differences in rumen acidosis susceptibility.