Effects of different protein sources on nutrient disappearance, rumen fermentation parameters and microbiota in dual-flow continuous culture system

Scarce high-quality protein feed resources has limited the development of animal husbandry. In this study, we used a dual-flow continuous culture system to evaluate effects of difference dietary protein sources including soybean meal (SBM), cottonseed meal (CSM), and rapeseed meal (RSM), on nutrient disappearance, rumen fermentation, and microbiota of XiongDong black goats. Dietary proteins of either CSM, RSM or SBM had no effect on nutrient disappearance (P > 0.05). CSM or RSM significantly reduced (P < 0.01) the pH and enhanced (P < 0.01) the ammonia nitrogen (NH(3)-N) concentration in fermentation liquid compared to SBM. The short-chain fatty acids (SCFAs) contents were greater (P = 0.05) and acetate was lower (P < 0.01) in SBM than those in RSM and CSM, whereas propionate was greater (P < 0.01) in RSM than that in SBM, consequently reducing the acetate to propionate ratio (A/P) in RSM. Bacteroidetes, Firmicutes, and Proteobacteria were detected as the dominant phyla, and the relative abundances of Spirochaetae (P < 0.01) and Chlorobi (P < 0.05) declined in the CSM and RSM groups as compared to those in the SBM group. At the genus level, Prevotella_1 was the dominant genus; as compared to SBM, its relative abundance was greater (P < 0.01) in CSM and RSM. The abundances of Prevotellaceae_Ga6A1 and Christensenellaceae_R7 were lower (P < 0.05) in CSM, whereas Eubacterium_oxidoreducens_group, and Treponema_2 were lower (P < 0.01) in both CSM and RSM, and other genera were not different (P > 0.10). Although the bacterial community changed with different dietary protein sources, the disappearances of nutrients were not affected, suggesting that CSM and RSM could be used by rumen bacteria, as in case with SBM, and are suitable protein sources for ruminant diets.