Effects of granular feed with different crude protein levels on in vitro rumen fermentation of weaned calves

ZONG Yujie; CHENG Zhiqiang; LIU Wengboyang; LIU Li; ZHAO Jingwen; WU Rijin; LIN Miao

doi:10.13557/j.cnki.issn1002-2813.2025.05.001

Abstract：The aim of this experiment was to investigate the effects of different crude protein(CP)levels on in vitro rumen fermentation parameters and bacterial flora of weaned calves.In vitro rumen fermentation technique was used,and the crude protein levels were 16.0%,18.5%,21.0%and 23.5%granular feed as the substrate.The gas production,gas composition,fermentation parameters and rumen bacterial flora were determined by anaerobic culture for 48 h.The results showed that compared with CP level of 16.0%,the gas production at 24,36 and 48 h at CP level of 21.0%and 23.5%was significantly decreased(P<0.05),the unit hydrogen,methane and carbon dioxide production were significantly decreased(P<0.05),and the pH value and ammonia nitrogen(NH3-N)concentrations were significantly increased(P<0.05).The concentrations of microbial protein(MCP),isobutyric acid,and valeric acid at 23.5%CP level and the relative abundance of Proteobacteria were significantly increased(P<0.05).Compared with CP level of 16.0%,the relative abundances of Verrucococcus,Cyanobacteriota,Patescibacteria and Veillonella at CP level of 18.5%,21.0%and 23.5%were significantly decreased(P<0.05).Compared with the other three groups,the relative abundances of Ruminococcus,Eubacterium coprosterogenes and R-7 genera of Christensenaceae with CP level of 18.5%were significantly increased(P<0.05).The results show that increasing the dietary CP level of weaned calves can promote the synthesis of MCP,and lower CP level may promote rumen fiber degradation of weaned calves by increasing the relative abundance of fibrine-degrading bacteria such as Ruminococcus in the rumen,and the appropriate CP level of weaned calves is 21.0%considering the grain feed.