Regulatory effects of diet energy and nitrogen balance on growth performance and rumen microecology of Angus calves aged 4 to 6 months

JIANG Qiufei; CHEN Liang; ZHANG Kun; FENG Yuan; AI Qi; LIU Ying; GU Yarong; TUO Zhengjun

doi:10.13557/j.cnki.issn1002-2813.2025.24.003

Abstract：The experiment aimed to investigate the effects of different energy and nitrogen levels of diet on the growth performance,serum biochemical indexes,rumen fermentation parameters,and microbial community of 4 to 6 month old Angus calves.A total of 30 healthy four month old Angus calves weighing(123.89±9.93)kg were randomly divided into three groups,with 10 replicates per group and one calf per replicate.The control group was fed a diet with a crude protein level of 14.50%and a comprehensive net energy of 5.62 MJ/kg,while the experimental group 1 was fed a diet with a crude protein level of 18.02%and a comprehensive net energy of 6.23 MJ/kg,the experimental group 2 was fed a diet with a crude protein level of 16.10%and a comprehensive net energy of 5.95 MJ/kg.The pre trial period was 10 days,and the formal trial period was 90 days.The results showed that the final weight in experimental group 1 was extremely higher than that of the control group(P<0.01),average daily gain was significantly higher than that of the other groups(P<0.05),and feed to gain ratio was significantly lower than that of the other groups(P<0.05).The body height in experimental group 2 was extremely higher than that of the other groups(P<0.01),and the cross height and chest circumference were significantly higher than those of the other groups(P<0.05).The serum total protein,blood glucose,and tumor necrosis factor-α levels in experimental groups 1 and 2 were significantly higher than those in the control group(P<0.05),and the glutathione peroxidase activity in experimental group 1 was significantly higher than that in the control group(P<0.05).Compared with the control group,the concentrations of rumen acetic acid,isobutyric acid,and total volatile fatty acids in experimental groups 1 and 2 were significantly increased(P<0.05),while the content of ammonia nitrogen was significantly decreased(P<0.05).The relative abundance of the genus Rikenellaceae RC9 gut group in experimental group 2 was significantly higher than that in the other groups(P<0.05),while the relative abundances of Patescibacteria and Proteobacteria in the control group were significantly higher than those in the other groups(P<0.05).The study shows that taking into account growth performance,serum biochemical indexes and rumen microecological balance,the recommended dietary crude protein level is 16.10%,and the comprehensive net energy is 5.95 MJ/kg for Angus calves aged 4 to 6 months.