低蛋白日粮补充过瘤胃氨基酸对肉牛生长性能、养分表观消化率、血清生化指标、氮代谢及肉品质的影响OA

This study aimed to investigate the effects of supplementing rumen-protected amino acids in low-protein diets on the growth per-formance,apparent nutrient digestibility,and nitrogen metabolism of beef cattle.Sixty beef cattle with similar body weight,age and good health status were selected and randomly divided into four groups with an equal number of animals in each group.The control group(Con)was fed with a basal diet at a low protein level,while the diet of the experimental groups were supplemented with 15 g of rumen-protected methionine per day(GroupⅠ),15 g of rumen-protected lysine per day(GroupⅡ),and 15 g each of rumen-protected methionine and ru-men-protected lysine per day(GroupⅢ).The pre-test period lasted for 7 days,and the formal test period was 80 days.Finally,indicators including growth performance,apparent nutrient digestibility,serum biochemical parameters,nitrogen metabolism indices,and amino acid contents in muscle were determined.The results showed that supplementing rumen-protected amino acids in low-protein diets significantly increased the average daily gain(ADG)of the beef cattle(P<0.05).GroupⅢhad the highest ADG,with an increase by 15％,compared with the control group(P<0.05);but there was no significant difference in feed intake among all the groups.In this experiment,the appar-ent digestibility of dry matter(DM),crude protein(CP),crude fat(CF),neutral detergent fiber(NDF),acid detergent fiber(ADF),and phosphorus(P)in the experimental groups was higher than that in the control group.Among them,the apparent digestibility of crude protein,neutral detergent fiber,acid detergent fiber,and phosphorus in Group Ⅲ were significantly higher than those in the control group(P<0.05).However,the apparent digestibility of calcium in all the experimental groups was lower than that in the control group,with no significant difference(P>0.05).There were no significant differences in serum biochemical indices of the beef cattle among all the groups(P>0.05).In terms of nitrogen metabolism,no significant differences were observed in all the indices among the groups(P>0.05).Addi-tionally,the amino acid contents in the muscle of the beef cattle showed no significant differences across all the groups(P>0.05).This stud-y provided a theoretical basis for rational application of low-protein diets in beef cattle breeding.