Effects of diets with different energy and protein levels on growth performance,nutrient apparent digestibility,and plasma indicators of fattening yaks
The experiment aimed to study the effects of diets with different energy and protein levels on the growth performance,nutrient apparent digestibility,and plasma indicators of fattening yaks.A total of 48 healthy yaks with similar body weight and condition,aged 2.5 years old,were selected and randomly divided into six groups with eight replicates in each group and one yak in each replicate,using a 3×2 factorial experimental design based on different energy(high,medium,low)and protein(high,low)levels.The pretreatment period was 15 days,and the formal experimental period was 60 days.The results showed that the high-energy group had significantly higher FBW and total weight gain than the low-energy group(P＜0.05).the high-protein group had significantly higher FBW and total weight gain than the low-protein group(P＜0.05).The interaction between energy and protein had a significant effect on total weight gain(P＜0.05).The high-energy group had the highest apparent digestibility of DM and CP,while the low-energy group had the lowest apparent digestibility,with significant differences between groups(P＜0.05).The high-protein group had significantly higher DM and CP apparent digestibility than the low-protein group(P＜0.05).The interaction between energy and protein had a significant effect on DM and CP apparent digestibility(P＜0.05).The high-energy group had significantly higher plasma TP and ALB levels than the low-energy group(P＜0.05),and the low-energy group had significantly higher plasma ALP activity than the medium-energy group(P＜0.05).The interaction between energy and protein had a significant effect on ALB and ALP(P＜0.05).Plasma IgA and IgG levels,T-AOC,and SOD activity increased with the increase in energy and protein levels(P＜0.0 5),while MDA content decreased(P＜0.05),and the interaction between energy and protein had a significant effect on T-AOC,SOD activity,and the content of IgA,IgG,and MDA(P＜0.05).The study indicates that a high-energy,high-protein diet can promote the growth of fattening yaks,improve plasma biochemical indicators,and enhance antioxidant and immune functions.It is recommended that the suitable dietary energy and protein levels for fattening yaks are 8.88 MJ/kg and 12.82％,respectively.
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