不同海拔下牦牛阶段化营养调控对生长发育及经济效益的影响OA

The long production cycle and low economic efficiency of yak production on the Qinghai-Ti-bet Plateau remain major challenges.This study aimed to shorten the finishing period and improve produc-tion efficiency by implementing nutritional regulation throughout the entire growth period of yaks under different altitude conditions,based on their growth and developmental characteristics.In the first stage,twelve 6-month-old weaned yak calves(47.33±5.28 kg)raised at high altitude(＞3 500 m)were subjected to a 186-day winter supplementary feeding trial.In the second stage,to address environmental changes and a more complex experimental design,the number of experimental animals was increased to 24(69.47±14.29 kg),which were then transferred to a mid-altitude region(3 100 m)and subjected to a 179-day sum-mer nutritional regulation trial with three dietary protein levels:low protein(LP),medium protein(MP),and high protein(HP).In the third stage,the 24 growing yaks(145.60±26.29 kg)were trans-ferred to a low-altitude area(2 100 m)for a 213-day winter indoor fattening trial with different dietary structures:concentrate+oat hay(COH),concentrate+oat silage TMR(COF),and concentrate+mixed oat/forage pea hay(COP).Growth performance at each stage and economic benefits were evaluated.At 24 months of age,four yaks from each group were randomly selected for slaughter evaluation.Results showed during the first stage,calves in the supplementary feeding group showed significantly greater weight gain than those in the grazing group(P＜0.01),with an average daily gain(ADG)of 247.31 g/d.In the second stage,the HP group exhibited significantly higher ADG(454.40 g/d)than the MP(420.99 g/d)and LP(413.93 g/d)groups(P＜0.05).In the third stage,the COP(469.48 g/d)group showed signifi-cantly higher weight gain than the COH(383.63 g/d)and COF(336.14 g/d)groups(P＜0.05).After slaughter,the dressing percentage of the COP group was 3.23％lower than that of the COF group and 1.37％lower than that of the COH group.The net meat percentage of the COP group was 0.79％higher than that of the COH group but 3.06％lower than that of the COF group.The stage-based nutritional strategy increased the average economic return per yak by 600～1 200 RMB during the production period,and after slaughter,fresh meat sales increased revenue by 2 700～3 500 RMB per animal.This study has shown that combining altitude and climatic gradient changes with precise nutritional regulation can signifi-cantly improve the growth rate of yaks and shorten the slaughter cycle.In particular,mixed oat and forage pea hay can reduce costs and increase efficiency during the growth-promoting stage of yaks,which is suit-able for popularization on the Qinghai-Xizang Plateau.