Evaluation Of Growing Yaks’ Growth Potential On Qinghai Plateau By Warm Season Supplementation

To evaluate the growth potential of grazing yaks during warm season,the nutrient supply potential and carrying capacity of grazing pasture grass,associate effects of concentrate feed with native pastures grass were studied by general nutrient analysis method and in vitro gas production methods.And the effects of supplementary feeding concentrate on production performance,blood biochemical indexes and meat quality of growth period yak（one,two and three years old）were reaserched.The correlation of ruminal VFA and yak meat production,processing quality,eating quality was also studied.What’s more,the main factors influencing the growth of yak during warm season were analysed.The main research results were as follows:1.The highest edible dried grass production during warm season was found in autumn pasture,and the CP content of grass gradually decreased with growth,the change trend of NDS was similar with CP,but the change of NDF and ADF content were opposite.Under no supplementary feeding conditions,the optimum capacity of summer,antumn and winter pasture were 7.05,19.51 and 2.47SU·hm^-2.Supplementary feeding concentrate can improve the grazing capacity of natural grassland.2.The combination of concentrate and natural grass of warm season by50:50 was optimal.3.The average weight gain and average daily gain of one-year-old,two-years-old and three-years-old yak of treatment group was significantly（P<0.01）higher than control group.After 120d supplementary feeding,the weight of one-year-old yak of supplementary group was similar to two-years-old of control group,and yak fattening time can be shortening 1 year.During the early summer and mid-summer,nutrition and age were important factors significantly influencing growth speed of yak.However,nutrition was the only factor during last summer.4.There were many significant difference of blood biochemical indexe between treatment and control group yak,such as BUN connected with nitrogen use efficiency and P concerned with growth.Also,there were’t many significant difference,such as TG and TCh which have something to do with body fat metabolism of yak.5.Supplementary feeding concentrate can significantly reduce the acetic acid and propionic acid ratio,but can’t significantly influence PH,NH₃-N,middle and long chain fatty acid and VFA.6.Supplementary feeding concentrate can significant increase the dressing percentage of yak,and reduce the pH₂₄ of yak meat,but there was not signigicant influence on eating and processing quality of yak meat.And it can significant reduce the content of EPA of yak meat,but there was not signigicant influence on other fatty acid,conventional nutrition and 18 kinds of amino acids.7.VFA content of yak ruminal was closely related to slaughtering performance.In addition to the acetic acid and propionic acid ratio of VFA was closely related to the pH₂₄ value of the yak meat,VFA content of yak ruminal had no significant correlation with eating and processing quality.