生长期牦牛的氮代谢及补氮技术研究

本项目在放牧条件下 ,系统地研究了生长期耗牛对不同季节牧草蛋白质的采食、消化、利用 ,并得出了牦牛在维持状态下 ,不同生长速度下的蛋白质需要量 ,还研究了牦牛对非蛋白氮的消化与利用。本项目系统地研究了高寒草甸草场牧草营养的季节动态 ,实测了各时期牧草的生物量、保存率和营养成分变化。在上述2项研究的基础上 ,本项目比较了在全年之间、牧草与家畜之间蛋白质的供需平衡情况 ,所得到的冷季与暖季增重总数据与生产实践十分吻合 ,实测得到了冷季缺额数据。针对冷季蛋白质供应的缺额 ,筛选了几种直接补氮方法。发现在能量蛋白比适当的情况下 ,用糖蜜尿素舔砖自由采食 ,可使牦牛在约200天的冷季内 ,得到的可消化蛋白增加35 %左右 ,接近维持需要水平 ,从而大大地减少体重损失。在暖季用施肥方法间接补氮 ,也可以收到同样效果 ,但2种办法只能使氮的供应达到维持水平 ,使放牧牦牛在安全越冬的条件下 ,达到不减重或少减重

STUDY ON NITROGEN METABOLISM AND NITROGEN SUPPLEMENTARY TECHNIQUES IN GROWING YAKS

Under nature grazing condition,the intake,digestion and utilization of protein in grasses were systematicaly studied by growing yak during different phenological periods.Protein requirement for maintainance and grwoth were estimated,utilization of non protein N in yaks was studied too.Nutrient fluctuation in grasses on the alpine frigial meadow was systemly studied.The biomass,conservation rate and nutrient contents of grasses in different phenological periods were determined .In view of above-mentioned studies,the protein balance between different phenological periods,and between animals and pasture were dicussed,the conclusion for body weight gain during warm season,cold season and around the year was coincided with the production practice,the protein data of vacancy in cold season was gained.In connection with the vacancy,some nitrogen direct supplement methods were suggested.It was found,in the ration of energy and protein molasses-urea block could be given to yak in the limitation for 200-day during the cold season,in thus way digestible protein for yak could be increase by 35%,basically keeping the level for maintaining balance,and reduce the body weight loss remarkably. During warm season,indirect nitrogen supplement by nitrogen fertilizer also could get good effect.But these two ways only could keep animals nitrogen requirement at maintainance level,in the condition of making the grazing yaks aliving in winter safety to attain the goal at no body weight loss or less body weight loss.