In order to perfect the second generation of GI technical standard system, GI value of roughage and the milk yield were taken as parameters to set up the forecast model of the best supply level of concentrate in the diet of diary cows. 36 healthy Chinese Holstein cows in middle lactation stage were selected and randomly divided into 3 big groups （ with 3 groups in each big group, with 4 cows in each group ） according to the principles of with the same milk yield ,lactation period and similar fetal times. In the first big group ,yellow corn silage was used as roughage and the ratio of concentrate to roughage was 55：45,57.5：42.5 and 60：40 respectively, named as A1, A2 and A3. In the second big group, yellow corn silage and A neurolepidium chinense were used as roughage and the ratio of concentrate to roughage was 55：45,57.5：42.5 and 60：40 respectively, named as B1 ,B2 and B3. In the third big group,whole corn silage and A neurolepidium chinense were used as roughage and the ratio of concentrate to roughage was 55：45,57.5：42.5 and 60：40 respectively, named as CI ,C2 and C3. The effects of different roughage level （GI） and different concentrate supply level on the production performance of lactating dairy cows were studied. The results showed that lactoprotein, lactose and milk yield showed increasing trends and milk fat showed a decrease trend with the increasing of concentrate proportion. The ratio of concentrate to roughage had significant effects on milk yield （P〈0.05）and had some influences on milk composition （P〈0.05）. With the increase of roughage quality （GI）, milk fat and milk yield showed an increasing trend, and lactoprotein and lactose decreased, but its effects on milk fat, lactoprotein and lactose were not significant （P 〉0.05 ）, the effects on milk yield was significant （P〈0.05）.%为了完善二代GI技术标准体系，建立以粗饲料GI和产奶水平为参数的预测奶牛日粮科学精饲料给量模型。试验选取36头健康的泌乳中期中国荷斯坦奶牛，根据产奶量、泌乳天数、胎次相近的原则，随机分成3个大组，每个大组又分为3个小组，每个小组含4头奶牛。第1大组的粗饲料为黄贮，精、粗饲料比分别为55：45、57．5：42．5、60：40．标记为A1、A2、A3；第2大组为黄贮加羊草，精、粗饲料比分别为55：45、57．5：42．5、60：40，标记为B1、B2、B3；第3大组为全株玉米青贮加羊草，精、粗饲料比分别为55：45、57．5：42．5、60：40，标记为C1、C2、C3。研究不同粗饲料水平以及不同精料给量下，对泌乳奶牛生产性能的影响。结果表明，随着精料比例的增加，乳蛋白、乳糖和产奶量呈上升趋势．而乳脂呈下降趋势；精、粗饲料比对产奶量有显著影响（P〈0．05），对乳成分有一定的影响（P〉0．05）；随着粗饲料品质（GI）的提高，乳脂和产奶量呈上升趋势，乳蛋白和乳糖呈下降趋势，但是对乳脂、乳蛋白和乳糖的影响不显著（P〉0．05），对产奶量的影响显著（P〈0．05）。
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