Protein metabolic profile of dairy cows fed corn and urea pasture

ABSTRACT The objective of this study was to evaluate the effects of total replacement of corn by soybean meal and urea on intake and apparent digestibility of dry matter, protein metabolic profile, and nitrogen balance of lactating crossbred cows grazing with intermittent stocking Mombasa grass (Panicum maximum). Twelve milking cows were distributed in a triple 4 x 4 latin design, with a mean initial body weight of 473,0+45,0kg, average lactation period of 95,0+42,2 days and milk production of initial mean of 14,1+1,9kg/day. Cows were primiparous and multiparous. The treatments consisted of four levels of substitution of soybean meal for corn and urea (0; 33; 66; 100% in dry matter - DM). The Mombasa grass showed an average content of crude protein and neutral detergent fiber of 19 and 59% in DM, respectively. The concentrations of urea and plasma urea nitrogen were altered by replacing soybean meal with corn and urea. Protein metabolic profile was changed with the replacement of soybean meal by corn and urea. The nitrogen balance was positive and has not changed with the replacements. For mixed-race cows producing an average of 12.5kg/day and kept in good-quality pastures, one can replace soybean meal totally with corn and urea.

摘要 本研究旨在评估以豆粕与尿素替代玉米，对间歇放牧蒙巴萨草（大黍，Panicum maximum）牧场的杂交泌乳母牛的干物质采食量与表观消化率、蛋白质代谢谱及氮平衡的影响。试验选用12头泌乳母牛，采用三重复4×4拉丁方设计，试验牛初始平均体重为473.0±45.0kg，平均泌乳天数为95.0±42.2天，初始平均产奶量为14.1±1.9kg/天，涵盖初产与经产母牛。试验设置4个以豆粕替代玉米与尿素的比例梯度（以干物质DM计分别为0、33、66、100%）。蒙巴萨草的干物质基础粗蛋白质与中性洗涤纤维平均含量分别为19%与59%。以豆粕替代玉米与尿素后，血液尿素及血浆尿素氮浓度发生改变；蛋白质代谢谱亦随替代比例变化发生改变。氮平衡呈正值，且不受替代比例变化的影响。对于日均产奶量约12.5kg、饲养于优质牧场的杂交母牛，可完全以玉米与尿素替代豆粕。