Casper D P, Schingoethe D J
Dairy Science Department, South Dakota State University, Brookings 57007-0647.
J Dairy Sci. 1989 Dec;72(12):3327-35. doi: 10.3168/jds.S0022-0302(89)79494-7.
The depression of milk protein percentages for cows fed high fat diets in early lactation is a major problem facing the dairy industry. In order to describe more fully the mechanism involved, data involved 97 cows observations were summarized. Cows were fed diets containing corn-soybean meal or additional fat in the form of whole oilseeds as the main ingredients in the concentrate mix. Blood samples from the tail artery and subcutaneous abdominal vein were taken approximately 6- to 8-wk postpartum for amino acid analyses. Production of milk during the week of blood sampling was increased (36.9 and 39.6 kg/d) approximately 7.3% but milk protein percentages (2.91 and 2.79) were reduced for cows fed added fat. Intake of DM (21.1 and 21.4 kg/d) and BW (605 and 608 kg) were similar. Uptake of amino acids by the mammary gland, as measured by arteriovenous differences, was numerically lower for all essential amino acids and significantly reduced for histidine, isoleucine, leucine, phenylalanine, threonine, valine, and total essential amino acids for cows fed added fat. It is proposed that added fat inhibits somatotropin release from the anterior pituitary, thereby reducing mammary gland uptake of amino acids because of the role of somatotropin in aiding amino acid uptake. Administration of exogenous somatotropin with added fat diets may alleviate milk protein depression associated with such diets.
泌乳早期饲喂高脂肪日粮的奶牛乳蛋白率降低是乳制品行业面临的一个主要问题。为了更全面地描述其中涉及的机制，对97头奶牛的观测数据进行了总结。奶牛被饲喂以玉米 - 豆粕或全油籽形式的额外脂肪作为精料混合料主要成分的日粮。在产后约6至8周从尾动脉和腹壁皮下静脉采集血样进行氨基酸分析。采血周期间奶牛的产奶量增加（分别为36.9和39.6千克/天），约增加7.3%，但饲喂添加脂肪日粮的奶牛乳蛋白率（分别为2.91和2.79）降低。干物质摄入量（分别为21.1和21.4千克/天）和体重（分别为605和608千克）相似。通过动静脉差异测量，饲喂添加脂肪日粮的奶牛乳腺对所有必需氨基酸的氨基酸摄取量在数值上较低，组氨酸、异亮氨酸、亮氨酸、苯丙氨酸、苏氨酸、缬氨酸和总必需氨基酸的摄取量显著降低。有人提出，添加脂肪会抑制垂体前叶释放生长激素，从而由于生长激素在协助氨基酸摄取中的作用而减少乳腺对氨基酸的摄取。给添加脂肪日粮的奶牛施用外源性生长激素可能会减轻与此类日粮相关的乳蛋白降低情况。
