CRC for Innovative Dairy Products, Department of Zoology, University of Melbourne, VIC 3010, Australia.
J Dairy Sci. 2010 Dec;93(12):5913-20. doi: 10.3168/jds.2010-3609.
An experiment was conducted to measure the effect of diet on circulating concentrations of metabolic hormones and metabolites in cows undergoing extended lactations. Two groups of 6 Holstein-Friesian cows managed for lactations of 670 d were used in the experiment. One group was fully fed on a total mixed ration (TMR), whereas the other group grazed fresh pasture supplemented with grain (P+G). On 7 occasions between 332 and 612 d in milk, concentrations of metabolic hormones and glucose were measured in the blood plasma of each cow. Cows fed TMR gained more weight and body condition than P+G cows, but did not produce more milk during the study period. Only 3 of the TMR cows continued to lactate until 612 d in milk compared with all 6 of the P+G cows. Blood plasma from cows fed TMR had higher concentrations of glucose, insulin, glucagon, insulin-like growth factor 1, and leptin, but lower concentrations of growth hormone, than that from P+G cows. These changes were consistent with the preferential deposition of energy into adipose tissue at the expense of milk production and presumably were induced by a diet that provided precursors for gluconeogenesis that were in excess of the requirements for maintenance and prevailing milk production. The mechanism responsible for some TMR cows putting on excess weight and reducing or ceasing milk production is uncertain, but this observation has important implications for the nutritional management of cows in extended lactation programs.
进行了一项实验，以测量在延长哺乳期的奶牛中，饮食对循环代谢激素和代谢物浓度的影响。实验使用了两组 6 头荷斯坦-弗里森奶牛，分别管理 670 天的哺乳期。一组完全喂食全混合日粮（TMR），而另一组则放牧新鲜牧场，并补充谷物（P+G）。在产奶 332 至 612 天之间的 7 个时间点，测量了每头奶牛的血浆代谢激素和葡萄糖浓度。与 P+G 奶牛相比，TMR 组奶牛增重和体况更好，但在研究期间产奶量没有增加。只有 3 头 TMR 奶牛继续泌乳至 612 天，而所有 6 头 P+G 奶牛都继续泌乳。与 P+G 奶牛相比，TMR 组奶牛的血浆葡萄糖、胰岛素、胰高血糖素、胰岛素样生长因子 1 和瘦素浓度更高，而生长激素浓度更低。这些变化与优先将能量沉积到脂肪组织中以牺牲产奶为代价的情况一致，并且可能是由提供超过维持和当前产奶所需的用于糖异生的前体的饮食引起的。导致一些 TMR 奶牛增加体重和减少或停止产奶的机制尚不确定，但这一观察结果对延长哺乳期奶牛的营养管理具有重要意义。
