Future Farming Systems Research Division, Department of Primary Industries, Ellinbank, Victoria 3821, Australia.
J Dairy Sci. 2011 Oct;94(10):5017-26. doi: 10.3168/jds.2011-4272.
This experiment measured variations in plasma concentrations of metabolic hormones and metabolites in cows undergoing extended lactations of up to 670 d at 2 planes of nutrition. Thirty-seven Holstein-Friesian cows that calved in late winter were selected for varying milk yield and then managed for a lactation of 670 d by delaying breeding until approximately 450 d in milk (DIM). Cows grazed fresh pasture supplemented with pasture silage or hay and crushed wheat or triticale grain. Dietary intake was reduced by approximately 1.8 kg (dry matter) grain/cow per day for 19 of the cows from 300 DIM until the end of lactation to assess the effect of restricted energy intake on the persistency of milk production. Samples of blood were collected monthly from each cow to measure plasma concentrations of selected hormones and metabolites. Dietary restriction beyond 300 DIM reduced yields of milk, protein, and fat, but did not alter the proportion of cows reaching the 670-d lactation target. Dietary restriction had no effect on cow BW or plasma concentrations of any hormones or metabolites. Overall, blood plasma concentrations of insulin-like growth factor-I, leptin, and glucose were elevated from 301 to 600 DIM compared with 0 to 300 DIM, whereas concentrations of growth hormone and nonesterified fatty acids were lower after 300 DIM. Plasma concentrations of insulin and prolactin were unaffected by stage of lactation, but prolactin concentrations increased during summer. These changes were consistent with a decrease in milk yield and an increase in the partitioning of nutrients to body tissue gain, primarily adipose tissue, throughout the later stages of the extended lactation. Cows that continued milking beyond 600 DIM had increased plasma concentrations of growth hormone and decreased concentrations of glucose and leptin compared with cows that milked <600 DIM. These differences, coupled with reduced body weight gain, indicated an increased priority for nutrient partitioning to milk production at the expense of body tissue gain throughout the extended lactation period in cows with greater lactation persistency.
本实验测量了在两种营养水平下，经历长达 670 天延长哺乳期的奶牛血浆代谢激素和代谢物浓度的变化。37 头荷斯坦-弗里森奶牛于冬季后期分娩，根据产奶量选择，然后通过在大约 450 天泌乳期延迟配种（DIM）来管理 670 天的泌乳期。奶牛放牧新鲜牧场，补充牧场青贮或干草以及粉碎的小麦或黑小麦谷物。19 头奶牛从 300DIM 到泌乳期末，每天大约减少 1.8 公斤（干物质）谷物/头，以评估限制能量摄入对产奶持久性的影响。每月从每头奶牛采集血液样本，以测量选定激素和代谢物的血浆浓度。300DIM 以后的日粮限制降低了牛奶、蛋白质和脂肪的产量，但没有改变达到 670 天泌乳目标的奶牛比例。日粮限制对奶牛 BW 或任何激素或代谢物的血浆浓度没有影响。总体而言，与 0 至 300DIM 相比，胰岛素样生长因子-I、瘦素和葡萄糖的血浆浓度从 301 至 600DIM 升高，而生长激素和非酯化脂肪酸的浓度在 300DIM 后降低。血浆胰岛素和催乳素浓度不受泌乳阶段的影响，但在夏季催乳素浓度增加。这些变化与牛奶产量的减少以及营养物质向身体组织（主要是脂肪组织）的分配增加一致，在延长泌乳期的后期阶段。与产奶量低于 600DIM 的奶牛相比，产奶量超过 600DIM 的奶牛的生长激素血浆浓度增加，葡萄糖和瘦素浓度降低。这些差异，加上体重增加减少，表明在延长泌乳期的奶牛中，为了维持牛奶产量而牺牲身体组织，对营养物质的分配优先级增加。
