Kay J K, Phyn C V C, Roche J R, Kolver E S
DairyNZ Ltd., Private Bag 3221, Hamilton, 3240, New Zealand.
J Dairy Sci. 2009 Aug;92(8):3704-13. doi: 10.3168/jds.2008-1976.
Fifty-six genetically divergent New Zealand and North American Holstein-Friesian (HF) cows grazed pasture, and were offered 0, 3, or 6 kg of concentrate DM/cow per day for an extended lactation (605 +/- 8.3 d in milk; mean +/- standard error of the mean). Weekly blood samples collected from individual cows from wk 1 to 10 postpartum (early lactation), and from wk 47 to 63 postpartum (extended lactation) were analyzed for nonesterified fatty acids (NEFA), glucose, insulin, leptin, growth hormone (GH), insulin-like growth factor-I (IGF-I), calcium, and urea. During early lactation, NEFA and GH concentrations were greater and IGF-I concentrations were less, and increased at a slower rate in North American HF. During this 10-wk period, there were no strain effects on plasma glucose, leptin, insulin, or calcium. During the extended lactation period, North American HF had greater NEFA and GH concentrations; there were strain x diet interactions for insulin and leptin, and a tendency for a strain x diet interaction for glucose. These interactions were primarily due to greater plasma insulin, leptin, and glucose concentrations in the New Zealand HF fed 6 kg of concentrate DM/cow per day, a result of excessive body condition in this treatment. In this period, there was no strain effect on plasma IGF-I, calcium, or urea concentration. During early lactation, there was a linear increase in glucose and IGF-I, and a linear decrease in GH and urea with increasing concentrate in the diet. However, plasma calcium, NEFA, insulin, and leptin remained unchanged. During the extended lactation period, there was an effect of feed supplementation on GH and urea, which decreased linearly with increasing concentrate in the diet. There was, however, no supplementation effect on NEFA, calcium, or IGF-I. These data indicate potential strain differences in recoupling of the somatotropic axis, insulin resistance, and energy partitioning, and may help explain the physiology behind the previously reported greater milk production and body condition score loss in North American HF. The results have implications for breeding and diet management during an extended lactation.
56头基因存在差异的新西兰和北美荷斯坦-弗里生（HF）奶牛在牧场放牧，并在延长的泌乳期（平均产奶天数为605±8.3天；均值±均值标准误）内，每头奶牛每天分别给予0、3或6千克干物质精饲料。从产后第1周（早期泌乳）至第10周，以及产后第47周（延长泌乳）至第63周，每周采集个体奶牛的血样，分析其中的非酯化脂肪酸（NEFA）、葡萄糖、胰岛素、瘦素、生长激素（GH）、胰岛素样生长因子-I（IGF-I）、钙和尿素。在早期泌乳期间，北美HF奶牛的NEFA和GH浓度更高，IGF-I浓度更低，且增长速度较慢。在这10周期间，血浆葡萄糖、瘦素、胰岛素或钙没有品系效应。在延长泌乳期，北美HF奶牛的NEFA和GH浓度更高；胰岛素和瘦素存在品系×日粮交互作用，葡萄糖有品系×日粮交互作用的趋势。这些交互作用主要是由于每天每头奶牛饲喂6千克干物质精饲料的新西兰HF奶牛血浆胰岛素、瘦素和葡萄糖浓度更高，这是该处理组体况过肥的结果。在此期间，血浆IGF-I、钙或尿素浓度没有品系效应。在早期泌乳期间，随着日粮中精饲料增加，葡萄糖和IGF-I呈线性增加，GH和尿素呈线性下降。然而，血浆钙、NEFA、胰岛素和瘦素保持不变。在延长泌乳期，补充饲料对GH和尿素有影响，随着日粮中精饲料增加呈线性下降。然而，对NEFA、钙或IGF-I没有补充效应。这些数据表明在生长激素轴再耦合、胰岛素抵抗和能量分配方面可能存在品系差异，并且可能有助于解释之前报道的北美HF奶牛产奶量更高和体况评分损失背后的生理机制。这些结果对延长泌乳期的育种和日粮管理具有启示意义。
