Radcliff R P, McCormack B L, Keisler D H, Crooker B A, Lucy M C
Division of Animal Sciences, University of Missouri, Columbia 65211, USA.
J Dairy Sci. 2006 Feb;89(2):611-9. doi: 10.3168/jds.S0022-0302(06)72124-5.
Uncoupling of the growth hormone (GH) axis in early postpartum dairy cows is correlated with a decrease in liver GH receptor (GHR) 1A mRNA and a decrease in liver GH receptor protein. Postpartum recoupling of the GH axis is also correlated with GHR 1A mRNA and GHR protein. We hypothesized that dry matter intake (DMI) partially controls the increase in GHR 1A mRNA postpartum. Prepartum Holstein dairy cows (n = 11) were offered feed ad libitum. After calving, 6 cows were fed 70% of their expected DMI (feed restriction) for 14 d and 5 cows were fed ad libitum (control). Both groups were fed ad libitum after d 14. Liver was biopsied prepartum and on d 1, 7, 14, and 21 postpartum; blood was sampled throughout the experimental period. Rate of increase in postpartum milk production was less for feed-restricted cows. The GHR 1A mRNA decreased from prepartum to d 1 postpartum and subsequently increased. Rate of postpartum increase in GHR 1A mRNA was less in feed-restricted cows. Diminished GHR 1A persisted for at least 7 d after feed-restricted cows returned to ad libitum feeding. Liver insulin-like growth factor-I mRNA concentrations decreased from prepartum to d 1 as well, but were similar for feed restricted and control thereafter. We concluded that DMI partially controls GHR 1A mRNA expression in early postpartum dairy cows and that the decrease in GHR 1A in response to feed restriction persisted for at least 1 wk after ad libitum feeding was restored.
产后早期奶牛生长激素（GH）轴的解偶联与肝脏GH受体（GHR）1A mRNA的减少以及肝脏GH受体蛋白的减少相关。产后GH轴的重新偶联也与GHR 1A mRNA和GHR蛋白相关。我们假设干物质摄入量（DMI）部分控制产后GHR 1A mRNA的增加。产前给11头荷斯坦奶牛自由采食。产犊后，6头奶牛在14天内饲喂预期DMI的70%（限饲），5头奶牛自由采食（对照）。两组在第14天后均自由采食。在产前以及产后第1、7、14和21天对肝脏进行活检；在整个实验期间采集血液样本。限饲奶牛产后产奶量的增加速率较低。GHR 1A mRNA从产前到产后第1天下降，随后增加。限饲奶牛产后GHR 1A mRNA的增加速率较低。限饲奶牛恢复自由采食后，GHR 1A的减少持续至少7天。肝脏胰岛素样生长因子-I mRNA浓度也从产前到第1天下降，但此后限饲组和对照组相似。我们得出结论，DMI部分控制产后早期奶牛GHR 1A mRNA的表达，并且限饲后GHR 1A的减少在恢复自由采食后至少持续1周。
