Veterinary Physiology, Vetsuisse Faculty, University of Bern, Bern, Switzerland.
J Dairy Sci. 2013 Aug;96(8):5008-17. doi: 10.3168/jds.2012-6245. Epub 2013 Jun 5.
During the transition period, the lipid metabolism of dairy cows is markedly affected by energy status. Fatty liver is one of the main health disorders after parturition. The aim of this study was to evaluate the effects of a negative energy balance (NEB) at 2 stages in lactation [NEB at the onset of lactation postpartum (p.p.) and a deliberately induced NEB by feed restriction near 100 d in milk] on liver triglyceride content and parameters of lipid metabolism in plasma and liver based on mRNA abundance of associated genes. Fifty multiparous dairy cows were studied from wk 3 antepartum to approximately wk 17 p.p. in 2 periods. According to their energy balance in period 1 (parturition to wk 12 p.p.), cows were allocated to a control (CON; n=25) or a restriction group (RES; 70% of energy requirements; n=25) for 3 wk in mid lactation starting at around 100 d in milk (period 2). Liver triglyceride (TG) content, plasma nonesterified fatty acids (NEFA), and β-hydroxybutyrate were highest in wk 1 p.p. and decreased thereafter. During period 2, feed restriction did not affect liver TG and β-hydroxybutyrate concentration, whereas NEFA concentration was increased in RES cows as compared with CON cows. Hepatic mRNA abundances of tumor necrosis factor α, ATP citrate lyase, mitochondrial glycerol-3-phosphate acyltransferase, and glycerol-3-phosphate dehydrogenase 2 were not altered by lactational and energy status during both experimental periods. The expression of fatty acid synthase was higher in period 2 compared with period 1, but did not differ between RES and CON groups. The mRNA abundance of acetyl-coenzyme A-carboxylase showed a tendency toward higher expression during period 2 compared with period 1. The solute carrier family 27 (fatty acid transporter), member 1 (SLC27A1) was upregulated in wk 1 p.p. and also during feed restriction in RES cows. In conclusion, the present study shows that a NEB has different effects on hepatic lipid metabolism and TG concentration in the liver of dairy cows at early and later lactation. Therefore, the homeorhetic adaptations during the periparturient period trigger excessive responses in metabolism, whereas during the homeostatic control of endocrine and metabolic systems after established lactation, as during the period of feed restriction in the present study, organs are well adapted to metabolic and environmental changes.
在过渡时期，奶牛的脂质代谢受到能量状态的显著影响。脂肪肝是产后主要的健康障碍之一。本研究旨在评估泌乳期两个阶段的负能量平衡（泌乳启动后即刻的负能量平衡和泌乳 100 天左右通过饲料限制故意诱导的负能量平衡）对肝脏甘油三酯含量和血浆及肝脏脂质代谢参数的影响，这些参数基于相关基因的 mRNA 丰度。50 头经产奶牛在产前 3 周至产后约 17 周（2 个时期）进行研究。根据它们在第 1 时期（分娩至产后 12 周）的能量平衡，奶牛被分配到对照组（CON；n=25）或限制组（RES；能量需求的 70%；n=25），在泌乳中期约 100 天开始（第 2 时期）进行 3 周的处理。产后第 1 周，肝脏甘油三酯（TG）含量、血浆非酯化脂肪酸（NEFA）和β-羟丁酸含量最高，此后逐渐下降。在第 2 时期，饲料限制并未影响 RES 奶牛的肝脏 TG 和β-羟丁酸浓度，而 NEFA 浓度则增加。在两个实验时期，肿瘤坏死因子α、柠檬酸裂解酶、甘油-3-磷酸酰基转移酶和甘油-3-磷酸脱氢酶 2 的肝 mRNA 丰度不受泌乳和能量状态的影响。脂肪酸合酶的表达在第 2 时期高于第 1 时期，但在 RES 和 CON 组之间没有差异。乙酰辅酶 A-羧化酶的 mRNA 丰度在第 2 时期与第 1 时期相比有升高的趋势。溶质载体家族 27（脂肪酸转运体），成员 1（SLC27A1）在产后第 1 周上调，在 RES 奶牛的饲料限制期间也上调。总之，本研究表明，奶牛在泌乳早期和晚期的负能量平衡对肝脏脂质代谢和 TG 浓度有不同的影响。因此，围产期的同源适应会在代谢中引发过度反应，而在产后建立泌乳后的内分泌和代谢系统的稳态控制期间，正如本研究中的饲料限制期间，器官能够很好地适应代谢和环境变化。
