Department of Animal Sciences, University of Florida, Gainesville 32611, USA.
J Dairy Sci. 2009 Dec;92(12):5988-99. doi: 10.3168/jds.2009-2343.
Environmental factors, especially temperature and light exposure, influence the health and productivity of dairy cows during lactation, possibly via similar physiological mechanisms. For example, heat stress is a critical component of decreased milk yield during summer. However, less is known about the effect of heat stress during the dry period. The objective of this study was to evaluate the effects of heat stress prepartum under a controlled photoperiod on lactation performance and hepatic metabolic gene expression of periparturient multiparous Holstein cows (n = 16). Cows were dried off approximately 46 d before expected calving date and assigned to treatment randomly after blocking by mature equivalent milk production and parity. Treatments consisted of either heat stress (HT) or cooling (CL) with fans and sprinklers, both under a photoperiod of 14L:10D. Rectal temperature was measured twice daily during the dry period. After calving, cows were housed in a freestall barn with cooling devices, and milk yield was recorded daily up to 210 d in milk. Blood samples were taken from dry off until +42 d relative to calving for metabolites and from -2 until +2 d relative to calving for hormone analysis. Daily dry matter intake was measured from -35 to +42 d relative to calving. Liver biopsies were collected at dry off, -20, +2, and +20 d relative to calving for cows on HT (n = 5) and CL (n = 4) to measure mRNA expression of suppressors of cytokine signaling-2 (SOCS-2), insulin-like growth factor binding protein-5 (IGFBP-5), a key transcription factor in lipid biosynthesis (SREBP-1c), and enzymes of lipid metabolism (FASN, ACACA, and ACADVL) by real-time quantitative PCR. Heat stress increased rectal temperatures (39.2 vs. 38.8 degrees C), plasma prolactin concentrations at -1 (171 vs. 79 ng/mL) and 0 d (210 vs. 115 ng/mL) relative to calving, and decreased dry matter intake at 0 and +14 d relative to calving and 3.5% fat-corrected milk postpartum (26.1 vs. 35.4 kg/d) compared with CL cows. Relative to CL cows, hepatic mRNA expression of SOCS-2 and IGFBP-5 was downregulated in HT cows. Expression of ACADVL was upregulated in CL cows at d +2 but downregulated at d +20 relative to HT cows. Concentrations of C16:0 and cis C18:1 were greater in the milk and liver of CL cows compared with HT cows, which reflects greater lipid mobilization. These results suggest that heat-stress abatement in the dry period improves subsequent lactation, possibly via suppression of plasma prolactin surge around calving, SOCS-2 expression, and regulation of hepatic lipid metabolism.
环境因素，尤其是温度和光照暴露，可能通过类似的生理机制影响泌乳期奶牛的健康和生产力。例如，热应激是夏季牛奶产量下降的一个关键因素。然而，对于干奶期热应激的影响知之甚少。本研究的目的是评估在受控光周期下产前热应激对围产期多产荷斯坦奶牛（n = 16）泌乳性能和肝脏代谢基因表达的影响。奶牛在预计产犊日期前约 46 天停奶，并在按成熟当量产奶量和胎次分组后随机分配处理。处理包括热应激（HT）或冷却（CL），均采用 14L：10D 的光周期。在干奶期每天测量两次直肠温度。产犊后，奶牛被安置在一个有冷却装置的自由站立牛舍中，每天记录产奶量，直到产奶 210 天。从干奶到产犊后 +42 天采集血液样本用于代谢物分析，从产犊前 -2 天到产犊后 +2 天采集血液样本用于激素分析。从干奶前 -35 天到产犊后 +42 天测量每日干物质摄入量。在产犊前 -20 天、产犊后 +2 天和 +20 天，对 HT（n = 5）和 CL（n = 4）组的奶牛进行肝脏活检，以测量抑制细胞因子信号转导-2（SOCS-2）、胰岛素样生长因子结合蛋白-5（IGFBP-5）、脂质生物合成关键转录因子（SREBP-1c）和脂质代谢酶（FASN、ACACA 和 ACADVL）的 mRNA 表达。热应激增加了直肠温度（39.2 与 38.8°C）、产犊前 -1 天（171 与 79ng/mL）和 0 天（210 与 115ng/mL）的血浆催乳素浓度，以及产犊后 0 天和 +14 天的干物质摄入量以及产后 3.5%脂肪校正奶（26.1 与 35.4kg/d）与 CL 奶牛相比。与 CL 奶牛相比，HT 奶牛的 SOCS-2 和 IGFBP-5 的肝脏 mRNA 表达下调。CL 奶牛在产犊后 +2 天的 ACADVL 表达上调，但在产犊后 +20 天的表达下调与 HT 奶牛相比。与 HT 奶牛相比，CL 奶牛的牛奶和肝脏中 C16:0 和 cis C18:1 的浓度更高，这反映了更大的脂质动员。这些结果表明，在干奶期减轻热应激可改善随后的泌乳性能，可能通过抑制产犊前后的血浆催乳素激增、SOCS-2 表达和调节肝脏脂质代谢来实现。
