Department of Animal and Dairy Science, University of Georgia, Tifton 31793.
Department of Veterinary Pathology, Veterinary Diagnostic and Investigational Laboratory, University of Georgia, Tifton 31793.
J Dairy Sci. 2021 Apr;104(4):5021-5033. doi: 10.3168/jds.2020-19146. Epub 2021 Jan 28.
The objective of this study was to examine the effects of evaporative cooling and dietary supplemental Zn source on heat shock responses and mammary gland development of lactating dairy cows during summer. Seventy-two multiparous lactating Holstein cows were randomly assigned to 1 of 4 treatments in a 2 × 2 factorial arrangement. Cows were either cooled (CL) or not cooled (NC) and fed diets supplemented with 75 mg of Zn/kg of dry matter (DM) from Zn hydroxychloride (IOZ) or 35 mg of Zn/kg of DM from Zn hydroxychloride plus 40 mg of Zn/kg of DM from Zn-Met complex (ZMC). The 168-d trial included a 12-wk baseline phase when all cows were cooled and fed respective dietary treatments, and a subsequent 12-wk environmental challenge phase when NC cows were deprived of evaporative cooling. Plasma was collected from a subset of cows (n = 24) at 1, 3, 5, 12, 26, 41, 54, 68, 81 d of the environmental challenge to measure heat shock protein (HSP) 70 concentration. Mammary biopsies were collected from another subset of cows (n = 30) at enrollment (baseline samples) and at d 7 and 56 of the environmental challenge to analyze gene expression related to heat shock response, apoptosis and anti-oxidative enzymes, and to examine apoptosis and cell proliferation using immunohistochemistry. Supplemental Zn source did not affect milk yield but NC cows produced less milk than CL cows. Supplemental Zn source had no effect on mammary gene expression of HSP27, 70, and 90 or plasma concentrations of HSP70. The NC cows had greater mammary gene expression of HSP than CL cows. Circulating HSP70 of NC cows gradually increased and was higher at 81 d of environmental challenge compared with CL cows. Relative to IOZ, ZMC cows tended to have lower total mammary cell proliferation but greater mammary apoptosis. There was a tendency of greater TNFRSF1A mRNA expression for ZMC compared with IOZ cows, which may suggest upregulated extrinsic apoptosis. At d 7 of environmental challenge, NC cows had numerically higher mammary apoptosis than CL cows although not statistically significant. The NC cows tended to have greater mRNA expression of CAT and SOD3 regardless of time, and had greater mRNA expression of GPX1 at d 56 and FAS at d 7 of the environmental challenge than CL cows. Relative to CL cows, mammary cell proliferation rate was higher for NC cows at d 56 of the environmental challenge. In conclusion, dietary source of supplemental Zn has substantial effect on mammary cell turnover in lactating dairy cows, and prolonged exposure to heat stress increases mammary cell proliferation.
本研究旨在探讨蒸发冷却和日粮补充锌源对夏季泌乳奶牛热应激反应和乳腺发育的影响。将 72 头经产泌乳荷斯坦奶牛随机分为 4 种处理的 2×2 析因设计。奶牛要么冷却（CL）要么不冷却（NC），并分别饲喂补充 75 毫克/千克干物质（DM）锌的日粮来自氧化锌（IOZ）或补充 35 毫克/千克 DM 的锌和 40 毫克/千克 DM 的锌-蛋氨酸复合物（ZMC）。168 天的试验包括 12 周的基线期，所有奶牛均冷却并接受各自的日粮处理，随后是 12 周的环境挑战期，NC 奶牛被剥夺蒸发冷却。从一小部分奶牛（n=24）中采集血浆，在环境挑战的 1、3、5、12、26、41、54、68、81 天测量热休克蛋白（HSP）70 浓度。从另一部分奶牛（n=30）中采集乳腺活检，在入组时（基线样本）和环境挑战的第 7 和 56 天，分析与热应激反应、细胞凋亡和抗氧化酶相关的基因表达，并通过免疫组织化学检查细胞凋亡和细胞增殖。锌源补充对产奶量没有影响，但 NC 奶牛的产奶量低于 CL 奶牛。锌源补充对 HSP27、70 和 90 的乳腺基因表达或 HSP70 的血浆浓度没有影响。NC 奶牛的乳腺 HSP 基因表达高于 CL 奶牛。NC 奶牛的循环 HSP70 逐渐增加，在环境挑战的第 81 天高于 CL 奶牛。与 IOZ 相比，ZMC 奶牛的总乳腺细胞增殖倾向较低，但乳腺凋亡较多。与 IOZ 奶牛相比，ZMC 奶牛的 TNFRSF1A mRNA 表达有增加的趋势，这可能表明细胞外凋亡增加。在环境挑战的第 7 天，NC 奶牛的乳腺凋亡数高于 CL 奶牛，但无统计学意义。NC 奶牛无论时间如何，CAT 和 SOD3 的 mRNA 表达均有升高的趋势，GPX1 在环境挑战的第 56 天和 FAS 在第 7 天的 mRNA 表达均高于 CL 奶牛。与 CL 奶牛相比，在环境挑战的第 56 天，NC 奶牛的乳腺细胞增殖率较高。总之，日粮补充锌源对泌乳奶牛乳腺细胞的更新有显著影响，长期暴露于热应激会增加乳腺细胞增殖。
