Clinic of Obstetrics & Reproduction, Veterinary Faculty, University of Thessaly, Karditsa, Greece.
Clinic of Obstetrics & Reproduction, Veterinary Faculty, University of Thessaly, Karditsa, Greece; Laboratory of Reproduction, Department of Animal Science, University of Thessaly, Greece.
Theriogenology. 2021 Dec;176:82-93. doi: 10.1016/j.theriogenology.2021.09.028. Epub 2021 Sep 28.
It is known that heat stress decreases dry matter intake in cattle with impacts on milk production and fertility. Ghrelin is an orexigenic hormone with suppressive effects on reproduction. In this study, we investigated the effects of heat stress and gestational status on ghrelin secretion and its possible associations with DMI in Holstein cattle. The study was conducted in a dairy farm without any artificial cooling measures. The animals were fed a total mixed ration twice daily; each morning the leftovers were removed and weighted. Lactating cows and heifers were used during the winter and the summer; in each season 8 groups were formed as following: non-pregnant cows (n = 10) and non-pregnant heifers (n = 10) and pregnant cows (3 groups, each n = 8) and heifers (3 groups, each n = 10), being at the 1st (days 65-90), the 2nd (days 114-144) and the 3rd (dry cows, days 198-220; heifers, days 192-230) trimester of gestation. In each season the blood samples were collected from all groups on the same day, 1 h prior to morning feeding. In the winter, the Temperature Humidity Index (THI) was 58 in the winter and 73 in the summer. Normal and acidified sera were stored at -20 °C and analyzed for cortisol, total and acylated ghrelin concentrations, respectively. T-Test and Welch-Satterthwaite were performed for continuous data comparison, while two-way ANOVA to test for differences between gestation and season. Feed refusals were higher (p < 0.01) during the summer compared to the winter. In cows, total ghrelin levels differed between gestation stages in winter and summer(p < 0.04), while acylated ghrelin levels differed by gestation stage in winter (p < 0.001) but not in summer. There was an effect of season by the gestational stage in the pattern of acylated (p < 0.001) but not of total ghrelin. In heifers, the pattern of total and acylated ghrelin secretion was not affected by season or gestation stage (p > 0.05). Both in cows and heifers, acylated ghrelin levels were lower in summer compared to winter, (p < 0.002). During the summer months the low ghrelin levels might explain the reduced feed consumption of heat stressed animals. We infer that the lactation-induced altered metabolic status of the animals governed the different ghrelin levels at various gestational stages in cows and heifers.
众所周知，热应激会降低奶牛的干物质采食量，从而影响产奶量和繁殖性能。Ghrelin 是一种食欲刺激激素，对繁殖有抑制作用。在这项研究中，我们调查了热应激和妊娠状态对 ghrelin 分泌的影响，以及其与荷斯坦奶牛干物质采食量的可能关联。该研究在一个没有任何人工冷却措施的奶牛场进行。动物每天两次喂食全混合日粮；每天早上都会取出并称重剩余的饲料。在冬季和夏季使用泌乳奶牛和小母牛；在每个季节，形成以下 8 组：未怀孕的奶牛（n=10）和未怀孕的小母牛（n=10）以及怀孕的奶牛（3 组，每组 n=8）和小母牛（3 组，每组 n=10），处于妊娠的第 1 期（第 65-90 天）、第 2 期（第 114-144 天）和第 3 期（干奶牛，第 198-220 天；小母牛，第 192-230 天）。在每个季节，所有组都在同一天、早上喂食前 1 小时采集血液样本。在冬季，温度湿度指数（THI）为 58，夏季为 73。正常和酸化的血清在-20°C 下储存，并分别分析皮质醇、总和酰化 ghrelin 浓度。连续数据的比较采用 T 检验和 Welch-Satterthwaite，而两因素方差分析用于测试妊娠和季节之间的差异。与冬季相比，夏季的饲料拒食率更高（p<0.01）。在奶牛中，总 ghrelin 水平在冬季和夏季的妊娠阶段有所不同（p<0.04），而酰化 ghrelin 水平在冬季因妊娠阶段而异（p<0.001），但在夏季则没有。在酰化 ghrelin 模式中，季节与妊娠阶段存在相互作用（p<0.001），但在总 ghrelin 模式中则没有。在小母牛中，总 ghrelin 和酰化 ghrelin 的分泌模式不受季节或妊娠阶段的影响（p>0.05）。在奶牛和小母牛中，夏季酰化 ghrelin 水平均低于冬季（p<0.002）。在夏季，ghrelin 水平较低可能解释了热应激动物采食量减少的原因。我们推断，动物的哺乳期引起的代谢状态改变控制了奶牛和小母牛在不同妊娠阶段的不同 ghrelin 水平。
