Olsson K, Dahlborn K
Department of Animal Physiology, Swedish University of Agricultural Sciences, Uppsala.
Q J Exp Physiol. 1989 Sep;74(5):645-59. doi: 10.1113/expphysiol.1989.sp003317.
Fluid balance and thermoregulation were studied during an acute heat load (maximal daily temperature, 38 +/- 1 degrees C; night temperature 27 +/- 1 degrees C) in six goats during lactation and non-lactation. The goats had free access to water for 1 day, followed by 29.5 h of water deprivation and then water was returned. With water available the goats increased water intake and urinary and milk water losses, while plasma and milk osmolality decreased. Water deprivation caused plasma osmolality and vasopressin concentration to increase most in lactating goats. Milk osmolality rose to values similar to plasma osmolality. Plasma cortisol increased in lactating goats at the end of dehydration. Renal Na+ excretion increased during dehydration in lactating goats. Evaporative heat loss was larger in lactating goats when hydrated, but became less than in non-lactating goats during dehydration. Lactating goats exhibited higher respiratory frequency and rectal temperature than non-lactating goats. In conclusion, our results show that goats increase the water turnover during heat stress if allowed to drink ad libitum, but when they are deprived of water lactating goats reduce water loss in urine, milk and by evaporation, and rectal temperature reaches higher levels than in non-lactating animals. This saving of water could allow milk production to be maintained for a longer time during heat stress.
在六只处于泌乳期和非泌乳期的山羊身上，研究了急性热负荷（每日最高温度38±1℃；夜间温度27±1℃）期间的水平衡和体温调节。山羊可自由饮水1天，随后禁水29.5小时，然后恢复供水。在有水供应时，山羊的饮水量、尿液和乳汁中的水分流失增加，而血浆和乳汁渗透压降低。禁水导致泌乳期山羊的血浆渗透压和抗利尿激素浓度升高幅度最大。乳汁渗透压升至与血浆渗透压相似的值。脱水末期，泌乳期山羊的血浆皮质醇增加。泌乳期山羊在脱水期间肾脏的钠排泄增加。补水时，泌乳期山羊的蒸发散热较大，但在脱水期间其蒸发散热量小于非泌乳期山羊。泌乳期山羊的呼吸频率和直肠温度高于非泌乳期山羊。总之，我们的结果表明，如果允许自由饮水，山羊在热应激期间会增加水周转率，但当它们缺水时，泌乳期山羊会减少尿液、乳汁和蒸发造成的水分流失，并且直肠温度会比非泌乳动物达到更高水平。这种水分的节省可以使泌乳期山羊在热应激期间维持产奶时间更长。
