Effect of ambient temperature and humidity on urine output in sheep

Urine output, respiratory rate, water intake, plasma and urine osmolalities, and PCV of 6 sheep exposed to 4 weeks of each of hot-humid, hot-dry, and cool-humid environments alternated with 3 weeks each of cool-dry control environments were determined. Compared with urine output during the control environment, urine output increased during hot-humid, hot-dry, and cool-humid exposure, but was 70% greater during the hot-humid environment than during hot-dry exposure. Water intake increased 37% to 45% during hot-dry exposure but decreased 35% during the first 2 weeks of cool-humid exposure. Urine osmolality decreased 38%, 22%, and 44% during hot-humid, hot-dry, and cool-humid exposure, respectively, whereas plasma osmolality values only increased 3% during hot-dry exposure. Respiratory rates increased on exposure to both hot environments, but decreased during cool-humid exposure. The PCV decreased 3% after 1 week of hot-humid exposure, 8% after 4 weeks of hot-dry exposure, and 5% after 4 weeks of cool-humid exposure. Urine output, and probably plasma volume, increased during these periods because evaporative heat loss was reduced due to the lack of adequate air convection and mobility. Heat loss through increased urine output was not significant (P less than 0.2). Enclosed sheep should be kept with short fleeces and should be maintained in conditions of low temperature and adequate convection if representative physiologic, biochemical, and pharmacologic assessments are desired.