Stress Hormone Responses of Sheep to Food and Water Deprivation at High and Low Ambient Temperatures
The effects of food and/or water deprivation at different ambient temperatures (7 or 35°C) on stress hormone release in sheep (n = 8), were studied to provide background data for research into the effects of road transport. Blood samples were taken from catheterized animals at the
start and, at 6h intervals, during 48h tests in an environmental chamber. Cortisol release was unaffected by temperature or deprivation state but was stimulated by introduction to the chamber. Prolactin secretion showed a similar tendency and levels of this hormone were generally higher in
the first test, whichever chamber was used. Heat exposure also had a prolonged stimulatory effect on prolactin release, especially in the first test. Growth hormone concentrations were rather variable but tended to be greatest when the animals were deprived of food. Measurements of plasma
osmolality indicated that sheep remained in water balance, even when water was withheld for 48h, unless they had access to food. The results suggest that under laboratory conditions, and over a wide thermal range, withholding food and water for 48h does not induce cortisol or prolactin release
in sheep. However, exposure to novel situations seems to have a stimulatory effect.