Shading behaviour of sheep: preliminary studies of its relation to thermoregulation, feed and water intakes, and metabolic rates

Abstract

Two flocks of Merino ewes, containing 46 and 49 animals respectively, were observed for 6 days during summer while they grazed on irrigated pasture that was partly shaded.Approximately 20% of the animals stayed longer in the sun than the animals that used shade most. From the second flock, five animals of the shading (SH) group were compared in laboratory trials with five non-shading (non-SH) animals. During heat exposure to air temperatures rising from 20 to 50¦C over 3 h, non-SH sheep had significantly higher rectal temperatures and lower respiratory rates, suggesting that they were more thermolabile. SH sheep did not respond differently to non-SH sheep to being fed at 50¦C instead of 20¦C, although SH sheep ate significantly more food (24%) and drank significantly more water (33%) at both temperatures. In a further trial of individual feed and water intakes at 20¦C, differences in consumption were again recorded, but were not statistically significant. No significant difference in oxygen consumption between SH and non-SH animals was measured at 20¦C.The correlation between shading preferences and thermoregulation in these two flocks indicates that individual sheep may differ in their patterns of thermal adaptation when shading is optional. A possible relation between shading preference and food and water requirements suggests that shading patterns of sheep may also be associated with differences in nutritional adaptation.