The effects of wool length and nutrition on heat reactions of Merino sheep in the field

Abstract

Shorn sheep were more sensitive to changing ambient thermal conditions than unshorn sheep. The average 8.00 a.m. rectal temperature was lower, and the daytime rectal temperature equal to or greater than that of unshorn sheep during hot days. The average respiration rate of shorn sheep was up to twice that of unshorn sheep in the sun during the middle of the day. Wool tip temperature of unshorn sheep was greater than that of shorn sheep, apparently because of the greater absorptivity of the dark, dirt-impregnated rip. The average rectal temperature of sheep in poor body condition was more thermolabile than that of sheep in good body condition. During the early morning it was lower, and during hot sunny days it tended to increase to a higher value than that of the well conditioned sheep. The capacity of the sheep to dissipate heat was tested by imposing an added thermal burden through exercise. The average rectal temperature rise of the poor conditioned sheep was 2.9¦F, almost twice that of the well conditioned sheep, but heat dissipating mechanisms were adequate to eliminate much of the added heat within 40 minutes.