The influence of high ambient temperatures and plane of nutrition on wool growth rates of tropical sheep

Abstract

The wool production of two groups of tropical Merino sheep subjected to a simulated summer circadian temperature regimen, and fed either high or low quality diets, was compared with that of two other groups under similar nutritional conditions but held at prevailing winter ambient temperatures. The nutritional treatments were imposed for the duration of the experiment; the temperature treatments consisted of a. pre-experimental period of three weeks in which all groups were held at prevailing ambient temperatures b. heat adaptation period of one week in which the heat treatment groups were subjected to gradual increases in the circadian temperature regimen c. heat treatment period of three weeks in which the heat treatment groups were exposed to a circadian temperature regimen in which air temperatures were in excess of 38¦C for approximately 7 hours day-1d. post heat treatment period of three weeks in which all groups were held at prevailing ambient temperatures. Temperature treatment had no effect on feed intake or liveweight gain; however, intakes progressively decreased in groups on the low quality diet with a similar decrease in liveweight. Wool growth rates were unaffected by temperature treatment, but were significantly lower in animals on the low quality diet. The possible significance of these results to the wool production of tropical sheep is discussed.