RESISTANCE TO COLD STRESS IN SHEEP SHORN BY COVER COMB OR STANDARD COMB

The cover comb has been developed in New Zealand as a means of increas ing residual fleece depth after shearing and so increasing the resista nce of shorn sheep to cold stress. The effects of shearing by cover co mb and standard comb were studied over 2 days pre-sheaving and 10 days post-shearing in eight pairs of non-pregnant, non-lactating 2-year-ol d ewes. Animals were housed and given a maintenance level of chaffed l ucerne hay. One member of each pair was shorn with a cover comb, the o ther with a standard comb. Each pair was exposed to 'cold plus wind' ( 7 degrees C ambient temperature, 7 km/h air movement) followed by 'col d plus wind plus rain' (10 degrees C ambient temperature, 7 km/h air m ovement, wetting at a rate equivalent to 25 mm/h rain from overhead sp rinklers) in a calorimetry chamber on days S - 3, S - 2, SO (day of sh earing), S2, S6 and SIG. Heat production immediately after sheaving (S O) teas proportionately 0.22 greater in ewes shorn by the standard com b under conditions of 'cold plus wind' and 0.38 greater under conditio ns of 'cold plus wind plus rain' than in their cover comb-shorn cohort s. Circulating concentrations of non-esterified acids were substantial ly elevated on the day of shearing and 2 days thereafter in ewes shorn by the standard comb, indicating increased rates of body fat mobiliza tion to support heat production in these ewes compared with those shor n by fire cover comb. This was reflected in it 1.4 kg weight loss il I the standard comb-shorn ewes compared with a 0.4 kg live-weight gain in the cover comb-shorn group over the 10 days of the experiment. It w as concluded that use of a cover comb will significantly reduced the r isk of death from hypothermia in sheep shorn during winter and spring, and should facilitate an increase in the productivity of animals by a llowing a greater proportion of food energy to be used for productive purposes.