The effects of breed, birthcoat and body weight on the cold resistance of newborn lambs

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Abstract
1. Twenty-two Scottish Blackface, 51 Welsh Mountain and 22 Tasmanian Merino lambs aged between 6 and 75 h were tested for resistance to body cooling in a climate chamber. Blackface lambs had long birthcoats, Merinos were short-coated. Welsh lambs were from two strains with long (L) and short (S) types of birthcoat. Some lambs were clipped before cold exposure.2. Clipping reduced cold resistance in Welsh (S) and (L) lambs by factors of 3 and 13 respectively.3. Undipped lambs showed significant breed differences, Welsh (L) and Blackfaces having the greatest cold resistance and Merinos the least. Long-coated lambs (Blackface and Welsh (L)) were on average six times more cold resistant than the average of Welsh (S) and Merino lambs; and Welsh (L) lambs were four times more resistant than the Welsh (S) type. Birth weight and age did not significantly influence cold resistance.4. In clipped lambs there was a significant positive linear regression between cold resistance and birth weight. Breed differences in cold resistance were still significant if no adjustment was made for the effect of breed differences in birth weight.5. Cold resistance was strongly influenced by breed differences in birthcoat morphology and probably by other physiological factors partly attributable to the different genetic backgrounds associated with birthcoat type. The breed differences in cold resistance were generally consistent with field data on mortality and body temperature regulation of lambs in severe weather, suggesting that climate chamber tests might be used to evaluate potential viability in the field.