Farm animals respond to cold by restricting heat loss and increasing heat production. The overall effectiveness of this thermoregulation, which may determine survival, can be assessed from an animal's resistance to cooling under a standard cold exposure. Cattle are subjected to severe cold in some countries, e.g. Canada, but sheep are the farm animals most often exposed to cold both as lambs and as adults.
Cold resistance has been measured in shorn adult sheep and newborn lambs. Significant breed differences, possibly related to previous genetic adaptation, were found. There was also significant additive within-breed genetic variance for cold resistance (h^ = 30$) in both adult sheep and lambs. Different forms of physiological adaptation to cold, including acclimation (which conferred increased cold resistance) were demonstrated - most clearly in adults.
Genetic selection for cold resistance in newborn Scottish Blackface lambs produced a significant response in the upwards direction only. It was concluded that neonatal viability might be improved by genetic selection for cold resistance.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume XI. Genetics of reproduction, lactation, growth, adaptation, disease, and parasite resistance., , 462–473, 1986
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