Milk and fat-plus-protein production and temperature-humidity index data were joined, resulting in 59 661 test-day records from 6624 lactations of 4428 lactating ewes in 17 flocks. Valle del Belice sheep, although originating from a hot environment, are affected by heat stress starting at a temperature-humidity index of 23 and this results in a decrease of production yields; daily milk and fat-plus-protein yield decreased by 62.2 g (-3.9%) and -8.6 g (-4.4%), respectively, per unit increase of the temperature-humidity index above 23. The genetic correlations between both production traits and heat tolerance additive genetic effects were around -0.80. These results imply that genetics for yield traits are antagonistic with heat tolerance and, therefore, single-trait selection for yields will result, in the long term, in animals with lower heat tolerance.
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 02.03, 2006
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