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.

R. Finocchiaro, J. BCHM van Kaam, B. Portolano, Ignacy Misztal

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 02.03, 2006
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