Several research projects were undertaken to continue development of a genetic evaluation system for heat tolerance of U.S. Holsteins. Weather data from public weather stations were found to be as good as or better than data collected on farm. Also, weather data from test days captured less than half of the response to heat stress observed from daily data. A test-day model that accounts for heat stress was used to calculate national genetic evaluations for U.S. Holsteins. Heat-tolerant sires had lower evaluations for milk yield and dairy form, similar Type-Production Indexes, and higher evaluations for fertility and productive life compared with sires that were less heat tolerant. A genotype-by-environment interaction due to heat stress can be quantified on a national scale.

Ignacy Misztal, J. Bohmanova, M. Freitas, Shogo Tsuruta, H. D Norman, Thomas J Lawlor

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 01.12, 2006
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