Abstract
The correlated responses to selection of US AI dairy bulls from Chilean (45,447) and Argentinean (193,193) primiparous daughters lactating between 1992 and 1998 were estimated. Direct response obtained in the Northeast of the US (341,981) was also estimated for comparison with the Latin American results. Chile presented a higher production mean for 305-day milk yield (7162 kg) and fat (263 kg) than Argentina (6857 and 235 kg, respectively). Chile showed also a higher variability than Argentina. The responses were estimated using a regression coefficient of the adjusted production on the predicted transmitting abilities of the sires. The selection response for milk production was higher in Chile (0.566) than in Argentina (0.442) but lower than in the Northeast US (1.164). Similarly, the response for fat production in Chile (0.543) was almost half of the response in the US (1.101), and was very low in Argentina (0.095). Protein response could only be estimated in the US (1.209) and Chile (0.590). Chile and Argentina showed heterogeneity of responses by herd-year-mean (HYM) and herd-year-standard deviation (HYSD) levels of classification. The responses were lower than the response obtained in the US at similar levels. The differences in response were better explained by the levels of variation.
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