Selection response of US Holstein AI bulls for milk production in Chile and Argentina R.A. Verdugo a , A.A. Jara b , R.W. Everett c , N.R. Barrı ´a Pe ´rez b, * a Department of Animal Science, University of California Davis, Davis, CA 95616-8521, USA b Facultad de Ciencias Veterinarias y Pecuarias, Universidad de Chile, Casilla 2, Correo 15 La Granja, Santiago, Chile c Department of Animal Science, Cornell University, Ithaca, NY 14853-4801, USA Received 3 June 2003; received in revised form 23 October 2003; accepted 18 November 2003 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. D 2003 Elsevier B.V. All rights reserved. Keywords: Correlated response; Milk production; US Holstein sire; Chile; Argentina 1. Introduction Holstein breeding in Chile and Argentina has been initiated differently but has had a common develop- ment during the last few decades. The Argentinean Holstein herd started with Friesian cows brought from Holland in 1880 by President Julio A. Roca. They settled in three central provinces, but now they are spread over the region called ‘‘Pampa Hu ´meda’’ in the middle Argentina and in some minor areas in the north of the country (ACHA, 2002). In southern Chile the base-herd was introduced by the German colonists consisting of black and white and red and white Friesian cows. Since then the dairy population in both countries has been genetically modified by selection and by mating with other highly specialized 0301-6226/$ - see front matter D 2003 Elsevier B.V. All rights reserved. doi:10.1016/j.livprodsci.2003.11.001 Abbreviations: AI, artificial insemination; GE, genotype – environment interaction; HYM, herd-year-means; HYSD, herd- year-standard deviations; ME, mature equivalent; PTA, predicted transmitting ability. * Corresponding author. Tel.: +56-2-678-5572; fax: +56-2-678- 5611. E-mail address: vetbarri@uchile.cl (N.R. Barrı ´a Pe ´rez). www.elsevier.com/locate/livprodsci Livestock Production Science 88 (2004) 9 – 16