Many applications of mixed models in genetic evaluation of dairy cattle assume constant residual and genetic variances across production environments. However, extensive research (Hill et al., 1983 ; Dodenhoff and Swalve, 1998 ; Ibáñez et al., 1999 ; Urioste et al., 2001) has found evidence of intra-herd heterogeneity of variances for milk traits. Some authors (e.g. Ibáñez et al., 1996) have grouped dairy herds in clusters characterized by similar production levels. Zwald et al. (2001) have posed climate, management and genetic level measures to describe dairy production systems in different countries. Recent research (Fikse et al., 2001 ; Kearney et al., 2001 ; Zwald and Weigel, 2001) suggests the existence of genotype by environment interactions in milk yield, both between and within countries. The objectives of this study are: (i) to identify and characterize different production systems for the Uruguayan Holsteins participating in Milk Recording Schemes, in terms of production level and management factors; (ii) to assess the presence of genetic by environment interactions by estimation of genetic (co)variances, heritabilities and genetic correlations between milk yield in the different production systems
Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume 2002. Session 1, , 1.7, 2002
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