Abstract
Milk production has high economic importance in dairy cattle production systems, which justifies its inclusion in genetic breeding programs. The objective of this study was to evaluate the genetic and phenotypic trends of dairy traits in Gyr (167 lactations) and Guzerá (148 lactations) breeds in the State of Rio Grande do Norte (RN). Milk, fat and protein production obtained from monthly dairy controls were the traits evaluated. The expected differences in progeny (DEPs) for these traits were estimated using an animal model. From the means of phenotypic values and DEPs, we estimated the genetic and phenotypic trends in linear regressions as a function of the year of calving of the animal. Positive genetic and phenotypic trends were observed for Gyr (26.8 and 88.7 kg year-1) and Guzerá (8.44 and 37.68 kg year-1). Gyr breed presented positive genetic trends for fat (1.08 kg year-1) and protein (0.45 kg year-1) production and the Guzerá breed showed positive genetic trends for fat (0.36 kg year-1) and protein (0.25 kg year-1) production. The selection applied in the evaluated herds has produced satisfactory genetic and phenotypic progress for milk, fat and protein production.
Highlights
As production efficiency becomes fundamentally important to the production system, it is important to assess the genetic progress achieved throughout the selection process
Knowing the genetic progress of a population allows the breeder to analyze the results obtained with the breeding program (Malhado, Carneiro, Pereira, & Martins Filho, 2008), to know the distance between the selection objectives and the gains obtained over the years and to make the necessary adjustments
When choosing the traits to be included in a selection program, the heritability of the trait and its correlations must be taken into account, and its economic importance in relation to the general economic performance
Summary
As production efficiency becomes fundamentally important to the production system, it is important to assess the genetic progress achieved throughout the selection process. Milk production in general is the most economically important trait in dairy cattle breeding programs. This trait correlates with other important productive and functional traits in the. When choosing the traits to be included in a selection program, the heritability of the trait and its correlations must be taken into account, and its economic importance in relation to the general economic performance. The results depend on the environmental, genetic and value relationships between the traits involved. These relationships, if neglected, may result in losses in productivity and response to selection in each trait, and in the remuneration of these by industry (Lôbo, Madalena, & Penna, 2000; Madalena, 2000)
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