Revista Brasileira de Zootecnia
On-line version ISSN 1806-9290
DURAES, Marcus Cordeiro et al. Genetic trend for milk and fat productions for Holstein cattle in Minas Gerais State. Rev. Bras. Zootec. [online]. 2001, vol.30, n.1, pp. 66-70. ISSN 1806-9290. http://dx.doi.org/10.1590/S1516-35982001000100011.
The objective of this work was to estimate the genetic trends for milk and fat yields of Holstein Dairy Cattle, in Minas Gerais State, Brazil. The statistical analyses were made by means of mixed models, using restricted maximum likelihood and animal model. The fixed effects studied were: herd-year-season at calving and linear and quadratic effect of age at calving besides the animal and residual random effects. The genetic trends were obtained by regression of the breeding value on the year of birth of cows. Records used in the analyses were 18,482 first lactations of cows born from 1986 to 1996. The genetic trends for milk and fat yield were 18.4 and 0.6 kg, respectively. The average of milk and fat yields were 5083 ± 50 to 6876 ± 51 kg, and from 172.6 ± 1.7 to 228.5 ± 1.7 kg, respectively. The breeding values estimated were negative in 1986 and 1987, and positive thereafter, with accentuate increase in the last years. This is an indication that milk farmers of Minas Gerais State have been taking strategies in order to increase the milk productions.
Keywords : animal model; genetic parameters; maximum likelihood.