Genetic parameters of milk and fat yields of Holstein cows in the three first lactations

In this study 9,527 lactations of purebreed Holstein cows, calved between 1988 to 1997, from herds in the Minas Gerais State, were analysed. Two data sets were established: one with first lactations only and another with the first lactation until the third one. Milk and fat 305-day yields were analysed using a multivariate mixed model and restricted maximum likelihood procedure (REML). The milk and fat 305 days yields averages were respectively 5,870 +/- 1,662 kg and 199 +/- 55 kg for Set I and 5,521 +/- 1,523 kg and 187 +/- 50 kg for set II in the first lactation, and 6,421 +/- 1,789 kg and 215 +/- 58 kg for the second lactation, and 7,045 +/- 1,903 kg and 231 +/- 60 kg for the third lactation, respectively. Heritabilities estimated for milk and fat yields in set I (first lactation) were .28 +/- .04 and .20 +/- .03 and using the set II. were .16 +/- .09 e.9 +/- .9 for milk and fat yields in the first lactation,.17 +/- .11 and.20 +/- .11 for second one, and.16 +/- .10 and .10 +/- .16 in third lactation, respectively. Genetic correlations were high and ranged from .86 to 1.0.