Genetic evaluation of Guzerá cows using test day milk and fat yield

Abstract

Data from 467 lactations of 5.604 controls of bovine of the Guzerá cows, controlled between 1987 and 2004 were used with the objectives to estimate the genetic parameters and to predict the genetic values for the production of milk (PLDC) and fat (PGDC) and to compare it with the classification of the animals, for estimates obtained by ordinary test-day model. PLDC and PGDC were analyzed through an animal model, considering the first four milk yield (repeatibility model). The statistical models to analyze PLDC and PGDC included the addictive genetic direct effects and of permanent of ambient, like random, the fixed effect of contemporary group, formed by the year and the month of control, and the age of the cow at delivery as co-variable, linear and quadratic regression. In a general way, the estimaded herdabilidades were higher in the beginning and at the end of the lactation, indicating
possibility to the selection. The correlation order among the genetic values for production of total milk and production of total fat and PLDC and PGDC were greater in the beginning and half of the lactation that the one at the end. The selection for PLDC and PGDC in the beginning and end of the lactation it can be indicated as selection criterion, in substitution to the total production.