Desempenho produtivo e curva de lactação de animais mestiços holandês x gir na região agreste de Pernambuco

Abstract

The objective of this study was to evaluate the 305-day cumulative milk yield (MY305) and the lactation curve trajectory of cows from different genetic groups originating from the crossing of Holstein and Dairy Gyr breeds, daughters of proven and unproven sires. Milk yield records of 1,032 animals with a genetic composition of ½, ¾ and ⅞ Holstein x Gyr were used. The analyses to determine the effects of the genetic groups on the shape of the lactation curve were carried out in two steps: 1) pre-adjusting test-day milk yields for fixed effects in a linear model, and 2) using the adjusted yields in a nonlinear model on days in milk to compare the lactation curves of animals from different genetic groups, born to proven and unproven sires. The effects included in the linear model for pre-adjustment of test-day yields were the contemporary group and age class of cow at calving. The data were analyzed by the least squares method. The same model was used for MY305, which included the effects of genetic group of the animal and sire category (proven or unproven). MY305 was influenced by all effects (P<0.01). F1 daughters born to Gyr sires had lower mean MY305 and animals of the ⅞ HG genetic group exhibited higher mean MY305 compared to the other groups (P<0.001). The trajectory of the average lactation curves for all genetic groups was characterized by initial production, followed by an ascending phase until peak lactation and a descending phase thereafter. Only females of the ½ HG genetic group, daughters of Gyr sires, exhibited an atypical curve pattern. The different genetic groups had specific curves characterized by different trajectories and yields, with the observation of higher production levels in cows carrying a higher proportion of Holstein genes. The use of proven sires in dairy cattle crossings should increase genetic merit and consequently the productivity of the dairy herd evaluated.