Desempenho produtivo de vacas zebuínas em características de importância à produção de leite

Abstract

In dairy cattle, the economic performance of the production system is closely related to the productive performance of the herd. Thus, in the first chapter of this work, the objective was to verify the influence of body condition score (ECC) on productive traits of zebu cows. Data from 98 zebu cows of Gir and Guzerá breeds, belonging to the Agricultural Research Center of Rio Grande do Norte (EMPARN). For the statistical analysis, cows were previously grouped into classes of physiological stage, lactation period, somatic cell counting (CCS) and ECC, included in the model as fixed effects. Analyses were performed using the procedures available in SAS® computational package (SAS, 2009). ECC influenced (P <0.05) the milk fat content, with an increase of 0.25 percentage units in fat content for each increase of 0.5 in the ECC. The average milk constituents were higher in the first class (I) of days in milk (P <0.05). The second chapter aimed at determining the genetic and phenotypic trends of Gir and Guzerá herds belonging to that research center. For this, estimates of DEP (predicted transmitting ability) for milk production traits and components (fat and protein) obtained in the genetic evaluations of the National Breeding Program for the Improvement of Guzerá Dairy Cattle, using data of monthly milk records. Descriptive analyzes and regressions of different characteristics were performed using the statistical procedures available in the computational package SAS® (Statistical Analysis System). Positive genetic and phenotypic trends for milk production and constituents were observed in the Gir and Guzerá herds, except for the phenotypic trend for fat and protein in that of Guzerá breed.