Tendencias genéticas, ambientales y fenotípicas en un rebaño Brahman de registro

This study aimed to estimate the genetic, environmental, and phenotypic trends for 18-month weight (P540) in Brahman cattle. The research was conducted using 3,558 electronic records from the "La Cumaca" experimental station, part of the Faculty of Veterinary Sciences at the Central University of Venezuela. Genetic trends were estimated using three methods: a) by doubling the difference between the regression slopes estimated with the annual population means and the within-sire slope for the trait over years; b) using weighted regression analysis with the annual means derived from models adjusted with half-sibling or full-sibling groupings; and c) simple animal model. The models included the effects of sex, year and month of weight recording, and the effectsof the sire and dam, with variations involving the exclusion of ancestors to obtain trend estimates through differences in regression slopes. The genetic trend according to the first method was 1.2614 kg/year. Using half-sibling groups, the estimate was 3.0308 kg/year, while using full-sibling groups, the genetic change was 2.5332 kg/year. All three methods overestimated the annual genetic change, which was 0.829 kg/year using the animal model. The changes in reference to the population mean for the trait were less than 1%. Consequently, a revision of the selection procedure is suggested.