Covariance structure for carcass and body size traits with repeated measures in sheep from different genetic groups

Abstract

The purpose of this study was to evaluate the influence of environmental effects on body measurements, weight and carcass quality traits with structure of repeated measurements over time in sheep from different genetic groups. Collections were carried out from lamb in until 180 days of age, during the years 2012 and 2013, in 92 lambs from three genetic groups – 29from Santa Inês breed, 43 crossbred Dorper x Santa Inês, and 20 crossbred Dorper x Morada Nova – belonging to two flocks. Loin eye area, loin depth, subcutaneous fat thickness, height at withers, body length, thoracic depth, and body weight were measured. The effects of collection period, type of birth, sex, flock, genetic group, age of the animal at the time of measurement as a covariate in linear and quadratic effects, and interactions between the different effects were considered in the statistical model. Different structures were tested for modeling the residual (co) variance matrix. The structure that best fit the data was the Composed Symmetry. The interaction between genetic group and age as linear and quadratic effect was significantly important for modeling the traits studied. The environmental effects of the flock, type of birth, genetic group, and collection period influenced carcass traits, body measurements and weight. The genetic group originated from the Dorper x Morada Nova cross showed lower body size and better carcass traits.