A comparison of growth models for cross- and purebred lambs in precision livestock farming systems

Abstract

Implementation of precision livestock farming requires extensive information to be gathered on the production cycle of slaughter lambs. Constructing accurate growth models for crossbred sheep from the South African flock would provide valuable information towards this goal. Two dam lines, Dohne Merino and Merino, were mated to rams of their own breeds and to three sire lines, namely Dorper, Dormer and Ile de France. Four ram and four ewe lambs from each group were grown out until maturity at one year of age and weighed weekly. The age–weight data thus gathered were fitted to four growth models (Brody, Gompertz, Logistic, and von Bertalanffy) and the accuracy of fit was determined. All four models were deemed to provide a good fit for the data (R² >0.86). Comparison of predicted and observed weights showed that the Gompertz model was the best suited to predicting lifetime growth and therefore it was deemed the best model for this purpose. Crossbred animals generally achieved higher mature weights relative to the pure lines, although Dorper cross ewes were an exception. Rams also gained more benefit from heterosis for mature weights than ewes.