GROWTH CURVES THROUGH NON-LINEAR MODELS IN CREOLE LAMBS FROM THE MIXTECA REGION OF OAXACA, MEXICO

Background. Growth curves allow to predict the mature weight, the grow rate unto maturity, as well as the age and weight at inflexion point, to improve management on productive animals. Objective. To identify the best non-linear model (NLM), which best describe the growth curve of Creole sheep from the Mixteca region of Oaxaca, Mexico.  Material and methods. The live weights of 720 sheep (438 females and 239 males) between 1 and 60 months of age were used. The NLM evaluated were: Logistic, Gompertz, Michaelis-Menten, Weibull and Mechanist. Analyzes were performed with SAS JMP software. The criteria used to select the best model were the corrected Akaike information criterion (AICc), Bayesian (BIC) and coefficient of determination (R2). Results. For females, the Mechanist and Weibull models adjusted better de data (lowest AICc, BIC), but not being differences with the Michaelis-Menten and Gompertz. For males the lowest AICc, BIC and the highest R2 (0.84) values were for the Logistic, Gompertz and Mechanist models. Implications. The knowledge of the parameters of the growth curves of the creole sheep of the Mixteca region could be used for taking better decisions on the management of this type of sheep. Conclusion. According to the models, the inflection point of the growth curves was reached at a young age and a lower body weight in females than in males; therefore, different models should be used to study the growth kinetics between sexes.