Application of growth models to Boer x Mashona and Kalahari x Mashona goats under extensive semi-arid conditions.

The study aimed to estimate parameters from four different nonlinear growth models (Brady, Gompertz, Logistic, von Bertalanffy) and assess how growth differs by sex. A total of 40 goats (20 males and 20 females) for each cross; Boer x Mashona (BM) and Kalahari x Mashona (KM) were monitored from birth to one year of age. The goats were managed under extensive production with little or no supplements; singleton goat kids were used in this study. The model parameters of each growth model were compared for differences between the two sexes. The statistical effectiveness of fit was determined for each model using AIC, AICC, BIC, RMSE, and R² at the same time, the inflection weight (IW) and inflection age (IA) were determined. The main effect of sex was significant (P< 0.05) for all the parameters in all the models except parameter (k) in von Bertalanffy function in BM and KM goats. The asymptotic mature weight (A) predicted by the models ranged from 24.8 to 38.8 kg and 38.2 to 40.6 in BM, while it ranged from 24.8 to 38.3 and 35.1 to 37.3 in KM for female and male goats, respectively. The Gompertz model predicted that males and females are more or less similar in mature weight, with variation ranging between 0.03kg and 1kg for BM and KM, respectively. The IW ranged between 9.1 to 19.7 and 9.1 to14.1 kg, while the IA ranged from 4.9 to 57.5 and 12.2 to 51.5 days in BM and KM goats, respectively. The Brody and Logistic, and the Brody and Gompertz models were superior in modeling growth for BM and KM goats, respectively.