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This study describes changes occurring in the live weight and body composition of male and female South African Black ostriches over a growing period of 285 days. Forty-five birds were given four diets with different protein (ca. 180 and ca. 120 g/kg feed) and energy (ca. 8.5 and ca. 13.5 MJ ME/kg feed) levels on a free choice basis, assuming that the birds would select feeds according to their protein and energy requirements and subsequently growing close to their genetic potential. Birds were weighed at approximately 10-day intervals and randomly selected birds (n = 9) were slaughtered at 1, 54, 120, 162 and 285 days of age respectively. Proximate chemical analyses were done on the complete empty carcasses and the components were expressed as a percentage of live weight at the different slaughter ages. An adapted form of the Gompertz growth curve (Wt = Wm*(exp(-exp(-B*(t-t*)))) (where Wt is body weight (kg) at time t (d), Wm is the mature weight (kg), B the rate of maturing (/d) and t* the age (d) at which growth rate is maximised), was fitted to the live weight data and the weights of each chemical component (calculated from percentage of total body weight). The growth parameters Wm, B and t* were calculated for each chemical component. The growth parameters Wm, B and t* were estimated as 119 kg, 0.009/d and 156 d respectively. Gompertz parameters estimated for the different chemical components were: BWam = 55.0, B = 0.014 and t* = 117 for moisture, BPm = 44.5, B = 0.015 and t* = 114 for protein, BLipm = 33.6, B = 0.013 and t* = 143 for lipid, and Bashm = 10.3, B = 0.016 and t* = 118 for ash. If it is assumed that ostriches in this study selected feed according to their protein and energy needs on each day of the growing period resulting in their growing close to their genetic potential, the results presented here would represent the potential growth rate of South African Black ostriches. Each chemical component was described by a Gompertz growth curve, and the rate of growth parameters illustrated that the tissues are allometrically related. Keywords: Development, feeding optimisation, Gompertz growth curve, growth, proportional changes

A description of body growth and composition of South African Black ostriches (Struthio camelus var. domesticus) under free-choice feeding conditions