Using body composition to determine weight at maturity of male and female Saanen goats

Abstract

The objective of this study is to provide approaches to determine mature weight of female and intact and castrated male Saanen goats using body composition data. Our database combined 7 comparative slaughter studies and comprised 244 individual records of body composition of intact male (n = 94), female (n = 71), and castrated male (n = 79) Saanen goats weighing from 4.6 to 51.0 kg BW. Nonlinear regressions were fitted to predict empty body water, fat (EBF), protein (EBP), and ash, expressed as amounts and percentages of the empty BW (EBW) and water-free EBW. Candidate equations were selected on the basis of preliminary graphical examination of the observed body composition of the database, and the best one to describe the data was selected on the basis of convergence achievement with coherent biological interpretation. The selected nonlinear functions were the allometric function (Y = beta(0) x EBW beta 1) to describe the EBF content and the exponential function (Y = beta(0) x e(-beta 1) x EBW) to describe EBP content in the water-free matter basis. None of the tested nonlinear functions were able to describe ash content, possibly because of its large variation. Mature weight was assumed to be the weight when net protein deposition (i.e., accretion minus degradation) tended to zero. The EBP (percentage of water-free EBW) plotted against the EBW using the exponential function enabled us to estimate the mature weight of intact and castrated males and females as 83.9, 33.6, and 26.4 kg EBW, respectively, indicating that the decrease of protein accretion of intact males approaches zero later than in females and castrated males during growth. Replacing these mature EBW estimates in the allometric function to describe the fat content in the EBW, we estimated that at maturity, castrated males and females had 21.6% and 22.4% EBF, whereas intact males had 36.8% EBF, which may not be biologically acceptable because it is too high. On the other hand, assuming that a goat matures at 22% EBF, one can backward estimate mature EBW of 42.6, 34.9, and 26.0 kg for intact and castrated males and females, respectively. This study indicated that fat percentage in the body may be used to describe maturity, as long as dietary challenges are not imposed on the animals. In addition, our results confirmed that female Saanen goats reach maturity at a lighter weight than males.