Abstract
Indigenous Malawi goats were reared to five slaughter weight points (15, 20, 25, 30, and 35 kg). Half of these animals were raised on natural grass pastures while the other half were raised on natural grass pastures supplemented with maize bran. A normal pattern of tissue change was shown to occur, bone changes being relatively slow and muscle changes being relatively fast. Fat deposition paralleled muscle changes from 15 kg to 30 kg but above this body weight, fat deposition exceeded that of muscle. Supplementation with maize bran did not have any significant effect on the percentage of muscle or bone but produced significant (P < 0.05) differences in percentage carcass fat (9.82 and 8.04% for supplemented and unsupplemented, respectively). The influence of supplementation was more pronounced when total body fat (tissue plus internal cavity fats) was examined. This showed a greater increase in body fat when the goats were supplemented (1283.2 ± 231.8) compared to no supplementation (1259.6 ± 192.6). Muscle:fat ratio dropped from 13.48 ± 2.94 to 3.43 ± 0.59 as body weight changed from 15 kg to 35 kg. Actual amount of muscle and fat increased with an increase in body weight. Internal fat (r = 0.91) and muscle tissue (r = 0.96) appeared to be good indicators of live weight with the internal fat offering a more practical method on live weight prediction. Bone growth coefficients were much lower than unity (0.4015 and 0.5159 for unsupplemented and supplemented, respectively), indicating that bone was becoming a smaller proportion of carcasses as live weight increased. The growth coefficients of muscle tissue were much higher and closer to unity (0.8369 and 0.8763 for unsupplemented and supplemented, respectively). This supported the increase in lean:bone ratio (l.93:2.86) with an increase in live weight. Fat tissue growth coefficients were much greater than unity (2.6254 and 2.2860 for supplemented and unsupplemented, respectively), indicating that fat was increasing at a much faster rate and becoming a greater proportion of carcass as live weight increased. The differential growth rate of carcass fat exceeded that of muscle above live weights of 29 kg and 34 kg for the supplemented and unsupplemented, respectively.
