Genotype effects on energy and protein requirements in growing male goats

Abstract

<p>Goat genotype may alter the net energy and protein requirements for maintenance (<b>NE_m</b> and <b>NP_m</b>, respectively) and weight gain (<b>NE_g</b> and <b>NP_g</b>).This study was designed to investigate and quantify the effect of goat type on NE_m, NP_m, NE_g and NP_g, and quantify the net requirements for energy and protein for dairy, meat and indigenous growing male goats. For that, comparative slaughter studies were gathered and a meta-analytical approach was used. Two distinct databases were organized: one composed of 233 individual records from 11 studies of meat (<i>n</i> = 81), dairy (<i>n</i> = 97) and indigenous (<i>n</i> = 55) growing male goats weighing from 4.50 to 51.0 kg, to depict NE_m and NP_m; and another database composed of 239 individual records from nine studies of meat (<i>n</i> = 87), dairy (<i>n</i> = 97) and indigenous (<i>n</i> = 55) growing male goats weighing from 4.30 to 51.0 kg, to depict NE_g and NP_g. Our findings showed that NE_m of meat goats was 8.5% greater (336 ± 10.8 kJ/kg0.75 of empty BW; EBW) than dairy and indigenous goats (310 ± 8.20 kJ/kg0.75 EBW; <i>P</i> < 0.05). Whereas, NP_m was not affected by goat type (1.92 ± 0.239 g/kg EBW; <i>P</i> = 0.91). The NP_g was 185.1 ± 1.82 g/kg of EBW gain for goats weighing 5 kg BW and 192.5 ± 4.33 g/kg of EBW gain for goats weighing 45 kg BW, and thus did not change across goat type (<i>P</i> = 0.12). On the other hand, NE_g increased from 7.29 ± 0.191 to 11.9 ± 0.386 MJ/kg of EBW in male dairy goats, and from 7.32 ± 0.144 to 15.7 ± 0.537 MJ/kg of EBW in meat and indigenous growing male goats weighing between 5 and 45 kg BW. When body protein was used as a predictor in the allometric equation instead of EBW seeking to account for the degree of maturity, goat type differences disappeared; however, this predictor showed a high variation among individuals. In conclusion, energy and protein requirements for gain in distinct goat types reflect on body composition differences. Future research should focus on better understanding the maturity degree and its consequences in the energy requirement of growing male goats and better depict the goat type effect on it, as well as on the efficiency of utilization.</p>