|
The objective of this study was to estimate energy requirements of indigenous goats weighing from 5 to 25 kg of body weight (BW). Goats were weaned at 79 ± 4.4 days after the beginning of experiment. Milk and solid diet intake were recorded daily. Total ration had 11.0 MJ/kg ME and 144 g/kg CP (DM basis). To determine energy maintenance requirements, 33 goats weighing 4.90 ± 0.302 kg of initial BW were used. Ten goats were slaughtered to estimate body energy and protein at the beginning of the experiment, then retained energy. The remaining goats were randomly assigned to two DM intake levels: ad libitum and restricted-fed (1.20X maintenance). Heat production was calculated as the difference between ME intake and retained energy (RE, kJ/kgEBW0.75). Net energy requirement for maintenance (NEm) was estimated as β0 of relationship between HP and MEI (Table 1, Eq.[1]). Metabolizable energy required for maintenance (MEm) was calculated iteratively, when HP = MEI. Efficiency of energy utilization for maintenance (km) was calculated as NEm/MEm. A linear regression of retained CP on CP intake (g CP/kg EBW0.75) was used to calculate net protein requirements for maintenance (NPm). The intercept of regression (Table 1, Eq.[2]). was assumed to be the endogenous and metabolic losses of N×6.25, which represented the NPm. Net energy and protein requirement for gain (NEg and NPg, respectively) were obtained using 26 goats fed ad libitum randomly slaughtered at 5.40 ± 0.484 kg BW (n = 10), 15.8 ± 0.655 kg BW (n = 10), and 26.3 ± 1.27 kg BW (n = 6). The first derivative of allometric equation (used to calculate energy and protein contents in the EBW; Table 1, Eq. [3] and [4]) with respect to EBW yielded estimates of the NEg and NPg. A Monte Carlo-based method was used to simulate variation of NEg and NPg. Estimated NEm was 344.1 ± 14.6 kJ/kgEBW0.75, resulting in 568.4 kJ/kgEBW0.75 MEm, thus km was 0.605. The NPm was 1.091 ± 0.435 g CP/kgEBW0.75·at NI = 0. The CP intake required for maintenance, at which retained CP = 0, was 3.87 g CP/kgEBW0.75. The growth phase, NEg ranged from 8.59 ± 0.555 to 8.75 ± 0.821 MJ/kg and NPg increased increased from 186.6 ± 5.25 to 230.8 ± 10.4 g CP/kg of empty weight gain in indigenous goats weighing from 5 to 25 kg BW. It is expected that indigenous goats are later maturing animals. That would explain the lack of significant increase in NEg as BW increased. We thank FAPESP for financial support (grant No. 2014/14939-0, 2014/14734-9, 2015/26000-5). |
|