Body composition and net energy requirements for Santa Ines lambs

A comparative slaughter trial was conducted on 24 non-castrated Santa Ines lambs (initial body weight 13.00 ± 0.56 kg) to determine their net energy requirements for growth and maintenance. Four animals were slaughtered at the start of the trial, as a reference group, in order to estimate the initial empty body weight (EBW) and body composition. The remaining animals were assigned to a randomized block design, with five replications per block, and four diets with increasing metabolizable energy contents (2.08, 2.28, 2.47 and 2.69 Mcal/kg DM). Non-linear regression analysis was used to describe heat production as a function of metabolizable energy intake; the net energy requirement for maintenance (kcal/EBW0.75/d) was estimated by extrapolation when MEI was set at zero. Regression equations of logarithms of body fat and body energy were then fitted onto the EBW logarithm. The derivatives of these equations allowed estimates of the fat content of the empty body weight gain (EBWG), and the net energy requirement for EBWG, respectively. The net energy requirement for maintenance obtained was 61.50 ± 4.56 kcal/EBW0.75/day. The energy and fat contents of the EBW of the animals increased from 1.91 Mcal/kg and 85.16 g/kg of EBW, respectively, to 2.78 Mcal/kg and 221.23 g/kg, as the BW increased from 15 to 30 kg. The net energy requirements for EBWG also increased, from 2.94 to 4.28 Mcal/EBWG, for body weights of 15 and 30 kg, respectively. There was no indication of a reduced value for the net energy requirement for maintenance of Santa Ines hair sheep, when compared with the values recommended by the major systems of nutrient requirements and feed evaluation.