Body composition and net energy and protein requirements of Morada Nova lambs

A comparative slaughter trial was conducted with 48 Morada Nova lambs to assess the net energy and protein requirements for growth and maintenance. The animals were non-castrated and 2 months of age, with initial body weights averaging 12.05 +/- 1.81 kg (BW). Eight animals were slaughtered at the beginning of the trial as a reference group, in order to estimate initial empty body weight (EBW) and body composition. The remaining animals were assigned to a randomized block design with eight replications per block and five diets with increasing metabolizable energy contents (0.96, 1.28, 1.72, 2.18 and 2.62 Mcal/kg of dray matter (DM)). The heat production (HP) logarithm was regressed against metabolizable energy intake (MEI) and the net energy requirements for maintenance (kcal/kg EBW0.75/day) were estimated by extrapolation, when MEI was set at zero. The daily N excretion was estimated by extrapolating regression equations of N intake (g/kg BW0.75/day) as a function of retention (g/kg BW0.75/day) for zero intake. Regression equations for the logarithm of body fat, body energy and protein were fitted on the EBW logarithm. The derivatives of these equations allowed the estimation of the fat content of the empty body weight gain (EBWG) and the net energy requirement for EBWG. The net energy requirement for maintenance (NEm) obtained was 52.36 +/- 1.34 kcal/kg EBW0.75/day. The energy and fat contents of the EBW of the animals increased from 1.64 Mcal/kg and 79.38 g/kg, to 2.11 Mcal/kg and 123.73 g/kg of EBW, respectively, as the BW increased from 15 to 30 kg. The net energy requirements for EBWG increased from 2.15 to 2.78 Mcal/kg EBWG for body weights of 15 and 30 kg. Daily nitrogen excretion was 293.17 +/- 0.07 mg/kg BW0.75/day and the net protein requirement for maintenance (NPm) was 1.83 g/kg BW0.75/day. Protein content of the EBW of the animals increased from 161.67 to 175.28 g/kg of EBW when the BW of the animals increased from 15 to 30 kg. The amount of protein deposited during the gain increased from 177.84 to 192.93 g/kg of EBWG with the increase in body weight of the animals from 15 to 30 kg. The net energy and protein requirements for maintenance and gain in Morada Nova lambs is lower than values commonly recommended by the main evaluation systems for feed and nutritional requirements for lambs. (C) 2013 Elsevier B.V. All rights reserved.