Abstract :
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.
