Consequences of prolificacy on lambs rearing and on meat production

Abstract

Increasing litter size induces a reduction in birth weight of new born lambs. This reduction, close to 20 % for « classical » breeds, is limited to 15 % for the prolific ones. Body composition of lambs at birth varies with their weight ; their protein and fat contents decreasing with birth weight. The small sized lambs have more difficulty in adapting to the external environment and their neonatal mortality is much higher than that of heavy lambs. During the suckling period (6 to 8 weeks), daily milk consumption and growth rate of multiples are lower those of singles when expressed in absolute values (g/d) but identical on a relative basis (g/kg body weight/d). A one kg difference on birth weight induces a 2.4 kg body weight variation at 6-7 weeks of age. This discrepancy may increase after weaning when lambs are kept in an unfavorable environment (pasture) or remain constant when conditions are good (indoors). From 10- 12 kg live weight onwards, body composition of lambs, and particularly their body fat content, varies with birth size : the smaller the size at birth, the higher the animals fat content at a certain weight ; this is a consequence of the reduction in skeleton growth potential due to in utero under nutrition. Production of carcasses to a constant fatscore necessitates a reduction of the slaughter weight of multiple lambs, one less kg at birth reduces carcass weight by 0.6 to 1 kg.