Environmental and genetic influences on growth performance of lambs in different fattening systems

Abstract Purebred Flemish Milksheep (M) and Suffolk (S) breed were double-reciprocally crossed to develop a highly fertile ewe genotype (SM ♂ X MS ♀ or F2, called Lovenaar), which was finally crossed with Texel sires to improve carcass and slaughter characteristics of the final slaughter lamb genotype: F3 or T ♂ X F2♀. Growth of Texel ♂ X (Milksheep ♂ X Suffolk ♀(T(MS))-lambs were studied for efficiency of second reciprocal crossing, while postnatal growth performances during early postnatal life of Texel ♂ X (F2 ♂ X F2 ♀) (T(F2fix)) lambs were tested for preservation of the superior characteristics of crossbreds when fixating the Lovenaar crossing scheme. Influence of birth weight (BW) on growth remained significant after weaning during intensive stable fattening. While lambs of yearling ewes grew slower during the suckle period, during fattening these lambs had a higher growth rate. Differences between lambs born single or as twins, triplets or quadruplets were not significant during fattening. The decrease of superiority of single-suckling lambs during fattening occurred only in non-extra-fed lambs on pasture, not in extra-fed lambs. In all three fattening schemes ram lambs realized a better growth than ewe lambs. Choice of fattening system had an important influence on growth rate. In early-weaned, intensively fattened lambs a post-weaning depression appeared at 18 kg BW. This could not be observed in lambs on pasture, but they showed a reduction in growth from BW of 32 kg onwards. This decrease was observed earlier and more pronounced in non-extra-fed lambs on pasture (28 kg). T(MS)-lambs seemed to be better suited for fattening at pasture, while F3-lambs realized best growth during stable fattening, but with a higher intake of commercial pellet feed. Extra-fed F3- and T(F2fix)-lambs on pasture realized comparable growth to purebred Texel lambs. There were no differences in growth rate between F2- and F2fix-lambs, nor between F3- and T(F2fix)-lambs during fattening on pasture. According to the selected Texel sire, growth performance of F3-lambs was significantly different. F3-lambs born in spring, had a higher growth rate during fattening in comparison to lambs born in autumn. After correction for significant environmental influences, lambs of different genotypes had different genetic growth potentials under different fattening conditions.