ENVIRONMENTAL AND GENETIC INFLUENCES ON GROWTH-PERFORMANCE OF LAMBS IN DIFFERENT FATTENING SYSTEMS

Purebred Flemish Milksheep (M) and Suffolk (S) breed were double-recip rocally crossed to develop a highly fertile ewe genotype (SM male X MS female or F2, called Lovenaar),which was finally crossed with Texel s ires to improve carcass and slaughter characteristics of the final sla ughter lamb genotype: F3 or T male X F2 female. Growth of Texel male X (Milksheep male X Suffolk female) (T(MS))-lambs were studied for effi ciency of second reciprocal crossing, while postnatal growth performan ces during early postnatal life of Texel male X (F2 male X F2 female) (T(F2fix)) lambs were tested for preservation of the superior characte ristics of crossbreds when fixating the Lovenaar crossing scheme. Infl uence of birth weight (BW) on growth remained significant after weanin g during intensive stable fattening. While lambs of yearling ewes grew slower during the suckle period, during fattening these lambs had a h igher growth rate. Differences between lambs born single or as twins, triplets or quadruplets were not significant during fattening. The dec rease of superiority of single-suckling lambs during fattening occurre d only in non-extra-fed lambs on pasture, not in extra-fed lambs. In a ll three fattening schemes ram lambs realized a better growth than ewe lambs. Choice of fattening system had an important influence on growt h rate. In early-weaned, intensively fattened lambs a postweaning depr ession appeared at 18 kg BW. This could not be observed in lambs on pa sture, but they showed a reduction in growth from BW of 32 kg onwards. This decrease was observed earlier and more pronounced in non-extra-f ed lambs on pasture (28 kg). T(MS)-lambs seemed to be better suited fo r fattening at pasture, while F3-lambs realized best growth during sta ble fattening, but with a higher intake of commercial pellet feed. Ext ra-fed F3- and T(F2fix)-lambs on pasture realized comparable growth to purebred Texel lambs. There were no differences in growth rate betwee n F2- and F2fix-lambs, nor between F3- and T(F2fix)-lambs during fatte ning on pasture. According to the selected Texel sire, growth performa nce 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 u nder different fattening conditions.