ENVIRONMENTAL AND MATERNAL EFFECTS ON EARLY POSTNATAL-GROWTH OF LAMBSOF DIFFERENT GENOTYPES

Two important North European sheep breeds (the purebred Flemish Milksh eep (M) and Suffolk (S) breed) were double reciprocally crossed to dev elop a highly fertile ewe genotype (SM X MS or F2, called the K.U. Lov enaar), which was finally crossed with Texel sires to improve carcass and slaughter characteristics of the final slaughter lamb genotype: F3 or T X F2. Birth weight, birth date, litter size, number of suckling lambs, age of ewe and sex of lambs had a significant influence on earl y postnatal growth rate (P < 0.001). The significantly positive influe nce of birth weight on earliest postnatal growth rate diminished with increasing age of lambs. Age of ewes affected increases of lamb weight s by having an important effect on birth weight. Lambs of I-year-old e wes were characterized by a significantly lower birth weight and postn atal growth rate compared with lambs of multipareous ewes. A negative effect of litter size was observed on birth weight and on early postna tal growth results until 10 kg. Ram lambs had a higher birth weight an d realized better growth until 16 kg, compared with results of ewe lam bs, Significant effects of date of birth were also observed. Without c orrection for significant effects, variation in postnatal growth rate was about 30%. Growth rate of final slaughter lamb genotypes F3, T(MS) and T(F2fix) were significantly different. F3 and T(MS) lambs realize d a significantly lower growth rate at 16 kg;than T(F2fix) lambs !resp ectively, 324, 302 and 359 g day(-1)). However, the number of days nee ded to reach 16 kg was significantly higher for T(F2fix) lambs due to the low growth performance from 6 to 10 kg. F2 lambs had the highest g rowth rate of 370 g day(-1), while F2fix lambs realized the lowest pos tnatal growth: 283 g day(-1). Variation in postnatal growth rates decr eased after correction for the significant effects. Early postnatal gr owth performance of slaughter lamb genotypes T(MS), F3 and T(F2fix) we re comparable (about 320 g day(-1) at 16 kg), but were still significa ntly lower than the excellent growth rate of F2 lambs (404 g day(-1)). They did not differ in growth data from MS and F2fix lambs. For selec tion on early postnatal growth one has to take into account maternal a nd environmental influences.