Environmental and maternal effects on early postnatal growth of lambs of different genotypes

Abstract

Two important North European sheep breeds (the purebred Flemish Milksheep (M) and Suffolk (S) breed) were double reciprocally crossed to develop a highly fertile ewe genotype (SM × MS or F2, called the K.U. Lovenaar), which was finally crossed with Texel sires to improve carcass and slaughter characteristics of the final slaughter lamb genotype: F3 or T × F2. Birth weight, birth date, litter size, number of suckling lambs, age of ewe and sex of lambs had a significant influence on early postnatal growth rate ( P < 0.001). The significantly positive influence of birth weight on earliest postnatal growth rate diminished with increasing age of lambs. Age of ewes affected increases of lamb weights by having an important effect on birth weight. Lambs of 1-year-old ewes were characterized by a significantly lower birth weight and postnatal growth rate compared with lambs of multipareous ewes. A negative effect of litter size was observed on birth weight and on early postnatal growth results until 10 kg. Ram lambs had a higher birth weight and realized better growth until 16 kg, compared with results of ewe lambs. Significant effects of date of birth were also observed. Without correction 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 realized a significantly lower growth rate at 16 kg than T(F2fix) lambs (respectively, 324, 302 and 359 g day −1). However, the number of days needed 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 growth rate of 370 g day −1, while F2fix lambs realized the lowest postnatal growth: 283 g day −1. Variation in postnatal growth rates decreased after correction for the significant effects. Early postnatal growth performance of slaughter lamb genotypes T(MS), F3 and T(F2fix) were comparable (about 320 g day −1 at 16 kg), but were still significantly 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 selection on early postnatal growth one has to take into account maternal and environmental influences.