GENETIC AND PHENOTYPIC PARAMETERS OF EARLY GROWTH TRAITS OF LAMBS REARED ARTIFICIALLY IN A CONTROLLED ENVIRONMENT

This study involved body weights of 6078 lambs from 525 sires of two synthetic dam strains developed at the Animal Research Centre with 50% Finnish Landrace background. Breeding was practiced in flocks A and B for lambing at 4-mo intervals under an 8-mo breeding cycle. Lambs were housed indoors in a controlled environment on expanded metal floors in windowless barns, reared artificially with milk replacer and solid diet from birth to weaning at 21 days of age. Thereafter, all lambs were fed solid diet to 70 days of age. Paternal half-sib estimates of heritability for lamb weights at birth, weaning, 49 and 70 days of age were 0.25–0.26. Heritability estimates in the two synthetic dam strains were in close agreement (P > 0.05). Genetic and phenotypic parameter estimates did not demonstrate any significant linear trends across lambing periods. The moderate levels of heritability estimates for lambs reared artificially under a controlled environment suggest that genetic response to selection could be enhanced by selecting lambs independent of potential maternal effects and competition among litter mates for a fixed quantity of milk. Estimates of genetic and phenotypic correlations among various lamb weights ranged from 0.60 to 1.00, and from 0.51 to 0.93, respectively. Lamb weights having closer proximity in time showed higher correlations. Moderate to high genetic correlations between body weight of lambs at different ages indicated that selection for weight at one age should cause no adverse effects on body weight at other ages. Key words: Sheep, artificial rearing, lamb weights, heritability, genetic and phenotypic correlations