GENETIC AND PHENOTYPIC ASPECTS OF THE GROWTH CURVE CHARACTERISTICS INMEHRABAN IRANIAN FAT-TAILED SHEEP

Brody's growth function was fitted to body weight-age data from 1281 M ehraban Iranian fat-tailed lambs (432 males, 849 females and 18 sires) , progeny of 18 rams and 660 ewes, to study the genetic and phenotypic aspects of growth curve parameters and derived traits. Estimates of m ature weight, rate of maturing and weight from birth to 48 months were obtained by least-squares procedure. Year of birth, sex, sire and typ e of birth significantly influenced all growth curve parameters. Year of birth, sire, age of dam, sex and type of birth significantly affect ed the pre-weaning growth period (90 days), while the major source of variation in post-weaning growth were sex, year and sire. The heritabi lity of mature weight was 0.52, and the heritabilities of other weight s recorded ranged from 0.28 to 0.48. The genetic and phenotypic correl ations between mature weight and immature weights were all positive an d ranged from 0.17 to 0.61, and from 0.08 to 0.95, respectively. Genet ic and phenotypic correlations were generally positive among weights a t all ages. A phenotypic and genetic antagonism between mature weight and rate of maturing was found, indicating that earlier maturing lambs would have lighter mature weights than late maturing lambs. The resul ts indicated that selection for 6-month weight or later will result in a correlated response in mature weight. (C) 1998 Elsevier Science B.V . All rights reserved.