Genetic and phenotypic aspects of the growth curve characteristics in Mehraban Iranian fat-tailed sheep

Brody's growth function was fitted to body weight-age data from 1281 Mehraban 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 mature weight, rate of maturing and weight from birth to 48 months were obtained by least-squares procedure. Year of birth, sex, sire and type of birth significantly influenced all growth curve parameters. Year of birth, sire, age of dam, sex and type of birth significantly affected the pre-weaning growth period (90 days), while the major source of variation in post-weaning growth were sex, year and sire. The heritability of mature weight was 0.52, and the heritabilities of other weights recorded ranged from 0.28 to 0.48. The genetic and phenotypic correlations between mature weight and immature weights were all positive and ranged from 0.17 to 0.61, and from 0.08 to 0.95, respectively. Genetic and phenotypic correlations were generally positive among weights at 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 results 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.