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Abstract : |
Growth data recorded on 10244 Noire de Thibar lambs born along five years and raised in ten flocks in North-Western region of Tunisia were used to carry out this study. The analysis of variance has shown that herd, sex-type of birth and herd by date of birth interaction had highly significant effects on the lamb growth. Males born single were heavier and grew faster than the other sex-type of birth categories. However, twin or multiple males were less heavy than females born single. Age of dam had a significant effect only from birth to seventy days. The birth date, as well as the interaction among herd and sex-type of birth affected significantly all studied traits except the average daily gain between 70 and 90 days. Multiplicative adjustment coefficients were computed for sex-type of birth and age of dam factors. Heritability of each growth trait was estimated by an adjusted regression dam-offspring method. Genetic and phenotypic correlations between the traits were also estimated. Such parameters should be essential information for developing genetic evaluation tools and/or elaborating genetic improvement programs, especially, if we consider that the present selection practice remains empirically based on a biased average daily gain between 10 and 30 days., |
