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Knowledge of genetic parameters for growth traits of economic importance is required for the development of sheep populations in Morocco. Records on 544 lambs of the Timahdite (T) breed and of 756 D'man x Timahdite (DT) lambs, all born from 1992 to 1998, were used to estimate genetic parameters for lamb weights at birth, at 30, 70 and 90 days and daily gains from 10-30 days, 30-70 days and 30-90 days for each trait. Separate REML (co)variance component estimates were obtained assuming animal models that included the fixed effects of birth year, sex, age of dam, birth type or rearing types and the interaction of birth year by sex, the animal direct genetic effect and the maternal genetic effect. Genetic and phenotypic correlations between traits were estimated with models including the same fixed effects and only additive direct genetic effects. All fixed effects influenced growth traits. The direct heritability estimates for the various body weight and daily gain traits were low to medium and varied between 0.07 and 0.25 in T, and between 0.02 and 0.18 in DT. Maternal heritability ranged from 0.20 to 0.36 in DT, and from 0.01 to 0.10 in T lambs, except for the birth weight (0.53). For all traits the direct and maternal genetic correlations were high and negative in DT (-0.80 and -1.00) and in T (-0.90 and -1.00) lambs. However, the accuracy of such estimates is low due to the small data set used in the present study. The estimates of genetic and phenotypic correlations were positive for all traits, they were particularly high for genetic correlations between weights and weight gains after birth, both in DT and T lambs, and they showed no genetic antagonisms among the growth traits.

Effets du milieu et génétiques sur la croissance des agneaux Timahdite et croisés au Maroc