Genetic parameters for body weights in Timahdite sheep were estimated using records of 10370 lambs from the ‘Société Nationale de Développement de l’Elevage’ born in 1988-89 to 1998-99. An animal model with derivativefree restricted maximum likelihood procedures was used. Random effects were direct and maternal additive genetic, maternal permanent environmental, and error. Direct and maternal heritability estimates were 0·05 and 0·05 for birth weight, 0·02 and 0·07 for weight at 30 days, 0·07 and 0·08 for weight at 70 days, 0·06 and 0·01 for weight at 90 days. Estimates of fraction of variance due to maternal permanent environmental effects were close to zero, except for weight at 90 days. Genetic correlations between direct and maternal genetic effects were –0·55, –0·51, –0·50 and –0·17 for body weights at birth, 30, 70 and 90 days, respectively. Estimates of direct genetic correlations among body weights were positive and high, ranging from 0·69 to unity. Phenotypic correlations were positive and moderate to high, being lower than their corresponding direct genetic correlations. Estimates of correlations between maternal genetic effects among weights were positive and high, varying from 0·79 to unity. Cross-correlations between direct genetic effects for one weight and maternal genetic effects for another weight were consistently negative, ranging from –0·05 to –0·63. These results indicate that selecting for improved maternal and/or direct effects in Timahdite sheep is expected to generate only slow genetic progress in terms of early growth.

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L’étude a porté sur la comparaison des productivités des brebis Timahdite et croisées D’man x Timahdite (DxT) en station et chez quatre éleveurs privés pratiquant le croisement industriel. Ainsi, une dizaine de brebis gravides DxT nées à la station ont été cédées à chaque éleveur. Au total, 131 performances de reproduction des brebis Timahdite et croisées DxT, et 188 performances de croissance et de viabilité des agneaux issus du croisement entre ces brebis et des béliers de race Ile-de-France ont été analysées. Les performances de reproduction des brebis DxT ont été supérieures à celles des brebis Timahdite, sauf pour le poids de portée à 70 jours. La taille de portée à la naissance, à 70 jours et le poids de portée à la naissance des brebis DxT ont été respectivement de 0,49 agneau, 0,32 agneau et 0,29 kg plus élevés que ceux des brebis Timahdite. Cependant, ces écarts ont été plus importants dans les élevages privés qu’en station. Les poids de portée à 70 jours des deux types génétiques n’ont pas été statistiquement différents. Pour les performances de croissance des agneaux, la race de la mère n’a eu d’effet significatif que sur le poids à 70 jours. Les agneaux issus de mères Timahdite ont pesé en moyenne 2,60 kg de plus que les agneaux nés de mères DxT. La différence entre ces deux catégories d’agneaux a été plus élevée en station (3,30 kg) que chez les éleveurs privés (1,6 kg). En conclusion, les brebis DxT ont réalisé chez les éleveurs des performances généralement plus élevées que les brebis Timahdite qui sont souvent utilisées comme support de croisement.

-The reproductive performance of 1117 Timahdite and D'man × Timahdite (D × T) ewes lambing in the autumn, spring and summer, and weights and survival to 90 days of their 968 lambs were evaluated. All ewes were exposed to Meat Lacaune rams. The lambing rate of Timahdite ewes was 42% lower than that of D × T ewes. The litter size at birth and at 90 days of D × T ewes was 0.23 and 0.19 lamb, respectively greater than those of Timahdite ewes. D × T crossbred ewes weaned 4.1 kg weight more than Timahdite ewes. The lambing rate, litter size at 90 days and litter weight at birth and at 90 days of summer-lambing ewes were 43%, 0.39 lamb, 0.23 kg and 17.7 kg, respectively lower than those of autumn-lambing ewes. They were also 25%, 0.49 lamb, 1.3 kg and 14.6 kg, respectively lower than those of spring-lambing ewes. The dam's genetic group had significant effects on lamb birth weight, but not on weight at 30 days and 90 days and survival. Spring-born lambs had the highest birth weight and survival, and autumn-born lambs had the highest weight at 30 days and 90 days. It was concluded that D × T crossbred ewes had better productivity than Timahdite ewes at any lambing season. Furthermore, flocks that rely on pasture for their nutrition should avoid summer lambing, which results in low ewe and lamb performance.