Paramètres phénotypiques et génétiques des caractères de croissance et de reproduction des brebis croisées Berrichon du Cher x Romanov F1 à F4

This study intends to compare the performance of growth and the maternal aptitudes of F1 to F4 ewes issue of crossbreeding between the two parental breeds . Romance and Berrichon du Cher. The least-squares analysis of variance has been achieved on 1 298 ewes born from 1973 to 1977 and recorded until 1979. The original system of reproduction includes the first mating in may at 15 months (fertility : 0.86), the second post-partum mating in october at 20 months (fert. 0.82), and the following matings once a year in july august (fert. 0.97 to 0.99). The recorded performances at lambings 1 to 4 are respectively : 1.67, 1.87, 1.98 and 2.01 for the litter size ; 54.5, 57.0, 62.8 and 65.6 kg for the weight at lambing ; 1.53, 1.66, 1.95 and 2.01 kg for the average daily weight of milk suckled by the lambs during the first month of lactation. The differences between generations F1 to F4 are significant for the weight at 70 and 90 days (given that the initial growth is lower in F1 ewe lambs) but not significant for the 30-70 day weight gain. They are not significant for the weight at lambing, the fertility, the number of lambs born and alive at lambing and the milk production of the ewes. This result confirms the previous observations obtained on F1 and F2 ewes, born from 1970 to 1972 and mated at the traditional time ; it demonstrates the lack of « regression » of performances from F1 to F4 in our conditions (Romanov as parental breed, no selection before the 4th generation). The birth-rearing class of the ewe has a significant influence on the lambing weight until 4 years and on the litter size at first lambing, giving an advantage of 0.1 lamb in favour of single born ewes. The heritability of performance has been estimated separately on F2 and F3 ewes by half sister analysis. The heritability of 30-70 day weight gain (0.17 and 0.43) is higher than the one relating the litter size (0.09 and 0.24) and milk production (0 and 0.16) at first lambing. The 30-70 day weight gain of ewe lambs is the character which has the higher genetic correlation with litter size at first lambing. Cette étude a pour but de comparer les performances de croissance et les aptitudes maternelles des brebis F1 à F4 issues du croisement entre les 2 races parentales Romanov et Berrichon du Cher. L’analyse des moindres carrés a été réalisée sur 1 298 brebis nées de 1973 à 1977 et contrôlées jusqu’en 1979. Le système original de reproduction comporte une première lutte en mai à 14 mois (fertilité