Revue d’Elevage et de Médecine Vétérinaire des Pays Tropicaux (Jan 2009)
Non-Genetic Factors of Variation of the Productivity of the Noire de Thibar Ewe
Abstract
An initial database containing growth records of 101,000 lambs obtained within the context of the national meat sheep improvement program was used to quantify reproductive and productivity (total litter weight) traits of ewes of the Noire de Thibar breed, and to determine the influence of non-genetic factors on these traits. A database was then generated: it comprised 64,137 lambings over a 12-year period (1991-2002), and 25 farms and 48 flocks. The mean fertility rate in the flocks was 80.1 ± 12.9% with highly significant effects (p < 0.001) of the farm and lambing year. At birth, the average litter size per lambing ewe was 1.32 ± 0.47. It dropped to 1.23 ± 0.55 at 70 days after lambing. All main sources of variation (farm, lambing year, lambing month, and dam age) retained in the model as well as their interactions significantly affected the litter size at different stages after lambing. Survival of all the lambs in the litters between birth and 70 days post-lambing was observed in 89.9% of the ewes. Entire loss of the litter was observed in only 5.8% of the ewes. An analysis of variance revealed that factors such as the lambing year, lambing month, dam age, sex of the litter, and litter size at birth had a highly significant effect on the proportions of ewes with different levels of lambs’ survival within litters. On average, the productivity of the Noire de Thibar was 6.6 ± 2.2, 10.3 ± 3.5 and 18.6 ± 6.6 kg at 10, 30 and 70 days after lambing, respectively. The main factors of variation (farm, lambing year, lambing month, dam age, litter size), and some second-level interactions had highly significant effects (p < 0.001) on the studied productivity traits. Ewes aged four years and which had male triplets yielded the highest productivities at 70 days after lambing. This preliminary work on the reproductive and productivity traits of Noire de Thibar ewes is essential to develop a ewe selection index as part of a genetic improvement scheme for this breed.
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