Controlling reproduction in organic sheep breeding: the influence of breeding factors on the effectiveness of the ram effect

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Summary

The ram effect, which is a natural method for the control of reproduction in sheep, is an alternative to hormone treatments that are banned on organic farms. The ram effect induces a combination of ovulation and oestrus in ewes that is acyclic and conducive to artificial insemination. The proportion of acyclic females with induced ovulation and their subsequent fertility at the first oestrus is variable. The control of some breeding factors that have been studied here may help to reduce this variability. The proportion of ewes induced to ovulate by rams increased as the season advanced (54% in April vs. 84% at the end of May, p<0.05) and with a longer time period between drying-off and mating: from 29% to 84% (p<0.001) for 22 and 86 days elapsed, respectively. The fertility of these ewes at the first oestrus was also higher at the end of May than in April (86% vs. 39%, p<0.01) and increased with the amount of time elapsed since drying-off (55% and 81% for 22 and 86 days, respectively; p=0.09). The time that the first oestrus occurs is later for lean ewes because they have a higher proportion of short cycles (67%) than fat ewes (41%, p<0.05).

Summary translation

Une des façons d’améliorer l’efficacité de l’effet bélier est de se placer dans de bonnes conditions d’élevage. Ainsi, la proportion de brebis dont l’ovulation est induite augmente lorsque la date d’introduction des mâles est plus tardive (55% en avril vs 81% fin mai, p<0,05) et avec l’allongement de l’intervalle entre le tarissement et la mise en lutte : de 29% à 84% (p<0,001) pour des intervalles respectifs de 22 et 86 jours. La fertilité de ces brebis est également meilleure fin mai qu’en avril (86% vs 39%, p<0,01) et lorsque l’intervalle écoulé depuis le tarissement est accru : respectivement 55% et 81% (p=0,09). Enfin, le moment d’apparition des premières ovulations fertiles est retardé chez les brebis en état corporel faible car elles présentent davantage de cycles courts (67%) que les brebis en bon état (41%, p<0,05).

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