Reproductive performance in two organic sheep farming systems differing by the number of mating sessions in and out of the breeding season

Abstract

Hormonal treatments to control ovulation and the intensification of reproduction rhythm are usual strategies to increase ewe productivity. However, in organic farming the use of hormones is banned, making any increase of reproduction rhythm an inappropriate practice. This work tested if increasing the number of mating sessions per year could improve ewe annual productivity, while maintaining a non-intensive reproduction rhythm of one lambing per ewe per year. Reproductive performance was studied over five years in two organic sheep farming systems differing by the number of mating sessions (MS) per year, two (2MS) or four (4MS). The 4MS system included two mating sessions in the breeding season (September and November) and non-breeding season (April and June). The 2MS system included mating in November and April. Non-pregnant ewes were recycled one (2MS) or two times (4MS system) on consecutive mating sessions. Considering all mating attempts per ewe individually (n = 1366), the time elapsed from mating to lambing (159 ± 0.2 days), fertility (86%), prolificacy (166%) and productivity (143%) did not differ between the systems (P > 0.05). Fertility, prolificacy and productivity were higher in the breeding than the non-breeding season (P ≤ 0.05), and in adults than young ewes (P ≤ 0.05), without interaction with the systems (P > 0.05). In the non-breeding season, fertility, prolificacy and productivity did not relate to ewe cyclic status (P > 0.05), whereas the time elapsed from mating to lambing was shortened in cyclic ewes (P ≤ 0.05). Good ewe body condition at lambing and mating and dynamic gain in body condition from drying to mating improved productivity (P ≤ 0.05) by increasing fertility or prolificacy regardless of the system (P > 0.05). On a yearly scale, the number of lambed ewes was higher in the 4MS than the 2MS system (91% vs 85%; P ≤ 0.05) leading to higher ewe annual productivity (154% vs 141%; P ≤ 0.05). The percentage of ewes that were recycled on consecutive mating sessions was higher in the 4MS than the 2MS system (24% vs 18%; P ≤ 0.05), possibly explaining the 4MS increase of ewe annual productivity by extending mating opportunities for the ewes. The increase in the number of mating sessions per year is a hormone-free strategy suitable for organic sheep farming systems to improve annual ewe productivity on a basis of one lambing per ewe per year. This approach proved beneficial to compensate for lower fertility in the non-breeding season, especially for young ewes.

Keywords: Organic farming; Reproductive performance; Seasonal reproduction; Sheep; System.