High body condition score combined with a reduced lambing to ram introduction interval improves the short-term ovarian response of milking Lacaune ewes to the male effect

Abstract

The male effect is an effective natural technique to induce off-season ovulation and ultimately mating or artificial insemination in small ruminants. It constitutes an alternative to hormonal treatments in conventional breeding systems and, to shift and organise the yearly production cycle, is currently the only solution complying with European organic standards. However, its associated performances are still heterogeneous, both in terms of the global response and the extent of reproductive synchronisation of the females, due to complex interactions with environmental factors that limit its use on commercial farms. This study was carried out on a French organic farm under commercial conditions to investigate, in the field and across five consecutive years, the main parameters affecting the early ovarian response to a ram effect on Lacaune dairy ewes. While the within-year binary logistic regressions yielded contrasting results, the cross-year mixed-effect binary logistic regression models clearly showed that parameters associated with the nutritional state of the animals have a profound influence on the ovarian response of the ewes. Indeed, the probabilities of a spontaneous resumption of ovarian activity before the ram effect and of an early ovarian response to the ram effect were positively associated with the body condition score, total milk production and the age of the animals, while being negatively associated with the milk production level at the 3rd milk recording. The probabilities of a spontaneous resumption of ovarian activity before the ram effect were positively associated with the interval between lambing and the introduction of the rams. Altogether, these results indicate that the ovarian performances in response to a male effect follow a bell-curve pattern with optimal performances depending upon a complex combination between photoperiodic and nutritional cues. Regarding these latter, this study highlights the major contribution of body reserves and energy balance dynamics.