LATE-LACTATION ALTRENOGEST ADMINISTRATION MITIGATES POST-WEANINGOESTRUS ALTERATIONS IN LOOSE-HOUSED SOWS WITH HIGH LITTER LOSSES

Introduction and Objectives The progressive adoption of loose-housing systems for lactating sows in Europe aims to improve animawelfare but is often associated with increased piglet mortality due to crushing. In addition to welfare anproductivity concerns, substantial litter loss may abruptly reduce suckling stimulation, potentially inducing stress-related neuroendocrine response and premature ovarian activity during lactation. This condition macompromise the normal resumption of oestrus after weaning. The present study evaluated whethealtrenogest administration during late lactation infl uences post-weaning oestrus expression in loose-housesows experiencing marked pre-weaning litter losses. Materials and Methods One hundred loose-housed sows (parity 1–8), temporarily confi ned only around parturition, were enrolledSows were included when cumulative litter losses before weaning reached at least 30% of an initial averagof 13.8 ± 1.6 live-born piglets, occurring at 6 ± 1 days pre-weaning. Animals were randomly allocated to Control or Treated group. Treated sows received oral altrenogest (5 mL/day) starting on the day the litteloss threshold was reached and continuing until one day prior to weaning. The weaning-to-oestrus interva(WOI) and the proportion of sows returning to oestrus within 7 days post-weaning (RO7) were recorded ananalyzed using Kruskal–Wallis and chi-square tests. Results and Discussion Sows receiving altrenogest exhibited a signifi cantly shorter WOI compared with controls (4.11 ± 3.8 vs 9.± 14.2 days; p = 0.011). In addition, the proportion of sows expressing oestrus within 7 days after weaninwas higher in the treated group than in the control group (97.2% vs 81.6%; p = 0.027). In loose-housed sowexperiencing substantial litter losses, late-lactation altrenogest administration was associated with aimproved and more synchronized post-weaning return to oestrus. It can be hypothesized that reducesuckling intensity following litter loss may weaken inhibitory control over gonadotrophin secretionpredisposing to ovarian activation during lactation and delayed behavioural oestrus after weaning. Conclusion Although endocrine pathways were not directly investigated, altrenogest treatment may havcounterbalanced this premature activation, supporting a coordinated ovarian rebound at weaning. Undethe conditions of this study, this approach appears promising for maintaining reproductive eff iciency iwelfare-oriented farrowing systems.