LITTER LOSSES IN LACTATING LOOSE HOUSED SOWS: ALTRENOGEST PREVENTS IMPAIRED OESTRUS

Background and Objectives Modern European pig production systems are increasingly focused on sow welfare, and many herds are moving towards the abandonment of farrowing crates. However, this transition is associated with a higher risk of piglet crushing. Beyond the productive and welfare implications, a sudden reduction in suckling stimulation may also trigger a neuroendocrine stress response in the sow, potentially leading to premature ovarian activation during lactation and altering the resumption of post-weaning oestrus. This study aimed to evaluate the effect of altrenogest administration during late lactation on post-weaning oestrus expression in sows experiencing partial litter loss. Material and Methods A total of 100 loose housed sows (parity 1–8) were included in the study, with temporary confinement limited to the periparturient period. Animals were recruited when cumulative pre-weaning litter losses reached 30% of an average of 13.8±1.6 live-born piglets prior to weaning (6±1 days), and were randomly assigned to Control or Treatment (5mL altrenogest, Virbagest®, Virbac, orally once daily starting from the day when cumulative litter losses first reached 30% until one day before weaning). Weaning-to-oestrus interval (WOI) and return-to-oestrus rate within 7 days after weaning (RO7) were recorded and analyzed (Kruskal–Wallis and chi-square test). Results The treated group showed a significantly shorter WOI compared to control (4.11±3.8 vs 9.8±14.2 days; p=0.011). The RO7 was higher in the treatment group (97.2% vs. 81.6% in controls; p=0.027). Discussion and Conclusion The shorter WOI observed in treated sows may be hypothesized to be related to the endocrine consequences of partial litter loss. Reduced suckling may decrease inhibitory feedback on GnRH and LH secretion, potentially predisposing ovulation during lactation and delayed visible oestrus after weaning. Although endocrine mechanisms were not directly assessed, altrenogest administration during late lactation may have counteracted this premature activation, supporting ovarian rebound synchronization with weaning under the study conditions.