Reproductive Performance of Gilts After Different Periods of Altrenogest Treatment in a Batch Farrowing Breeding Herd

Altrenogest is widely used for synchronising gilt breeding groups. On-farm constraints often require adjusting supplementation duration depending on cycle monitoring and batch intervals; however, the reproductive impact of these shorter regimens remains unclear. This retrospective study evaluated the reproductive performance of gilts treated with Altrenogest for different durations in a batch farrowing breeding herd. Gilts (~166 days old at arrival) that exhibited their first estrus within 40 days post-arrival were allocated to three treatments: ALT 6-14 (n = 166), receiving Altrenogest for 6-14 days; ALT 15-21 (n = 190), receiving Altrenogest for 15-21 days and Control, receiving no treatment (n = 175). Altrenogest supplementation started on days 11-12 after their last estrus (first or second). Insemination for ALT gilts was performed at the first estrus following treatment (~231 days old). For Control gilts, insemination occurred in the third or fourth estrus (~230 days old). Approximately 98% of the ALT gilts exhibited estrus, whereas 10.3% of the Control gilts did not display estrous signs within the breeding window. The interval from the end of the Altrenogest treatment to estrus expression was slightly longer (p = 0.05) in ALT 15-21 (6.6 ± 0.2 days) than in ALT 6-14 (6.4 ± 0.2 days). Adjusted farrowing rate and total litter size did not differ among treatments (p ≥ 0.69). The duration of Altrenogest supplementation did not affect estrous cycle synchronisation efficiency or the reproductive performance of gilts. The strategic use of Altrenogest enables a reduction in labour and costs by allowing progestogen supplementation for fewer than 14 days.