Gilts not detected in estrus in a batch farrowing breeding herd: a hormonal strategy to improve gilt utilization

This study evaluated reproductive performance of gilts classified as in anestrus in a batch farrowing system. Thirty-three gilts not expressing estrus within 40 days post-arrival were treated with chorionic gonadotropins, with blood collected for progesterone (P4) analysis on the same day. Thirteen gilts expressed estrus within 7 days, and 12 were inseminated (232.8 ± 2.1 days old), with 11 farrowing (91.7%; 14.2 ± 0.83 total piglets). Nineteen gilts had P4 ≤ 2.6 ng/mL at treatment; among the 20 non-responders, 10 had P4 > 2.6 ng/mL. A strong association was observed between P4 levels (≤ 2.6; > 2.6 and < 19; ≥ 19 ng/mL) and the responsiveness of gilts to gonadotropin treatment (P < 0.01; Cramér's V = 0.63), with greater responsiveness in gilts with P4 levels ≤ 2.6 ng/mL. Non-responsive gilts (n = 20) received Altrenogest for 10 - 11 days, with 17 showing estrus within 10 days and 15 farrowing (88.2%; 14.3 ± 0.84 total piglets). Estrus detection failures and silent heat likely caused misdiagnosis. Gonadotropin, with or without Altrenogest, reduced culling ~8-fold, allowing 41-58% of gilts to reach at least the 3^rd farrowing.