Treatment with chorionic gonadotropins during lactation inhibits post-weaning estrus expression in sows

This study evaluated the efficiency of protocols using two different dosages of eCG and hCG administered during lactation to delay post-weaning estrus expression in sows. Sixty-two sows were selected on D-14 (D0 = weaning) and allocated to one of three treatments: Control (n = 20; saline administration on D-7 and D-4); 500 IU (n = 21; 500 IU eCG on D-7 and 500 IU hCG on D-4); and 1000 IU (n = 21; 1000 IU eCG on D-7 and 1000 IU hCG on D-4). Estrus detection was performed twice daily after weaning, and blood samples were collected on D-7, D-1, D+6, and D+13. On D+15, the sows were slaughtered for ovarian evaluation. The percentage of sows detected in estrus post-weaning was greater in the Control group (90.0%) compared to the 500 IU (23.8%) and 1000 IU (9.5%) groups (P < 0.01). The proportion of sows with corpus hemorrhagicum and/or corpus luteum and the total number of corpora lutea at slaughter were similar among treatments (P ≥ 0.41). On D+6, serum progesterone (P4) concentration was lower in the Control group than those in the 500 IU and 1000 IU groups (P < 0.01). Administration of 500 or 1000 IU of eCG and hCG during lactation effectively induced the formation of corpora lutea and sustained high serum P4 levels for at least 13 d post-weaning, thereby inhibiting estrus expression in 76 to 90 % of treated sows.