Reproductive performance in primiparous sows after postweaning treatment with a progestagen

The purpose of this study was to determine whether administration of altrenogest (Regumate; Roussel-Uclaf, París, France) to primiparous sows would improve estrus synchronization rate and reproductive efficiency of the herd, measured in terms of the weaning-to-estrus interval (WEI), the weaning-to-first-fertile-estrus-interval (WFEI), rate of sows repeating estrus, and conception rate at first estrus. First-parity sows (Landrace × Large White) from a commercial herd received altrenogest, 20 mg per sow per day, for 5 consecutive days starting the day after weaning. A group of untreated sows acted as controls. The percentage of sows showing estrus 4 to 7 days postweaning (controls; 65.6%) or 4 to 7 days after treatment ended (8 to 11 days postweaning) was higher (P < .05) in the altrenogest-treated group (86.2%). Sows were mated naturally twice at the first estrus after weaning and pregnancy was diagnosed by ultrasonography 23 to 24 days later. There were no differences between treated and control sows in means of WEI, WFEI, rate of sows repeating estrus, or conception rate to first service. Litter size at farrowing, number of live born piglets, number of stillborn piglets, preweaning mortality, and weaned litter size were also similar between groups.