ESTRUS AND PREGNANCY IN PRIMIPAROUS SOWS TREATED WITH PREGNANT MARE’S SERUM GONADOTROPIN OR ESTRADIOL-17β AND PROGESTERONE

Abstract

Over a 3-yr period, the effectiveness of pregnant mare’s serum gonadotropin (PMSG-1,500 IU) or estradiol-17β (1 mg) plus progesterone (2 mg) for the stimulation of post-weaning estrus and conception in primiparous sows from a herd with a history of post-weaning anestrus was evaluated. On the day after weaning, an intramuscular (i.m.) injection of PMSG or steroids was given to 49 and 51 sows, respectively. Fifty untreated sows served as controls. Treated sows in estrus by day 8 and control sows in estrus by day 40 were bred on the 2nd day of estrus. Serviced sows were killed at day 25 of pregnancy or on the day after return to estrus. The remaining sows were killed when in estrus or between days 41 and 45 after weaning. By day 8, more (P < 0.01) PMSG-treated (98.0%) sows were in estrus than either the steroid-treated (64.7%) or control (66.0%) sows. By day 14, fewer (P < 0.05) steroid-treated than control sows were in estrus (64.7 vs. 82.0%). The mean interval between weaning and estrus for sows in estrus by day 8 was less for the PMSG (P < 0.01) - and steroid (P < 0.05) - treated sows than for the control sows (3.83 ± 0.11 and 4.36 ± 0.28 vs. 5.12 ± 0.23 days). For the steroid-treated and control sows in estrus after day 8, the mean time to estrus was 34.6 ± 3.5 and 21.2 ± 2.8 days, respectively (P < 0.01). Pregnancy rates were similar for the PMSG and steroid treatments (57.1 and 47.0%), and lower than for the control sows (84.0%). The PMSG-treated animals had larger litters (16.4 ± 1.0 embryos) than either the steroid-treated (12.8 ± 1.1 embryos) or control (11.3 ± 0.8 embryos) animals.