Merck Animal Health

Lancaster R.T., Foxcroft, G.R., Boland, M.R, Edwards, S. and Gordon, I., 1985. Fertility of sows treated with exogenous estradiol and/or gonadotropins to control postweaning estrus. Anim. Reprod. Sci., 8:365-373 In the first of two experiments 28 multiparous sows were allocated to one of the following treatments two days after weaning at approximately 35 days postpartum: (1) untreated; (2) i.m. injection 10 μg estradiol benzoate (OB)/kg body weight (b. wt.); and (3) i.m. injection 20 μg OB/kg b. wt. Sows were bred at first post-weaning estrus and ovulation rate assessed at slaughter. The mean interval from weaning to estrus in each group was: (1) 5.6 ± 0.2; (2) 4.7 ± 0.2; and (3) 4.7 ± 0.2 days; the mean ovulation rates in groups 1 and 2 (18.7 ± 0.6 and 17.4 ± 1.8, respectively) were significantly higher (P < 0.01) than that of 12.0 ± 1.7 for treatment three sows. Two untreated and one each of the treated sows were not cycling at slaughter. In the second experiment 75 multiparous sows weaned at 28 ± 3 days postpartum (day 0) were evenly allocated with respect to parity to one of four treatment groups: (1) untreated; (2) i.m. injection 10 μg OB/kg b. wt. on day two; (3) P.G. 600 (400 I.U. PMSG + 200 I.U. HCG) injection subcutaneous day 0; and (4) combined P.G. 600/OB treatment as in (2) and (3) above. Sows were bred naturally at the first post-weaning estrus and fertility assessed at farrowing. Control animals had a significantly longer (P < 0.05 weaning to estrus interval (4.53 ± 0.25 days) compared to treatment 2 (4.03 ± 0.13), treatment 3 (3.97 ± 0.12) and treatment 4 (3.81 ± 0.07) sows. Sows treated with P.G. 600 alone showed a significant increase (P < 0.05) in numbers born live compared to pre-treatment values. A smaller and nonsignificant increase in numbers born live in control sows (probably related to increasing parity) was not observed in either OB or P.G. 600/OB-treated animals. These results suggest that with further modification of the treatments, a system may be developed for introducing fixed-time artificial insemination (AI) or mating as a means of controlling the reproductive performance of the weaned sow.