Responses of seasonally anestrous gilts and weaned primiparous sows to treatment with pregnant mare's serum gonadotropin and Altrenogest

Abstract

Seasonal anestrus during late summer and autumn delays the onset of puberty in gilts and the prompt return to estrus in weaned sows. In this study, 132 gilts that had not been detected in estrus within 3 wk after being moved to the breeding barn were given a single intramuscular (i.m.) injection of 0, 363, 725, or 1088 IU of pregnant mare's serum gonadotropin (PMSG), or they were fed Altrenogest, a synthetic progestogen, (20 mg per day) for 14 d. Thirty eight percent of control gilts were detected in estrus within 20 d after treatment. Treatment with 725 or 1088 IU PMSG or Altrenogest significantly increased the proportion of gilts detected in estrus within 20 d to 77% and significantly reduced the average interval to estrus. Treatment with 363 IU PMSG did not increase the percentage of gilts in estrus within 20 d. Primiparous sows (n = 155) were assigned to a 2 × 3 factorial experiment at weaning. The sows received 0 or 20 mg Altrenogest for 3 d beginning the day after weaning and 0, 900, or 1200 IU PMSG which was given the day after weaning or the day after the last dose of Altrenogest was administered. Fifty eight percent of control sows were detected in estrus within 10 d. Administration of 1200 IU PMSG alone increased the percentage of sows detected in estrus within 10 d to 95%. Treatment with 1200 IU PMSG plus Altrenogest or 900 IU PMSG with or without Altrenogest tended to increase the percentage of sows in estrus within 10 d (70 to 76%). Altrenogest alone was not beneficial. Fertility and subsequent litter sizes among gilts and sows that were given various treatments were similar. We concluded that a single intramuscular injection of an appropriate dose of PMSG overcomes seasonal anestrus in gilts and weaned primiparous sows.