Efficacy of exogenous gonadotrophic hormones to induce estrus in anestrous gilts

The objective of this study was to examine the response of anestrous gilts to injections of pregnant mare's serum gonadotrophin (PMSG) alone or in combination with human chorionic gonadotrophin (hCG). One hundred and eighty gilts which had failed to exhibit estrus by about 33 wk of age were given one of the following treatments: no injection, 500 IU PMSG, 1000 IU PMSG or 400 IU PMSG + 200 IU hCG. A greater number of gilts injected with 1000 IU PMSG exhibited estrus within nine days of treatment than control gilts (21/37 vs 13/41, X(2) = 5.0, P<0.05). In addition, gilts injected with 1000 IU PMSG exhibited oestrus significantly earlier than gilts receiving the other treatments. In comparisons of the proportion of gilts ovulating within 9 d of treatment and the treatment-to-ovulation interval, there were no significant differences between the three exogenous hormone treatments. There was also no significant effect of treatment on farrowing rate or subsequent litter size. The results of our study indicate that treatment of anestrous gilts with 1000 IU PMSG effectively induces ovulation and fertile estrus. Inadequate expression of estrus often accompanied the ovulation induced by the lower dosages of PMSG used with and without hCG in this experiment.