Ovarian follicular development, estrus, and ovulation in seasonally anestrous sows treated seven days post weaning with equine and human chorionic gonadotropins

A rapid return to estrus after weaning maximizes productivity in sow herds. Return to estrus is influenced by season and production factors (eg, parity and body condition).1-4 The effects of season and production factors on postweaning interval to estrus are mediated by ovarian follicular development.5,6 Sows with small follicles (< 4 mm) at day 3 after weaning were more likely to experience anestrus or delayed estrus compared to sows with larger follicles.5 High ambient temperature during lactation was associated with suppressed follicular growth and delayed the return of normal follicular populations after weaning.7 Restoring compromised follicular growth in anestrous sows should improve the percentage of sows in estrus after weaning. An injectable mixture of equine chorionic gonadotropin (eCG; 400 IU per mL) and human chorionic gonadotropin (hCG; 200 IU per mL) was developed specifically for the purpose of stimulating follicular growth in sows and gilts (P.G. 600; Intervet, Millsboro, Delaware). This application is widely used on swine farms.8,9