Response to gonadotrophins differs for gilts from female- and male-biased litters

- The sex ratio of a gilts birth litter may affect their lifetime performance.
- Gilts from male-biased litters were more likely to ovulate than gilts from female-biased litters.
- They also had a higher number of corpora lutea.
- The sex ratio of the birth litter could be used to select breeders.

In several species, females masculinised by abnormal androgen exposure in utero have poor reproductive performance and gilts born into litters with a male bias are likely exposed to greater androgen concentrations prenatally than gilts born into female-biased litters. At 24 h of age, piglet plasma testosterone concentrations in gilts from male-biased litters (>60% male; n = 22) or female-biased litters (>60% female; n = 27) were not different. At 18 wks of age, all gilts received an injection of 400 IU equine chorionic gonadotrophin plus 200 IU human chorionic gonadotrophin to stimulate oestrus. Two weeks after the injection gilts were slaughtered and ovaries collected for determination of numbers of corpora lutea (CL). Compared to gilts from female-biased litters, gilts from male-biased litters were more likely to ovulate (86.0% vs 59.5%, P = 0.047) and had more CL (13.1 ± 1.5 vs 7.2 ± 1.7, P = 0.015). The present data indicate an effect of birth litter sex-bias on pre-pubertal physiological development, possibly involving organisational effects at the ovarian cellular level impacting on future ovarian function. Potential impacts on subsequent fertility remain to be determined.