Anogenital distance reflects the sex ratio of a gilt’s birth litter and predicts her reproductive success1

Abstract

Anogenital distance (AGD) has been used to reflect masculinization in litter-bearing species. As masculinization affects behavior and reproduction, AGD could be measured to assist in selecting gilts with a temperament more suited to commercial production and greater reproductive potential. We hypothesized that gilts from a male-biased litter would have a longer AGD and poorer reproductive performance. In Exp. 1, AGD and weight were measured at day 1, day 21, and week 16 of age for gilts from male-biased litters (≥60% males; n = 51) and female-biased litters (≥60% females; n = 51). Sow AGD was measured 3 d after farrowing. In Exp. 2, AGD was measured at gilt selection at approximately 24 wk of age and gilts followed to second parity. Litter sex ratio affected AGD at 16 wk of age, with gilts from female-biased litters having longer AGD (mean ± SEM, 9.1 ± 0.7 mm vs. 11.0 ± 0.6 mm, P = 0.013). Anogenital distance was not different on day 1 or day 21. There was no effect of sex ratio on weight at any time, and sow AGD was not associated with the sex ratio of her litter. Gilts with an AGD longer than the mean of 11.55 mm were heavier (mean ± SEM, 118.8 ± 0.4 kg vs. 117.7 ± 0.4 kg, P = 0.023), were achieved puberty earlier (179.6 ± 0.6d vs. 182.2 ± 0.6 d, P = 0.001), were mated younger (200.6 ± 0.6 d vs. 203.2 ± 0.6 d, P = 0.001), and were more likely to be mated (91% vs. 83%, P = 0.005) than gilts with an AGD shorter than the mean. Gilts with an AGD greater than 11.55 mm had a greater born alive litter size (11.79 ± 0.20 vs. 11.20 ± 0.19, P = 0.018) compared with gilts with an AGD shorter than 11.55 mm. At 16 wk, AGD was associated with sex bias and could be used as a selection tool to predict reproductive success of the first parity, with a longer AGD being associated with gilts that had been born into a female-biased litter and that had better reproductive performance.

Gilt Management for Fertility and Longevity

“…Drickamer et al [38] reported that gilts originating from a male-biased litter (>67% males) had a larger anogenital distance when measured within four days after birth as compared with gilts from litters with lower proportions of males in the litter. In contrast, Seyfeng et al [36] reported that although anogenital distance was not different between male-biased (>60% males) as compared with female-biased (>60% females) litters at day one of age, gilts from female-biased litters had a longer anogenital distance at three and 16 weeks of age. In a second study by the same authors, anogenital distance was measured at the time of preselection at approximately 170 days of age.…”

“…The sex ratio of the litter where the replacement female was born may affect lifetime performance and behavior and could potentially be used as another selection tool at birth [34,35]. Gilts born to litters with a high proportion of males are exposed to increased levels of androgens from their male littermates in utero causing gilts to become masculinized [34,36]. It is generally reported that gilts born in female-biased litters are potentially better replacement females than gilts from male-biased litters, however, more research in this area is needed [34].…”

“…Conversely, Drickamer et al [38] reported that females from litters with a male-biased sex ratio attained puberty later. Nevertheless, further studies reported that gilts from male-biased litters were more likely to have lower successful inseminations, higher insemination failures, lower mating success, fewer pigs born, and less teats as compared with gilts from female-biased litters [35,36,38,39]. Masculinized females from male-biased litters are also more likely to display male-like behaviors, are less likely to be fearful, and more likely to be aggressive than gilts from female-biased litters [40].…”

“…Anogenital distance can be used as an indicator of female masculinization in pigs [36,38]. Drickamer et al [38] reported that gilts originating from a male-biased litter (>67% males) had a larger anogenital distance when measured within four days after birth as compared with gilts from litters with lower proportions of males in the litter.…”

“…In a second study by the same authors, anogenital distance was measured at the time of preselection at approximately 170 days of age. Gilts with an anogenital distance longer than 11.55 mm, and likely from a female-biased litter, were heavier, achieved puberty earlier, were mated younger, and had greater born alive litter size at parity one than gilts with an anogenital distance shorter than 11.55 mm [36].…”