Relationships between age at puberty and interval from weaning to estrus and between estrus signs at puberty and after the first weaning in pigs.

The study comprises observations in 464 Swedish Yorkshire pigs at puberty and after the first weaning. The aim was to study relationships between age at puberty and weaning to estrus interval and between estrus signs at puberty and after the first weaning. The estrus signs were checked, and blood samples for progesterone determination were drawn regularly around puberty and after the first weaning. Gilts expressing early puberty (youngest one-third) showed a greater ability to return to estrus and to ovulate within 10 d after weaning than gilts expressing late puberty (oldest one-third) (P = .01). A positive genetic correlation was found between age at puberty and the interval from weaning to the first detected estrus (WEI) (rg = .45). The genetic correlation between age at puberty and the ability to show the standing reflex and to ovulate within 10 d after weaning was negative (rg = -.50). The heritability of the ability to show the standing reflex and to ovulate within 10 d after weaning was .31. Gilts not showing a standing reflex at puberty also had a higher incidence of ovulation without a standing reflex within 10 days after their first weaning (21.4 vs 6.2%, P = .001). There was a significant positive correlation between the total duration and the intensity of the reddening and swelling of the vulva at puberty and after the first weaning. This study demonstrates relationships both between age at puberty and WEI and between some estrus signs at puberty and after the first weaning.