Factors affecting the age at onset of puberty, ovulation rate and time of ovulation in Chinese Meishan gilts

Abstract

Experiments were carried out to study the effects of season on age at puberty, the influence of reproductive age on ovulation rate, and the time interval from the onset of oestrus to ovulation in Chinese Meishan gilts. Gilts approaching puberty either in the spring (n = 88) or in the autumn (n = 40) were housed indoors under natural daylight conditions and observed daily for oestrous behaviour. Gilts approaching puberty in the spring were younger (P < 0.001) and more likely to reach puberty by 100 days of age (P < 0.01) than were those approaching puberty in the autumn. Ovulation rate was estimated in gilts at second (n = 22), third (n = 24), fourth (n = 18), fifth to ninth (n = 9) and tenth to twenty-first (n = 17) oestrous cycle and in primiparous Meishan sows (n = 12) by counting the number of corpora lutea or corpora albicantia at laparoscopy, laparotomy or at ovarian recovery following slaughter. Ovulation rate increased (P < 0.001) with reproductive age and approached that of primiparous sows only when gilts had experienced ≥ 10 oestrous cycles (19.2 versus 21.0). The time interval between the onset of oestrus and ovulation was studied in six naturally cyclic Meishan gilts and nine Meishan gilts administered hCG at the onset of oestrus. All gilts were observed six times a day for the commencement of oestrous behaviour and were subsequently examined by laparoscopy at 32 h following onset of oestrus and every 8 h until ovulation, which was at a maximum of 56 h. Relative to the onset of oestrus, gilts administered hCG ovulated earlier than did the control group (44.2 versus 48.7 h, P < 0.05) and at an interval of 42.2 h relative to the administration of hCG.