LH and FSH secretion, follicle development and oestradiol in sows ovulating or failing to ovulate in an intermittent suckling regimen.

The present paper describes LH and FSH secretion, follicle development and ovulation in sows that were subjected to a limited nursing regimen. From Day 14 of lactation, 32 sows were separated from their piglets for 12 h every day (intermittent suckling; IS). Half the sows had boar contact during separation. Nine of 32 sows ovulated spontaneously within 14 days from initiation of IS. The frequency of LH pulses on the first day of IS tended to be higher in anovulatory sows (6.3 v. 4.2 pulses per 12 h; P < 0.10); other characteristics of LH secretion were similar to sows that ovulated. The characteristics of FSH secretion did not differ over the 8-h sampling period. Boar contact did not influence either LH and FSH secretion or the number of sows that ovulated. Up to 58% of anovulatory sows showed an increase in follicle size after initiation of IS and, 4 days after the initiation of IS, one-third still had follicles similar in size to those in ovulatory sows. However, the oestradiol concentration in anovulatory sows did not increase. We conclude that FSH and LH stimulation in anovulatory sows is not limiting for normal follicle development, but that ovarian follicles are not responsive to increased LH secretion.