Plasma prolactin in relation to changes in oestrous cyclicity following olfactory bulbectomy in post-pubertal pigs

Prolactin was determined by radioimmunoassay in the peripheral plasma of five post-pubertal Large White gilts before and after olfactory bulbectomy. In the oestrous cycle before bulbectomy and in cycles after bulbectomy, the highest concentrations of prolactin were found during the period from the late luteal phase to oestrus. Throughout the prolonged summer anoestrus which occurred after bulbectomy, the amounts of prolactin were similar to base-line quantities found during the oestrous cycle between Days 3 and 12. These results differ from those found for the seasonally breeding European wild sow where high prolactin levels are associated with a summer anoestrus.