Changes in oestrous cyclicity following olfactory bulbectomy in post-pubertal pigs.

Bilateral olfactory bulbectomy was carried out on 16 post-pubertal gilts during the winter and spring of 2 consecutive years. Eight bulbectomized gilts in Exp. 1 had 2-7 regular periods of oestrus before becoming anoestrous for greater than 100 days in the summer and autumn. During November, 3 of these gilts were placed with b boar and became oestrous within 9 days, were mated and established normal pregnancies; the remaining pigs also resumed normal oestrous cycles when transferred to other pens. The following year anoestrus again occurred during the summer in gilts and in sows after weaning. In Exp. 2, 8 bulbectomized gilts remained in the same pens throughout the experiment, 4 were housed with a vasectomized boar and 4 away from boars. As in Exp. 1, the same periods of anoestrus occurred throughout the year, whereas 4 unoperated pigs housed nearby had continuous oestrous cycles. Ovulation without oestrus occurred in some bulbectomized pigs even after gonadotrophin treatment. Prolonged anoestrus in Exp. 1 was associated with non-ovulatory levels of plasma oestrogen and low plasma progesterone and LH values. Behavioural, morphological and endocrine data indicate that the effects of bulbectomy on oestrous cycles in post-pubertal gilts are mediated at the hypothalamus. The seasonality of the effects seems likely to be due to bulbectomy unmasking a photoperiodic influence.