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

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Abstract
Bilateral olfactory bulbectomy was carried out on 16 post-pubertal gilts during the winter and spring of 2 consecutive years. Eight bulbectomized gilts in experiment 1 had 2-7 regular periods of estrus before becoming anestrous for > 100 days in the summer and autumn. During Nov., 3 of these gilts were placed with a boar and became estrous within 9 days, were mated and established normal pregnancies; the remaining pigs also resumed normal estrous cycles when transferred to other pens. The following year anestrus again occurred during the summer in gilts and in sows after weaning. In experiment 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 experiment 1, the same periods of anestrus occurred throughout the year, while 4 unoperated pigs housed nearby had continuous estrous cycles. Ovulation without estrus occurred in some bulbectomized pigs even after gonadotropin treatment. Prolonged anestrus in experiment 1 was associated with non-ovulatory levels of plasma estrogen as well as low plasma progesterone and LH [luteinizing hormone] values. Behavioal, morphological and endocrine data indicate that the effects of bulbectomy on estrous cycles in post-pubertal gilts are mediated at the hypothalamus. The seasonality of the effects may be due to bulbectomy unmasking a photoperiodic influence.