Endocrinology of parturition in the pig

Abstract

Endocrine and physiological events that precede and accompany parturition in the sow occur in a sequential fashion starting with a slow increase in estrogens from about three weeks prior to parturition. The luteotrophic role of LH visible as a distinct LH-progesterone relation is present at three weeks prior to parturition but can no longer be seen at one to two days prior to expulsion. Progesterone has not completed its decline during expulsion. A rather sharp and transient increase in plasma relaxin is known at about one day prior to expulsion. Corticosteroids are elevated also during the last 24 hours before parturition with a peak during expulsion. Oxytocin levels remain at baseline levels till progesterone has reached values below 10 ng/ml when a two step sharp increase in plasma oxytocin can be observed; one step prior to expulsion and a second during expulsion. Concomitant to endocrine changes the uterine EMG displays characteristic patterns, but is insensitive to oxytocin four days prior to parturition.