Lack of effect of clenbuterol for delaying parturition in late pregnant mares

摘要

Parturition in mares occurs mainly at night and a special surveillance is necessary for pregnant mares near term. Although, the calcium concentration in mammary secretions may help to indicate the last few days of pregnancy, they are not so reliable that they can predict the exact date of birth [ 1,2]. Moreover, due to the late maturation of the foetal foal, induction of parturition should be avoided because of the risks of producing a premature foal. In cattle and in man, tocolytics are used to delay parturition in physiological and pathological conditions. In mares at risk of premature parturition, the tocolytic drug clenbuterol has been administered twice daily at a dosage of 0.8 #mu#g/kg [3]. Administration of 300 #mu#g of this #beta#2 adrenergic agonist has also been shown to decrease uterine tone in pregnant mares throughout pregnancy for at least 2 h and to decrease fetal heart rate just after treatment [4]. The aim of this study was to test the efficacy of repeated clenbuterol treatments in delaying parturition in mares at term.