Effect of placental retention time and associated treatments on reproductive performance in heavy draft horses

Abstract

The effect of placental retention time on reproductive performance was investigated in several heavy draft breeds of horses. The study was based on a total of 422 mares varying from four to 20 years in age, which had foaled during the period 1991 to 1994. The placental retention time for this group of mares ranged from a minimum of 119 minutes to a maximum of 183 minutes with a mean of 148 minutes. A decrease in pregnancy rate followed on breeding at the foaling heat in mares that had a placental retention time greater than one hour. Mares with a placental retention time of less than one hour or longer than four hours had pregnancy rates of 66% and 51.7%, respectively, when bred on their foaling heat. Manual removal of a retained placenta was subsequently associated with reduced reproductive performance in those mares. Mares with a placental retention time of less than four hours and which had received oxytocin treatment, had a pregnancy rate at foaling heat of greater than 70%. Where oxytocin treatment was delayed, on the other hand, the number of days from parturition to last breeding data was correspondingly increased. Aerobic bacteria were cultured from the uterus in 47.2% and 100% of mares whose placental retention times were less than eight hours or greater than eight hours, respectively. The subsequent reproductive performance of mares with a placental retention time of greater than four hours was improved if the uterus was irrigated. The findings of this study indicate that rapid administration of oxytocin administered at a dosage 50 IU is the best treatment for retained placenta and the application of intrauterine treatments such as uterine irrigation in prolonged cases of placental retention is likely to improve subsequent breeding efficiency.