Effect of administration of phenylephrine immediately after low dose insemination on pregnancy rates in mares

Abstract

There is considerable pressure on equine veterinarians to achieve good pregnancy rates with very small doses of semen. Phenylephrine administration in the rabbit increased numbers of oviductal, uterine, and cervical sperm, myometrial contractions, and fertilized ova after low dose insemination. The use of phenylephrine to enhance uterine contractility and fertility has not been investigated in the mare. Thus, the objective of this study was to determine if phenylephrine administration would result in clinically acceptable pregnancy rates in mares bred by low dose insemination. The hypothesis (Ha) was that pregnancy rates would be significantly higher in mares receiving phenylephrine compared to saline controls. Six pony mares and eight horse mares were enrolled in this study. Mares were inseminated within 24 hours of ovulation with 30 million progressively motile spermatozoa from a single fertile stallion. Immediately following insemination, mares were administered either phenylephrine (0.06 mg/kg) or 1mL of saline via IV injection. Pregnancy status was determined 14 days following ovulation via transrectal ultrasonography. Pregnancy rates in phenylephrine treated mares were 44% (4/9) while 22% (2/9) in saline-treated mares (P > 0.05).