Effect of the administration of PGF2 alpha synchronously with insemination on the pregnancy rate in mares in an insemination program

: Investigations in different species including the horse have demonstrated that prostaglandin F2 alpha (PGF2 alpha) is involved in initiating uterine contractions occurring during mating and artificial insemination (A.I.). Uterine contractions play an important role with respect to the sperm transport within the female genital tract. The objective of the present investigation was to evaluate whether the administration of PGF2 alpha (Dinoprost) synchronously to A.I. could have a positive effect on the pregnancy rate in mares. A field study including 346 warmblood-mares (age two to 20 years) belonging to a private studfarm was conducted during the breeding season 1996. The mares were assigned to two groups, group A: mares with spontaneous ovulation, group B: mares in which the ovulation was induced by a GnRH-analog-implant (Deslorelin). PGF2 alpha (Dinoprost) was administered either intramusculary (i.m., 5.0 mg) or intrauterine (i.ut., 0.5 mg diluted in 1.9 ml isotonic NaCl-solution and added to the semen dosis). The study was carried out in a double-blind fashion using isotonic NaCl-solution as a placebo. The mares of each group were randomly assigned to one of the two treatments (i.m. vs. i.ut.). The following first cycle pregnancy rates (day 18) were obtained in mares treated and inseminated once per oestrus: group A1 (PGF2 alpha, i.m.): 54.5% (n = 33); group A2 (placebo, i.m.): 69.7% (n = 33); group A3 (PGF2 alpha, i.ut.): 65.4% (n = 26); group A4 (placebo, i.ut.): 69.8% (n = 32); group B1 (PGF2 alpha, i.m.): 56.5% (n = 46); group B2 (placebo, i.m.): 29.6% (n = 27); group B3 (PGF2 alpha, i.ut.): 66.7% (n = 45); group B4 (placebo, i.ut.): 60.0% (n = 30). The pregnancy rates did not differ between the different groups with the exception of group B2 (p < 0.05). In mares treated repeatedly during the oestrus period (group A, n = 88; group B, n = 23), the pregnancy rates did not differ significantly between treatment and control groups. From the results obtained it is concluded that the PGF2 alpha-application did not show an effect on the pregnancy rate. Further factors influencing the results to a small degree were the stallions, semen age and quality and frequency of insemination per oestrus.