Effects of embryo flushing on serum progesterone levels and the inter-ovulatory period in Arabian donor mares

Abstract

To obtain the maximum number of cycles throughout the breeding season, avoid unwanted pregnancies and possible endometritis, the luteal phase of donor mares is shortened after embryo flushing. This is achieved by treating the donor with prostaglandin F2α (PGF2α) to destroy the corpus luteum and hence shorten the inter-ovulatory interval (IOI). It has been suggested that manipulation of the cervix and/or uterus during embryo flushing may result in release of endogenous of PGF2α and/or oxytocin, resulting in altered luteal function with a consequent decrease in progesterone and shortening of the cycle. Conversely, other authors have proposed no change in or extension of cycle length following embryo flushing. The purpose of this study was to evaluate the effects of embryo flushing with or without administration of PGF2α on serum progesterone levels and inter-ovulatory interval (IOI). Over two breeding seasons, 26 cycles of 6 Arabian donor mares, aged 4-15 years were studied. Inseminated mares were flushed on Day 8 or 9 post ovulation using Ringer's Lactate and a standard closed embryo flushing technique. After flushing the mares were divided into 2 groups; Group 1 (n=9) were treated with dl-Cloprostenol and Group 2 (n=17) were untreated. Blood wascollected on the day of embryo flushing and 48h later and the serum frozen until analysis using a progesterone ELISA kit (DRG Instruments, Marburg, Germany). For statistical analysis, a Shapiro-Wilks normality test was performed before 2-way ANOVA, followed by Tukey's post hoc and unpaired T tests. A significant decrease in plasma progesterone concentrations was observed in Group 1 mares (12.08 ± 3.91 ng/ml at flushing vs 0.7 ± 0.28 ng/ml at 48h, p<0.001) but not in Group 2 (12.62 ± 4.76 ng/ml at flushing vs 10.89 ± 3.57 ng/ml at 48h, p=0.549). The inter-ovulatory interval was shorter in Group 1 compared to Group 2 mares (18.56 ± 1.94 vs. 20.94 ± 1.84 days, respectively; p=0.006). Only 2 cycles had follicles ≥28mm at the time of embryo flushing and PGF2α was not administered in those cycles. Although the IOI was shortened by a mean of 2.38 days in mares given PGF2α, this was less than the 5-6 days which the dioestrous phase of the cycle had been shortened by. Based on the results obtained in this study, manipulation of the reproductive tract during embryo flushing does not result in endogenous release of PGF2α and/or oxytocin that is sufficient to cause luteolysis of the CL or cause a significant decrease in serum progesterone levels in embryo donor mares.