Effects of repeated embryo flushing without PGF_2α administration on luteal function, percentage of unwanted pregnancy and subsequent fertility in mares

Abstract

BackgroundPGF2α is commonly given at the end of embryo flushing (EF) to shorten the interval to the next oestrus and ovulation.ObjectivesTo determine the effect of repeated EF on plasma progesterone concentration, percentage of mares with endometritis, unwanted pregnancy and subsequent fertility in mares flushed without the use of PGF2α.Study designControlled experiments.MethodsNine mares were inseminated in seven consecutive cycles (n = 63), to either perform an EF (n = 54) 7–9 days after ovulation or left pregnant (n = 9). PGF2α was not used to induce oestrus. Ultrasound examination and blood sampling were performed just before the EF and 72 h later to determine changes in progesterone concentration and signs of endometritis.ResultsThe overall percentage of positive EF/pregnancy was 55.5% (30/54) and 66.7% (6/9), respectively. The likelihood of pregnancy/positive EF in the first three cycles was 55.5% (15/29). This was not different (p > 0.1) from the fertility of the last four cycles (69.4%, 25/36). In five EF cycles (9.3%), mares had signs of endometritis and early luteolysis (progesterone <2 ng/mL) 72 h after EF. The reduction in progesterone concentration by 72 h after EF was greater (p < 0.05) for Day 9 (−2.3 ± 0.7 ng/mL) than Day 7 (−1.0 ± 0.8 ng/mL) or Day 8 (−1.3 ± 1.1 ng/mL) cycles. The progesterone concentration in non‐flushed mares did not vary significantly during the sampled period (Day 7–12). There were 5 cycles in which the donor mare remained pregnant after the EF, although four were from a single mare.Main limitationsThe mare population was limited to barren and maiden mares. The cycle order and operator allocation to each EF were not randomised.ConclusionsEF induces a subtle, but significant reduction in progesterone concentrations compared with non‐EF cycles. However, the percentage of mares with EF‐induced full luteolysis is low (9.3%). The fertility of mares after repeated EF without administration of PGF2α was unaffected; however, there is a considerable risk of unwanted pregnancy (5/27 = 18.5%) in donors from which an embryo was not recovered.

Pregnancy and Luteal Responses to Embryo Reinsertion Following Embryo Flushing in Donor Mares

“…20 to 22 days), equivalent to that from recipient mares receiving an embryo observed in the current and previous studies [27]. Cervical and uterine manipulation during embryo flushing per se do not appear to cause enough oxytocin and prostaglandin release to induce full luteolysis and return to oestrus [1,12,28] to explain embryo loss due to luteal insufficiency after embryo reinsertion. In fact, several unwanted pregnancies have been reported following a negative flushing in embryo donor mares in which the embryo was left into the uterus at the time of flushing [9,12].…”

“…Cervical and uterine manipulation during embryo flushing per se do not appear to cause enough oxytocin and prostaglandin release to induce full luteolysis and return to oestrus [1,12,28] to explain embryo loss due to luteal insufficiency after embryo reinsertion. In fact, several unwanted pregnancies have been reported following a negative flushing in embryo donor mares in which the embryo was left into the uterus at the time of flushing [9,12]. However, whether subtle and transient inflammation caused during uterine lavage could affect embryo development and survival without inducing luteolysis is unknown.…”

“…A drop of the aliquot was plated in blood agar (BD Columbia agar, 5% sheep blood, Becton Dickinson Gmbh, Heilderberg, Germany) and incubated for 24 h at 37 C for bacteriological culture and identification. Bacterial growth and morphology and the presence of haemolysis around bacterial colonies were evaluated macroscopically 24 h after incubation, as described previously in our laboratory [12].…”

“…Several studies [9][10][11] have shown the possible outcome of pregnancy establishment following unsuccessful embryo flushing (negative embryo recovery). The likelihood of unwanted pregnancy following a negative embryo flushing can be significant (around 20%) when PGF2α is not administered following embryo flushing [12], which contrasts with the difficulty of reinstating a pregnancy after embryo flushing and reinsertion [1,2].…”

“…It is unknown whether reinserted embryos fail due to PGF2α release and endometrial inflammation from the uterine lavage procedure or accidental bacterial contamination during embryo transfer. On the other hand, full luteolysis and reduction in progesterone concentration to basal levels does not appear to be a cause of embryo failure following embryo reinsertion, since most mares maintain the CL and even show prolonged dioestrus following embryo flushing [1,[12][13][14].…”