Laura Sala Ayala

Background PGF 2α is commonly given at the end of embryo flushing (EF) to shorten the interval to the next oestrus and ovulation. Objectives To 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 PGF 2α . Study design Controlled experiments. Methods Nine 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). PGF 2α 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. Results The 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 limitations The mare population was limited to barren and maiden mares. The cycle order and operator allocation to each EF were not randomised. Conclusions EF 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 PGF 2α was unaffected; however, there is a considerable risk of unwanted pregnancy (5/27 = 18.5%) in donors from which an embryo was not recovered.