Use of serial progesterone measurements to assess cycle length, time of ovulation and timing of uterine flushes in order to recover equine morulae

Abstract

In 1987, as part of an embryo transfer programme to produce monozygotic twin foals, mares were flushed during the morning (09:30 to 13:30 h) of Day 6. Of 100 flushes, 48 embryos were recovered half of which were morulae. In 1988, in an attempt to increase the proportion of morulae, various flushing times between 17.00 h on Day 5 and the afternoon of Day 6 were used. For flushes carried out during the morning of Day 6, recovery rates were similar to those of the previous year. However, although the proportion of flushes resulting in the recovery of morulae was not significantly different for times between 23:00 h on Day 5 and 13:00 h on Day 6, the overall recovery rates for flushes on Day 6 were higher than those on Day 5. In addition, a number of mares that did not produce an embryo when flushed before 09:00 h on Day 6, were subsequently found to be pregnant when scanned at Day 18 suggesting that flushing had been carried out before arrival of the embryo in the uterus. To determine whether valid predictions could be made as to when to flush a mare to maximise recovery of morulae, a review of embryo recovery rates and plasma progesterone profiles of a large herd of mares over two breeding seasons was carried out. Mean plasma progesterone levels on the first three days after ovulation were higher for mares that produced embryos when flushed on Day 5 than for all other groups. Comparison of the results of previous flushes with the corresponding plasma progesterone profiles suggested that the characteristics of the post ovulation progesterone rise may have some value in deciding when a mare should be flushed. A review of the effects of uterine flushing, PGF2α and hCG on cycle length and ovulation time was also carried out in order to devise more efficient methods of herd management and ensure a supply of suitably synchronised recipient and donor mares at convenient times for embryo transfer experiments.