AAEP Convention 2005: Increasing Embryo Recovery and Fertility

In a study from the University of Saskatchewan, Canadian researchers compared ovulation rates, embryo recovery and quality, and subsequent pregnancy rate using two estrus synchronization methods--prostaglandin (PG) administration and progesterone and estradiol (PE) administration--both combined with equine follicle-stimulating hormone (eFSH) treatments. Tal Raz, DVM, presented the researchers' findings at the 51st Annual American Association of Equine Practitioners Convention, held in Seattle, Wash., Dec. 3-7, 2005.

Embryo transfer allows owners to maximize the number of foals from a particular mare, and can be useful when it is not desirable or possible for a mare to carry a foal full term.

Single embryo recovery attempts are common in equine embryo transfer and on average resulted in a 50% recovery rate. Recovering embryos from multiple ovulations or superovulation is less common because superovulating mares is problematic. Equine pituitary extract has been used to stimulate multiple ovulations in mares, but is not commercially available. Previous studies have shown a purified pituitary extract product called eFSH has been successful in donor mares, but little information is available on the combined use of eFSH with estrus synchronization protocols in terms of time to ovulation, embryo recovery, and post-transfer pregnancy rates.

During embryo transfer, donor and recipient mare ovulations need to be closely aligned to optimize survival of the transferred embryo in the recipient. The close alignment in ovulation is required because the recipient mare's uterus has to be at the right stage to receive the donor's embryo. Raz's study focused on the process of getting donor mares ready for breeding and ovulation, in hopes of finding a method that was reliable, predictable, and cost effective.

Prostaglandins are the most commonly used hormonal therapy in the horse industry, according to Raz. "Prostaglandin and its analogs, when administered exogenously, are valuable tools for inducing regression of the corpus luteum (progesterone-secreting endocrine tissue that forms immediately after ovulation) and subsequent return to estrus.

Researchers used 12 mares in 2 estrus cycles and each mare received both treatments. "We found few statistical differences between (PE and PG) treatments. The mean number of ovulations tended to be higher in the PG-treated group (30 per group compared to 15 per group in the PE-treated group)," Raz reported. However, pregnancy rates for the two groups were not significantly different nor were the embryo recovery rates (PE: 1.0; PG: 1.4 embryos per mare).

And "while there were fewer ovulations, more embryos developed from the progesterone- and estradiol-treated mares (45.5%) compared to the prostaglandin-treated mares (26.7%)," but these differences were not statistically different he went on.

Both PE and PG treatments are commonly used for equine embryo transfer. However, the commercially available PG treatments are generally less expensive than PE because PE is only available through compounding pharmacies. The PE treatment may be started at any stage of the estrus cycle. Raz noted that the PE protocol is more predictable and reliable than PG treatments in terms of synchronizing estrus and ovulation, but PE treatment requires daily handling of the mare for treatment. Prostaglandin is less predictable in terms of time to ovulation and it requires more monitoring of the mare. If PE is used in both donor and recipient mares at the same time, only one recipient is usually used. If PG is used, 2 recipient mares are synchronized for each donor mare because the response is more variable. Maintenance of recipient mares is one of the highest costs in embryo transfer, so if fewer are used for each donor, the cost is lower per procedure. "Embryo transfer has increased steadily over the past two decades," Raz said. "Economically, there is a need to increase the success rate of embryo transfer," and using PE protocols might be a way to reduce costs associated with the procedure.

About the Author

Chad Mendell

Chad Mendell is the former Managing Editor for TheHorse.com .

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