Breed For Success

By Toni McAllister

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Three equine reproduction centers explain their methodologies.

Technological advances in equine reproduction continue to open doors for equine practitioners.

Breeding today seems to be more science than nature, and having the right tools and skills to ensure a successful pregnancy is paramount.

Discussions with three leading equine reproduction centers about the processing and handling of cooled and frozen semen, as well as the equipment and processes used for handling embryos intended for transfer, conveyed a consistent message: quality control counts.

Select Breeders Services

Founded in Maryland in 1987, Select Breeders Services (SBS) has expanded to become an organization with affiliates that offer semen freezing and related equine reproductive services throughout the U.S., Europe and Australasia.

Whit Byers, M.S., who partnered with SBS founder Paul Loomis in 1992, owns SBS Southwest in Aubrey, Texas, which has become the largest semen-processing laboratory in the SBS network. The facility stores nearly 25,000 doses of frozen equine semen from more than 600 stallions.

The key to SBS’s success has been its quality-control commitment. “We do everything we can,” Byers says.

The USDA previewed plans for SBS Southwest and consequently inspected and approved the facility for international semen export.
About 60 percent of SBS Southwest’s business is referral, including veterinary-referred equine semen analysis, pre-purchase semen analysis, management practices for young and problem stallions and customized semen freezing protocols. The facility also processes cooled semen and stands stallions.

In the U.S., there is no certification system to guarantee the viability of shipped semen. “If semen from a (virile) stallion is processed correctly, then it works out quite well,” Byers explains. “But the problems come in when the stallion isn’t as fertile and processing mistakes are made.”

The semen processing and handling controls at SBS Southwest are stringent. After a stallion has been properly cleaned, one or more test freezes are done to allow a customized freezing protocol. The protocols differ in the centrifugation and freezing extenders used and the cooling rates employed.

“I would encourage anyone who is handling semen for breeding to read up on the technological advances that have come along,” Byers says. “Processing techniques have come a long way to enhance what we’re doing.”

For example, he says, centrifugation of semen has increased in use and is a “very effective management tool for processing stallion semen.” These advances include cushioned semen centrifugation and centrifugation speed to enhance semen viability.

Regardless of the protocol used, the basic elements are the same: Immediately following collection, a small semen sample is analyzed to determine sperm concentration and quality using computer-assisted analyzers. The semen is diluted and centrifuged to remove the majority of the seminal plasma, and the sperm pellet is resuspended in an extender that contains ingredients to protect the sperm during the freezing and eventual thawing processes.

As a quality-control measure, all extenders used at SBS labs are manufactured at the SBS lab in Maryland.

“Again, it’s a quality-control issue,” Byers says. “It gives our clients a level of assurance to ensure semen quality is the best it can be.”

Once extended, sperm are loaded into 0.5 ml plastic straws. Each stallion’s straws are preprinted and marked with the stallion’s name and registration number as well as the year frozen, lot number, location of the freezing site and USDA lab number. Once all the semen is loaded, the straws are placed in a controlled rate cell freezer. After the semen has completed the freezing process, it’s immersed and maintained in liquid nitrogen in cryogenic containers.

Byers says semen viability is a tricky business. About 20 percent of the stallion population is virile while the bottom 10 percent are not candidates for semen freezing. It’s the middle population that’s most troublesome, he says.

“The middle ground may require special processing—different extenders, change the freezing curves and/or antibiotic levels,” Byers says. “Sometimes it’s a problem with the stallion, but sometimes it’s a processor problem.”

Equine Reproductive Veterinary Services

Jorge L. Colón, DVM, heads Equine Reproductive Veterinary Services (ERVS), a Lexington, Ky., facility dedicated to equine embryo transfer.

Dr. Colón can attest to the need for quality semen processing. ERVS doesn’t manage stallions on site, so all semen is transported to his facility.

“It’s out of my control. I get what I get,” Colón says.

If the semen comes from a reputable facility, then quality is usually good, but new breeders often make mistakes. “Many don’t send a whole dose, or there’s a quality control problem,” Colón says.

When semen quality is high, ERVS thrives.

“The goal here is to ensure quality pregnancies,” Colón explains, noting that quality is emphasized over quantity.

The expected pregnancy success rate at ERVS is about 80 percent or better at 14 days, with about a 10 percent rate of pregnancy loss after that time. Colón says ERVS’s success rate at 26 days (when a heartbeat is present) is 78 percent, and he attributes the high success to his ability to control many factors.

For example, donor mares are typically managed on site, and ERVS maintains a healthy herd of recipient mares on site as well.

“We take care of the recipient mares in a non-stressful manner,” Colón explains, which he says is critical to pregnancy success. “Ensuring our recipient mares are non-stressed, healthy and well-cared for is one of the most important things we do here.”

Embryo harvesting is most often done on site. Equine embryos migrate into the uterus on day 5 1⁄2 or six post ovulation. At ERVS, the optimal time for embryo recovery is day seven or eight post ovulation (day six recovery is performed for embryos that will be vitrified). Trans-cervical uterine flushing of the donor mare is performed and the fluid is removed and passed through a filter. The filter cup is analyzed for embryos under a stereomicroscope. Any recovered embryo is washed,  analyzed and graded for quality.

Healthy embryos are collected into holding straws to await packaging for transport or transfer into a recipient mare. Trans-cervical uterine deposition of the embryo is performed into a suitable recipient mare. The recipient mare is examined via transrectal ultrasound at 14 days of embryo age for uterine evaluation and confirmation of pregnancy.

Colón says ERVS monitors the embryo’s growth and is not satisfied with the true establishment of a viable pregnancy until a foal heartbeat is confirmed.

“You need to be very good at manipulating the embryo into the straw,” Colón says, noting that people working in embryo transfer have a great responsibility. “We have the potential of damaging that embryo,” which potentially means a failed pregnancy or unhealthy foal.

Royal Vista Southwest

Since 2000, Royal Vista Southwest of Purcell, Okla., has concentrated on equine reproduction and at press time had completed its eighth breeding season. The facility has a nationally respected embryo-transfer program  boasting “better than 80 percent early pregnancy success and 75 percent success at 25 days” (viable heartbeat) for both shipped and on site embryo transfers.

Like ERVS, Royal Vista Southwest doesn’t maintain stallions on site and instead focuses on mares. Screened for reproductive soundness, well-fed and maintained under a preventive medicine program, recipient mares are the pride of Royal Vista Southwest’s transfer program.

“We maintain a herd of 825 recipient mares,” says James W. Bailey, DVM, a partner at Royal Vista Southwest. Such a large herd ensures there are enough recipient mares synchronized to each donor mare.

The embryo-transfer process  includes monitoring the donor mare with daily ultrasounds to establish the ovulation date and simultaneously monitoring recipient mares to look for matching cycles.

“We like to flush mares at seven days (after ovlulation),” Dr. Bailey says. “Six-day flushes are just as successful, and some people do eight-day flushes, but we find these embryos too fragile. At nine days, the embryos are very difficult to handle.”

As soon as the embryo is found, it’s processed and transferred into a waiting recipient mare.

Royal Vista Southwest does utilize embryos harvested offsite as well. These embryos are packaged for cooling and shipping for same-day delivery. Upon arrival at Royal Southwest, the embryo is transferred into a recipient mare.

The company also performs embryo vitrification. To prepare an embryo for vitrification, it is harvested as usual, then suspended among high concentrations of cryoprotectants in liquid nitrogen.

Bailey says the pregnancy rate is 70 to 75 percent per embryo transferred after vitrification.

Quality control of the cryoprotectants is crucial.

“We’re very particular about what we use and how it’s stored,” Bailey says.

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