Cover Story | Reproduction

Stop Being a ‘Pajama Vet’

By Marie Rosenthal MS

Jutta Sielhorst, DMV, DECAR, used to be a “pajama vet” during breeding season, waking up periodically during the night to scan the mare to find the best time to artificially inseminate (AI) her.

Then a New Zealand veterinarian showed her another way: “You German pajama vets, you should stop getting up at night,” Dr. David Hanlon told her. “It’s so dangerous, and what you are doing is not physiologically [sound].”

It took a little convincing, she admitted at the BEVA Congress, held in September in Liverpool, England, but she and her staff are getting a good night’s sleep.

“Our aim is to inseminate close to ovulation to get a good chance of fertilization,” she said, and that success depends on many things, including the availability and viability of the stallion’s sperm, the mare’s health and condition, and timing the ovulation. The optimal time for induction of ovulation and breeding depends on the mare’s breed, age, body condition score, reproductive history, the season, the number of days a mare is in estrus and the interval from prostaglandin administration, Dr. Sielhorst explained.

“Stallion fertility plays a role, and the semen quality in the straw plays a role, but also the mare plays a role. If we have a problem mare, we might feel more secure if we can inseminate her several times,” she said. Since that is more difficult today, the question becomes: Can we trust the mare to ovulate when we expect it? The answer, it turns out, is usually, the number of straws that reproductive veterinarians had to work with also improved success, but the cost has lessened the number over the years, and frequently all they have is 1 straw, making the timing even more important.

No where is the adage, “Timing is everything,” truer than during equine breeding season.

The traditional practice is to scan the mare every 4 to 6 hours and inseminate around 6 hours after ovulation. At night, one might increase the scan intervals to closer to 6 hours and inseminate within 6 to 15 hours after ovulation.

Some might use a fixed-time AI with an entire semen dose. Some might use ovulation-inducing drugs and then inseminate 33 to 36 hours after ovulation induction. If there are 2 straws of semen—a luxury these days—they might inseminate 30 hours after ovulation and then a second time, 40 hours after ovulation.

In a quick survey done during her lecture, 46% of the attendees would scan the mare every 4 to 6 hours and do the AI within 6 hours after ovulation. This timing has good data behind it: In the early 90s, Woods, et al., found if mares were checked every 4 to 6 hours, the pregnancy rates were high, and pregnancy losses were low (Theriogenology 1991;36[5]:823-30).

A recent study found no significant difference among examination intervals of 4, 8 and 16 hours to detect ovulation, even if they only had 1 straw, according to Dr. Sielhorst (J Equine Vet Sci. 2020;87:102900).

But the study that convinced her to stay in bed was done in New Zealand, which compared the pregnancy-rates data collected from 1996 to 2002 when they scanned the mare every 6 hours and did AI post ovulation and compared these cycles to the protocol used between 2002 and 2017 when they used a fixed-time, AI protocol before ovulation [J Equ Vet Sci 2018, 66:198]. Dr. Hanlon would give them human chorionic gonadotropin (hCG) in the morning and check the next day to see if there was a follicle in case it came early. He did not scan the mare again and would inseminate before he left for the day around 5 to 5:30 pm—about 33 hours past hCG administration. He found 96 mares ovulated within 45 hours.

When he analyzed the different effects of mare age, reproductive status, stallion and insemination, he found a pregnancy rate of 54% pregnancy in the fixed-time AI pre-ovulation and 38% in the ovulation AI, if the mares were given a full insemination dose.

The argument in favor of inseminating the mare before she ovulates is more physiological. There is a sperm reservoir; the oocyte quality still will be good. And if the mare is a problem, she’s under the influence of estrogen longer and has better contractions and an open cervix after the insemination, according to Dr. Sielhorst.

In addition to ovulatory-inducing drugs, teasing behavior is important, as are the degree of cervical relaxation and the uterine edema when you induce ovulation. In addition, the diameter, formation and softness of the follicle provide useful information.

“We know these are the preconditions for successful induction of ovulation. And if we hit this, we have a high chance that the mare will ovulate in the expected window, which will be, depending on the season, around 34 to 36 hours after hCG,” she said.

New ultrasonography can provide more precise images of the follicle, and the concentrated blood flow can be seen with Doppler. “It’s all around the follicle earlier, but close to ovulation, 2 to 4 hours before it’ll concentrate on the base on the opposite side of the apex. And that can also help you to decide whether you can trust this mare will ovulate,” she said.

In nature, the stallion will breed several times with the same mare, which improves pregnancy rates. So, it stands to reason that AI done more than once would be more successful. If you have 2 straws, it might be a good idea to inseminate before and after ovulation.

You can use a split-dose protocol by giving hCG around 8 a.m., then scan the mare again in late afternoon or the next morning, and inseminate the mare about 32 hours post-hCG, and then again, the next morning, at 48 hours post-hCG. With this split-dose protocol, the pregnancy rate is about 50% compared with a post-ovulation protocol of about 33% (Stout TAE, et al. ICERM congress 2020).

With a problem mare, Dr. Sielhorst switches it up a bit. If someone can give a dose of hCG at night, she checks the mare early in the morning, again in the afternoon, and then inseminates the next morning with half a dose. And then she does a fluid check.

“We used to do that 4 to 6 hours after insemination, but we learned from recent work that we can do the flushing earlier. So, we could do it 2 or 3 hours after AI and then clean the mare again, and then have her again inseminated at 5 o’clock in the afternoon,” she suggested.

There are pluses for the veterinarian in not scanning every 6 hours, she said, including better life-work balance and safety. “So, it’s a positive thing, and I hope I’ve convinced you not to be a pajama vet anymore with this study, but of course we need to trust that the mare will ovulate if we inseminate the mare pre-ovulatory,” she said. MeV

Dr. Sielhorst will offer reproduction training seminars on Nov. 28 and 29. Find out more:
https://www.reprotraining.de/en/