The Modern Equine Vet
December 2023
Vol 13 Issue 12 2023
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News Notes

A New Way to ‘Re-Cycle’ Your Mare

By Paul Basilio

When a mare loses a fetus, it can take months to get her back into cycle, thanks to the enduring nature of endometrial cups.

Endometrial cups are crucial, as they produce the hormone equine chorionic gonadotropin (eCG), which sends signals to the ovary to produce secondary corpora lutea (CLs). The CLs produce immense amounts of progesterone, which can sustain the mare’s pregnancy for approximately the first half of gestation.

“Endometrial cups can also be little buggers,” said Carleigh Fedorka, DVM, PhD, assistant professor of equine reproductive physiology at Colorado State.

“When the mare loses the fetus, those endometrial cups persist for their entire lifespan, regardless of embryo or fetal viability.”

That means if the mare loses the pregnancy on day 30, those secondary CLs are still going to be producing lots of progesterone, which will keep the mare from cycling back.

Since up to 10% of pregnancies are lost in the first 60 days, that’s a lot of waiting around for a lot of mares.

“We’ve tried a lot of things to hasten the degradation of these cups,” Dr. Fedorka said during a Burst session at the 69th AAEP Annual Convention in San Diego.

“We’ve tried surgery, ablation and chemical curettage with kerosene with either inconsistent or no success.”

Settle for the Best
The idea of bringing mares back into cycle was put on the backburner until Dr. Fedorka’s friend, theriogenologist Maria Schnobrich, VMD, DACT, called her one day about a mare with retained endometrial cups.

Dr. Schnobrich asked about Settle, a mycobacterium cell wall fraction (MCWF) immunostimulant used to treat equine endometritis caused by Streptococcus zooepidemicus.

Dr. Fedorka initially laughed at the suggestion, but after a little thought it made much more sense.

“Endometrial cups are naturally degraded at 150 days by lymphocytes,” she explained. “We know that Settle can increase the production of a lot of cytokines that recruit the lymphocytes and help develop them into the type of lymphocytes that would be useful.”

She added: “So after laughing at her, I said, ‘Obviously, we need to study this.’”

They then set out to develop a protocol.

DIY Re-Cycling
First and foremost, a video endoscope is needed to visualize the endometrial cups and to inject them individually. Injection needles will be used to penetrate the epithelium of the endometrium and get the treatment into the stroma.

For their protocol, 2 treatments are performed 7 days apart using 4 vials of Settle during each session.

You’re also going to need 3 people: 1 person in the mare, 1 person driving the endoscope, and 1 person injecting the treatment solution.

The treatment solution includes 6 mL of Settle combined with 14 mL of lactated ringers solution.

“You have to visualize each endometrial cup, inject 1 mL of solution, and then find the next cup,” Dr. Fedorka explained.

To test the protocol, her team brought in mares that had aborted at about 45 days’ gestation.

“We brought them in for their hysteroscopy, and we injected the individual cups,” she said. “If we had any treatment solution leftover, we injected it circumferentially around the endometrial cup line. Then we waited 7 days and redid the treatment.”

Results showed consistent, reliably reduced eCG concentrations that were negligible by about day 28. In terms of return to cyclicity, 80% of the treated mares cycled back and came into heat about 24 days after treatment onset.

“We reduced the [return to cyclicity] time by 2 to 3 months,” she added. “We were also lucky to have some incredible theriogenologists take this protocol into the field.”

To date, the protocol has been performed on 17 mares. Of those 17, they have a history about 12.

“Of those 12, nine are currently pregnant and should be foaling in this upcoming season,” she said, adding that “I hope you don’t have a mare lose her pregnancy, but if you do, please try the protocol and report back. Let us know if you’re successful, because we would love to get more data and hone the protocol.” MeV