Placentitis is the sneaky foe of many a breeder or broodmare manager. The condition can arrive with no calling card, or such mild symptoms that they're easily missed. By the time a pregnant mare's caretakers are aware of it, it's often too late to save the foal.
It's been the leading cause of pregnancy loss, especially late pregnancy loss, in horses for years.
Dr. Margo Macpherson, professor emeritus at the University of Florida's College of Veterinary Medicine, has been one of many researchers trying to figure out how to stop it in its tracks.
“I call myself a clinician scientist because I'm a clinician first but I want evidence for the things I'm doing in a clinical setting,” Macpherson said.
Placentitis is the inflammation of a mare's placenta, usually as the result of an infectious agent like a bacteria or a virus. The infection causes inflammation which disrupts the structures that protect a gestating foal. There are various subtypes of placentitis and different sources of the infection, but the risk with all of them is that the suddenly-hostile environment will compromise the foal's growth and eventually stimulate a premature delivery or the death of the foal.
Macpherson said there may be some mild vulvar discharge during the mare's pregnancy that could signal a problem, but sometimes there isn't, or it's so minor that managers may not see it. What they do often report is an early development of the mare's mammary glands, well ahead of the projected foaling date. Sometimes breeders learn the mare had placentitis when the foal is aborted.
Even if they're able to catch onto a case before an abortion happens, Macpherson said veterinarians are often unsuccessful in attempts to reverse the damage from the inflammation.
For many years, the standard treatment was a combination of drugs – an antibiotic to try addressing the infection; altrenogest (known commonly as Regu-Mate) to try to avoid premature foaling, and an anti-inflammatory called pentoxifylline which was believed to reduce inflammation and improve blood flow. The trouble was, Macpherson said there wasn't a lot of evidence about how good pentoxifylline was at accomplishing those goals in placentitis cases, and most clinicians didn't want to keep horses on it long-term.
Paula Quinn, long-time breeder of Thoroughbreds and Warmbloods in Florida, has seen her fair share of placentitis cases and has always been curious about what veterinarians prescribed to her horses and why.
“What I like about a teaching hospital [like University of Florida] is they do a lot of research and they're used to explaining things to people and I have a very curious mind and always want to understand things,” said Quinn. “We had a mare over there that unfortunately developed placentitis and the foal did not live in this particular case, but I was asking about the different medications and protocol.”
This was shortly after the Food and Drug Administration approved firocoxib for use in horses with arthritis in 2016. Quinn knew from her research that firocoxib is a nonsteroidal anti-inflammatory that is targeted in the way it works in a horse's body, moreso than familiar NSAIDs like phenylbutazone or flunixin megalamine. Because firocoxib and other medicines like it target only certain types of inflammatory mediators, they don't cause the same gastrointestinal irritation that less targeted nonsteroidals can. That makes them safer choices for longer-term use.
Quinn had a horse with navicular syndrome who had been on firocoxib for some time with no ill effects. She asked Macpherson – have you considered this new anti-inflammatory for use in placentitis?
It was a new idea to Macpherson, because before then, people really only thought about the drug in terms of arthritis, which is also how it's commonly prescribed in humans. Macpherson designed a study to test out how firocoxib may work in this clinical setting, and got funding from the Grayson-Jockey Club Research Foundation to make it a reality. First, she induced placentitis in two groups of mares and gave firocoxib to one of the groups. Then, she measured the levels of various inflammatory mediators in allantoic and amniotic fluid, and found that treated mares had lower concentrations of inflammatory mediators than those who went untreated.
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If you appreciate our work, you can support us by subscribing to our Patreon stream. Learn more.In her next study, she combined firocoxib with an antibiotic and a double dose of Regu-Mate and gave the combination to a group of pregnant mares with placentitis, as a way to test the typical protocol in the field. The group was small, but she said all of them delivered live foals.
Thanks to her research, many clinicians are already using firocoxib as a part of their placentitis treatment program. The next time Quinn had a mare with placentitis, she was surprised to learn that the medication protocol had changed, and reached out to ask Macpherson – was that because of us?
Quinn and her veterinarian gave their mare the trio of medications that included firocoxib, and the mare produced a healthy foal. At a recent Belgian Warmblood inspection, the horse was rated as a Premium Filly.
“Margo and I were laughing that something I had a part in saved one of my own fillies,” said Quinn. “But she's so generous to give me any credit at all, because the work she's put into this has been amazing.”
Quinn said as a horse owner, it's good to know there's a better treatment out there, but she knows the road to solving the problem of placentitis is a long one.
For Macpherson, the next research focus will involve looking for early warning signs that something is wrong before a mare shows outward symptoms.
“I think a big piece of what we're missing is understanding the pathophysiology of the disease and how we can better diagnose it,” said Macpherson, who noted the University of Kentucky has done great work in this are already. “Probably for me, I have a series of years' worth of samples I've collected under different types of conditions. I'd like to look at those samples to see if we can find any biomarkers that are indicative of impending placentitis so that we can do a better job of initiating those treatments and making those treatments more effective. That's a big piece of it, we find placentitis too late. We find it well into the disease process and then it's hard to catch up.”
In the meantime, it's good to know there's an effective, safe protocol out there that can help in some cases – and it's been embraced broadly in the field.
“People are pretty quick to grab onto those treatments,” Macpherson said. “They want something that works better. Grayson-Jockey Club Research Foundation has been very, very good about supporting research problems that have a clinical impact on horses. They're not just a Thoroughbred-based organization, they're looking after the health and welfare of all horses. We happen to see it a lot in Thoroughbreds because we have an older population of mares who have been breeding a long time, but it's everywhere.”
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