By T. D. Thornton
A spike in foal deaths caused by nocardioform placentitis has been reported in Kentucky as the first month of the 2020 Thoroughbred foaling season comes to a close.
As of late Thursday afternoon, the number of equine abortions reported by the University of Kentucky Veterinary Diagnostic Laboratory (UKVDL) stood at 44. The UKVDL's statewide map of the foal deaths listed 29 in Fayette County alone. Other abortions listed by county include six each in Woodford and Bourbon, and one each in Shelby, Scott, and Harrison. You can view the interactive UKVDL map here. Note that it accounts for all reported equine deaths, and is not Thoroughbred-specific.
Dr. Barry Ball, a veterinarian with the University of Kentucky's Gluck Equine Research Center who holds the Albert G. Clay Endowed Chair in Equine Reproduction, told TDN that in a normal year, the number of foal deaths from nocardioform placentitis might be in the single digits or low teens by this time of the season.
“This would be a significant upturn from those numbers, and right now it's looking like it's on par with numbers reported in 2017 and 2011,” said Ball, referring to Kentucky's two most recent breeding seasons that saw spikes in foal deaths from nocardioform placentitis. “Both of those years were significant upturns, and this certainly looks like it's heading in that direction.”
Dr. Karen Wolfsdorf, a reproduction specialist at Hagyard Equine Medical Institute, told TDN the situation calls for vigilance–not panic–at this point.
“While I do think we have an increase in incidence this year, it's still not the worst that it's been, or at 'epidemic' levels,” Wolfsdorf said. “It's just something to be aware of that is on the increase this year.”
Wolfsdorf gave an overview of what nocardioform placentitis is, how it's diagnosed, and what warning symptoms Thoroughbred farm personnel can look for in pregnant mares.
“Nocardioform placentitis is a group of organisms that forms mucous production that then causes separation of the placenta from the mare's uterus,” Wolfsdorf explained. “So it stops nutrients and oxygen getting from the mare to the fetus, which can damage and be life-threatening to the foal.”
Foals can either be stillborn or born in a weakened state that requires euthanization. Some foals are “born alive and do perfectly fine” in cases where mares have only a small lesion, Wolfsdorf said.
“There are two main types of nocardioform placentitis that we see most commonly,” Wolfsdorf said. “One is the bacterial organism Crossiela equi. The other one is Amycolatopsis. We tend to see foals either aborted or born a month early with the Crossiela equi, as opposed to Amycolatopsis, where [foals] seem to have a better survival rate or live foal rate. It depends on when the mare is infected or when the lesions start to form as well as how large those lesions are, because that will determine how much nutrients and oxygen that foal is deprived of.”
Wolfsdorf noted that nocardioform placentitis differs from placentitis caused by an “ascending infection,” which is when pathogens get past a mare's vulva to ascend through the reproductive tract.
In nocardioform placentitis, “we don't know how it gets there,” Wolfsdorf said.
“We believe it's in the soil in the environment,” Wolfsdorf continued. “We don't know how it gets to the uterus. But the lesions that you see are pretty characteristic, and they're usually found at the base of the horns of the uterus or in the body of the uterus. This is unlike ascending placentitis.”
The first clinical signs of nocardioform placentitis are usually vaginal discharge and premature lactation.
“Usually how we identify it is when a mare starts to develop a mammary gland prematurely,” Wolfsdorf said. “Usually that's associated with placentitis or twins.”
Wolfsdorf said that if those signs are present, the first step is to rule out ascending placentitis by ultrasound. Then a different ultrasound view will be used to look for the distinctive nocardioform placentitis lesions.
But that diagnostic method is far from perfect.
“It's more of a rule-in than a rule-out process,” Wolfsdorf said. “If [a nocardioform lesion] is there, you can see it. But if it's not there, it doesn't mean that she doesn't have it, because the area where the lesion can be is so small and the surface area of the uterus is so large.”
Ball agreed: “The difficulty with those kinds of clinical signs is that the disease is pretty far progressed by the time you see some of those changes,” he said.
“We don't have good diagnostic techniques for early diagnosis,” Ball added. “That's something that we've been working on for awhile. Ultrasound of the placenta is being used with some success, but the sensitivity of that is uncertain. It may only be useful in relatively late cases, but we are seeing it being used at farms that are at risk ”
Wolfsdorf explained how farm personnel can be on the lookout for those first clinical signs.
“Monitor the mare for premature mammary gland development,” Wolfsdorf said. “And then just practice good husbandry. Look under the tail every day to make sure there are no signs of a discharge there. Make sure the mare is acting and behaving normally.”
Wolfsdorf pointed out that vigilance should also extend to foals that appear totally healthy, underscoring her earlier point about how a foal can be born without complications even if the mare had nocardioform lesions.
“The only way you know sometimes if they had that disease is by examining the placenta,” Wolfsdorf said. “That's another thing farm personnel can do–make sure to turn the placentas inside out both ways, so you look at not only the white shiny side, but you look at the red side, where you're going to see these lesions. And if you see that you're having an increased number of lesions, then maybe it's time to be proactive and ultrasound your mares transabdominally to see if you can identify any more lesions.”
“It's a disease that although there's been a lot of research to try and determine where it comes from, it still eludes us,” Wolfsdorf said. “It's very farm-dependent, area-dependent. We don't know why some farms have it and some farms don't have it.”
Both Ball and Wolfsdorf noted there appears to be a spike of the disease in years when unseasonably warm weather precedes foaling seasons.
“Hot, dry Augusts and Septembers are statistically associated with an increased incidence of the disease in the following winter and spring,” Ball said, noting that he is in the process of completing a 30-year historical study on potential effects of weather on nocardioform placentitis.
“We don't know what the meaning of that association is,” Ball said. “But it's a statistically significant relationship. It doesn't mean it's a cause. It just means that there is some association, and we don't yet understand” what that is.
This past autumn, parts of Kentucky broke dryness and heat records, with a string of rainless, 90-degree days extending through September. On Oct. 1, a National Weather Service meteorologist based in Louisville described conditions statewide as “really, literally, the summer that won't end.”
Ball said future projects he is involved with might yield better clarity.
“Nocardioform placentitis is on our radar. It has been for a long time,” Ball said. “We're finishing a study right now looking at the genome-wide transcript of those kinds of tissues, basically looking at gene expression across the placentas of mares with those diseases compared to controls. We know a lot more about the inflammatory picture associated with it. But that hasn't given us much in the way of clues about the etiology in terms of how this starts.
“We've also done some pretty extensive studies with inoculating mares trying to reproduce the disease,” Ball summed up. “But to date we have not had any success. So we clearly have a lot to learn.”