Imagine being struck by lightning, not once, not twice, not three or four or even five times, but 17 times in three years.
That’s essentially what happened on a Standardbred breeding farm in northeastern Pennsylvania from 2014 through 2016, when 17 out of 28 foals were born with dysphagia, a condition where the foal aspirates milk into its lungs when it tries to nurse. This condition is rare, estimated as occurring in less than 1 percent of foal births.
Kathleen Rory Mullen, DVM, DACVIM, was doing her internal medicine residency at the Cornell University College of Veterinary Medicine (New York), where many of the foals were brought for treatment.
“We started to see a number of these foals from one particular farm, and then in March 2014 became very concerned when five out of the 10 foals born on this farm exhibited signs of dysphagia,” said Mullen, who is now at the Littleton Equine Medical Center (Colorado). “They were also very calm and subdued in their mentation; this is a very unusual syndrome.”
In speaking with the farm manager, the team at Cornell learned that this particular breeding operation also had a farm in New York, but no incidences of dysphagia occurred there.
“In further conversations with the farm manager, we learned the farm in Pennsylvania was located in area of active [fracking],” said Mullen. “We became concerned that maybe the dysphagia and fracking could be related.”
Fracking is banned in New York.
Hydraulic fracturing, more commonly known as fracking—or “unconventional natural gas development”—is a method of extracting natural gas and oil by injecting large quantities of water, chemicals and sand into rock formations at pressures high enough to crack the rocks. There have been many concerns raised about the impact fracking has on the health of humans living in close proximity to UNGD operations, including increased adverse pregnancy outcomes, hospitalizations, asthma exacerbations, cardiovascular disease indicators, increased rates of sexually transmitted diseases and traffic accidents. Studies have also shown an association between congenital defects and how close pregnant women lived to UNGD operations.
The researchers decided to study the foals born at the New York and Pennsylvania farms and compare the dysphagic foals with the normal ones. They first wanted to rule out all other possible causes of dysphagia, which can include oropharyngeal or esophageal malformations (the most common being a cleft palate), prematurity, septicemia, selenium or lead toxicity, and neonatal encephalopathy (“dummy foal” syndrome).
“We examined every foal with an endoscope to be sure there weren’t any malformations,” said Mullen. “We knew their breeding dates, so we knew they weren’t premature. We did blood cultures to make sure they weren’t septic. We measured selenium levels, their lead levels. They did not display other signs of neonatal encephalopathy, so we were able to rule that out.”
The researchers also examined environmental factors on the two farms. Horses at both facilities were fed hay and grain from the same source, but they consumed different water and pasture. Mares also traveled between the farms, occasionally spending part of their pregnancies at one location before moving to the other.
Over 21 months, researchers took blood and tissue samples from mares and foals; analyzed grain, feed and pasture soil; and took continuous passive samples of air and water at the farms. Both farms used well water. The New York farm had a single well; the Pennsylvania farm had two wells, and their water output was combined. The Pennsylvania farm also had 28 gas wells where fracking occurred within a 6.2-mile radius. The closest gas well was located about one-third of a mile from one of the farm’s water wells and a quarter of a mile from the other.
Sixty-nine foals were born at the two farms during the study period, from 2014 to 2016. Of those, 17 were dysphagic (all born in Pennsylvania), and 48 were normal (11 born in Pennsylvania and 37 in New York). Two foals at each farm were diagnosed with dummy foal syndrome and were excluded from the study.
No significant differences were found in the hay, grain or pasture at the two farms. But elevated levels of four polycyclic aromatic hydrocarbons, which are chemicals associated with the fracking process, were found in the well water at the Pennsylvania farm.
The researchers found a strong association between dysphagia and foal gender—13 (or 76%) of the dysphagic foals were colts. They also found that the more time a mare spent on the Pennsylvania farm, especially in mid- to late gestation, the more likely she was to have a dysphagic foal.
Blood and tissue samples didn’t show any remarkable differences between normal and dysphagic foals, nor were there major differences in physical parameters like gestational age, birth weight, height, rectal temperature or pulse rate, but researchers did note that dysphagic foals had a decreased respiration rate at birth—24 breaths per minute compared to 48 breaths per minute in normal foals.
Mullen said that normally when veterinarians see dysphagic foals, the condition only persists for a few hours or a day.
“What was remarkable about these foals is the length of time that they were dysphagic and also the fact that they seemed a lot calmer than normal foals,” she said. “As a veterinarian, it’s nice to work on foals that are really calm, but they did seem abnormal in their subdued mentation. One of our thoughts was that it really suggested a neurological basis for the syndrome. We weren’t seeing any structural problems in the throat that would have prevented them from swallowing properly, so we wondered if it was more of a central nervous system issue, and the subdued mentation would suggest that.
“When we were able to demonstrate that the affected farm had higher levels of PAHs in the water, it was interesting to us because in other experimental studies, exposure to PAHs can adversely affect motor and behavior functions, so this sort of fit with what we were
seeing,” Mullen continued.
All of the dysphagic foals in the study survived and did develop normally. Fourteen of the 17 were eventually able to nurse; the other three never could nurse off their dams but could drink milk from a pan. Mullen also helped conduct a subsequent study that will soon be published and found no significant difference in the racing performance of the affected foals when compared to unaffected foals.
“It doesn’t seem like there were long-term consequences, at least in terms of racing performance, but the foals were sick as neonates, and of course it’s a huge expense for the farm owner to have that many horses treated,” Mullen said.
The researchers also noted that two significant management changes took place during the course of the study. In August 2015 (after the foaling season had ended), a water filtration and treatment system was installed on the Pennsylvania farm. After that point, the levels of PAHs in the Pennsylvania farm’s water dropped and were then comparable to the New York farm. Also, starting in January 2016, mares that were bred in New York and subsequently moved to Pennsylvania only spent the last four to six weeks of their pregnancy in Pennsylvania, compared to previous years when they typically spent four to six months in Pennsylvania.
Those two changes eliminated incidents of dysphagia at the Pennsylvania farm.
Mullen cautioned that farm owners shouldn’t feel like they need to rush to install water filtration systems to protect their livestock.
“This is kind of the first study to investigate this multiyear outbreak of neonatal dysphagia,” she said. “What I would say is that if horse or other livestock owners have concerns about their animals’ health, they really should consult their veterinarian to help identify the causes, and to take into consideration that this was a weird outbreak of an unusual syndrome, and it was worth testing the water, the air, the feed, the soil. So it hopefully brings to light that there are many potential causes, and it’s worth looking into the environment.”
She also noted that horses can be particularly useful as models for human health and environmental toxicity because their reproductive systems are somewhat similar to humans’, and, due to their size, they breathe in large amounts of air and consume large amounts of feed and water daily.
“So they’re potentially exposed to a lot of environmental toxins, and the accumulation of environmental chemicals in horses’ tissues may be more rapid just because they’re so large,” Mullen said.
“The other thing that makes horses a good sentinel is that they tend to live in close proximity to humans,” she added. “We spend a lot of time with our horses; we share a lot of things with them.”
Environmental surveillance and adverse neonatal health outcomes in foals born near unconventional natural gas development activity
Kathleen R. Mullen, Brianna N. Rivera, Lane G. Tidwell,
Renata Ivanek, Kim A. Anderson, Dorothy M. Ainsworth
Science of the Total Environment
This article ran in the Sept. 7 & 14, 2020, Fall Horse Care issue of The Chronicle of the Horse.
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