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“We investigated a clustering of neonatal dysphagia at a well-managed Standardbred broodmare farm located in northeastern Pennsylvania,” said Kathleen R. Mullen, DVM, MS, Dipl. ACVIM. “In addition … the foals exhibited a subdued mentation but had good suckle reflexes.”
Mullen, a practitioner at Littleton Equine Medical Center, in Colorado, completed the research when she was an equine internal medicine resident at Cornell University, in Ithaca, New York. She presented her findings as part of the 2020 American Association of Equine Practitioners Convention, which is being held virtually.
Over a three-year period (2012-2014), Mullen said the farm saw two of eight, two of six, and five of 10 foals born from nine mares—and bred to seven stallions—had been dysphagic. “These problems combined with the farm’s proximity to unconventional natural gas development sites led us to seek environmental chemical exposures as the cause of dysphagia.”
Unconventional Natural Gas Development and Gestation (In a Nutshell)
Fracking, Mullen explained, involves drilling vertically and then horizontally to access natural gas reserves. Fluids are injected under high pressure to fracture the shale bed and release the trapped gas, which flows back to the surface with the injected fluids.
“Typically, the chemicals used in the fracking process are not disclosed by the companies,” she said. “In a 2017 study, 20 polycyclic aromatic hydrocarbons (chemicals formed during the incomplete burning of coal, oil and gas, garbage, or other organic substances) were identified in the fracking flowback and produced water. Many of these chemicals … are classified as endocrine disrupters displaying estrogenic or androgenic activities (hormonal effects), others … are neurodevelopmental toxicants.”
She also noted that researchers studying infants have found an association between UNGD and congenital birth defects, severity of preterm birth, decreased birth weights, and decreased Apgar scores—obtained using a method to quickly assess the health of newborn children against infant mortality. “Chemicals and metals associated with the process lead to developmental learning and behavioral disabilities in children,” she said.
Additionally, physicians have associated prenatal polycyclic aromatic hydrocarbon exposure in pregnant women with fetal growth reduction, cognitive developmental delay, reduced IQ, and behavioral disorders in children.
The 85-acre breeding farm’s closest natural gas well, which went into production in the spring of 2011, is 5,100 feet deep, and the farm’s two water wells are 126 and 200 feet deep. The water wells are 1,422 and 1,714 feet (.27 and .32 miles) from the gas well pad, and six gas well pads sit within a 2.5-mile radius of the farm.
The Study
Mullen had the perfect control group available for a prospective study: The farm has a similar-sized sister property 250 miles east in New York that follows the same breeding practices and uses the same sources for feed, hay, and bedding. Some of the mares bred at the New York farm spend the mid- to late parts of their pregnancies at the Pennsylvania farm. There are no gas well pads near the New York farm (fracking is banned in that state, and the farm is not near the Pennsylvania border), and the property hasn’t seen any of the foal problems.
The researchers looked at the time the mares spent on each farm prior to foaling. They also tested for water- and airborne chemicals every six weeks over an 18-month period on both farms by deploying passive sampling devices in well water and in stationary monitors, respectively.
Of the 17 dysphagic foals, all were born at the Pennsylvania farm and 14 recovered with treatment, gaining their ability to suckle effectively, with a median 11-day dysphagia duration (range from four to 37 days). Three foals remained unable to suckle after 16 days and, so, were weaned from their dams and drank milk from a pan. The veterinarians used post-feeding tracheoscopy to confirm the foals’ dysphagia had resolved.
Mullen and her colleagues found no statistically significant differences in physical exam parameters between the dysphagic and control foals except foals with dysphagia had lower median respiratory rates at birth and lower (but still within normal range) modified Apgar scores.
Using one statistical model, they found “the odds of dysphagia were associated with mares residing on the Pennsylvania farm for a longer percentage of gestation,” said Mullen. “This syndrome also appeared to be gender-associated, with colts having increased risk of dysphasia compared to fillies.”
The researchers found no clinically significant differences when they compared feed and soil samples or the polycyclic aromatic hydrocarbons measured in the air. They did find differences, however, between the Pennsylvania and New York farms’ water supplies; sampling of well water revealed higher concentrations of polycyclic aromatic hydrocarbons on the Pennsylvania farm than on the New York farm. Installing a water filtration and treatment system lowered several of those compounds and eliminated the developmental defect.
Finally, the research team compared race performance of the normal and previously dysphagic foals. Twenty-six of the 42 race-eligible foals born on the Pennsylvania farm (62%) raced, which wasn’t statistically significantly different from the 70% of race-eligible foals from the New York farm that raced. A foal that had been dysphagic did not have lower odds of racing than an unaffected foal, regardless of whether the researchers considered all unaffected foals or just those from the Pennsylvania farm. Formerly dysphagic foals began racing at a median age of 2, which didn’t differ from the other foals or those healthy foals just at the Pennsylvania farm. They saw statistically significant similarities across the horses’ race performance, as well.
“Treatment of neonatal dysphagia associated with maternal polycyclic aromatic hydrocarbon exposure is a financial burden for the horse owner,” she said, referring to the time many of the foals spent in the veterinary hospital receiving supportive treatment. “The athleticism of formerly dysphasia foals does not appear to be negatively impacted as measured by the age of first race, earnings per start index, or the speed index.”
Mullen said she was grateful for the study’s funding source—the National Institute of Environmental Health Sciences—and the opportunity to share this research with other practitioners to find out if there have been other farm outbreaks of dysphagia or other equine health issues associated with national resource mining or environmental toxin exposures. “Understanding the linkages among human, animal, and environmental health is vital to providing optimal outcomes for all,” she said. Veterinarians can reach her via email at kmullen@littletonequine.com.
