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Heaves And Heart Failure: Is There A Connection?

A new study out of Canada shows that uncontrolled respiratory disease in horses may put them at risk for pulmonary artery changes that lead to heart failure.

People with severe asthma can have thickening of the pulmonary arteries, which leads to pulmonary hypertension. Severe equine asthma, like asthma in humans, presents as airway inflammation, coughing and labored breathing; therefore it's feasible that equine asthma can also lead to pulmonary artery thickening, reports EQUUS magazine.

Often called “heaves,” this condition is triggered by mold or dust in hay or the environment. The affected horse must be managed so exposure to these environmental triggers is minimized. Best management practices for horses with heaves include as much turnout as possible, removing horses from stalls when they are cleaned and rebedded, and soaking hay.

Dr. Serena Ceriotti and other researchers at the University of Montreal looked at multiple post-mortem lung samples from 18 horses — six that were in heaves episodes when they died; six with heaves that was in remission because of management practices; and six with no history of heaves.

The scientists measured arterial thickness and found that the horses experiencing active heaves episodes had thicker arteries than the other horses.

Though it's unclear why the arteries thicken, experiments in rodents suggest the low oxygen content and inflammation may increase smooth muscle in the arterial wall. This increase in the muscle decreases the area for blood to flow and may increase muscle contractions, which leads to pulmonary hypertension, minimizing blood flow and limiting cardiac function. This condition can eventually lead to the enlargement and failure of the right ventricle of the heart.

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A second portion of the study tested two potential pulmonary hypertension treatments on live horses. One involved reducing the horse's exposure to dust for an entire year and on using hay alternatives. The second used the medication fluticasone for six months then added in dust-control strategies for an additional six months.

The researchers found that both treatments lead to a reversal in artery wall thickness, but this could only be seen once the dust control measurements were enacted. The team notes that hay is the main trigger for heaves; often just changing the horse's diet to include a forage alternative is enough to control the disease.

They conclude that arterial wall remodeling is reversible, but only with strict dust control measures. Inhaled corticosteroids can rapidly improve a horse in experiencing a heaves flareup, but an improved environment is the only way to manage the condition long term.

Peat Moss Or Wood Shavings: Bedding For Asthmatic Horses

The natural dust and molds found in bedding material often intensify the clinical signs of horses with asthma. Bedding materials differ in the inhalable and respirable particles they release, just as they have variable absorptive qualities and aesthetic appeal. While horsemen the world over use straw and wood shavings extensively, the popularity of peat moss often coincides with where it is easily obtained, such as in Nordic and Baltic countries. Finnish researchers recently investigated if the use of wood shavings and peat moss as bedding had different effects on the respiratory health of horses.

Researchers chose 32 clinically healthy riding-school horses for this study. The daily schedule of the horses included 18 hours in a stall, 2 to 3 hours of exercise in an indoor arena, and 3 to 4 hours outside in sandy paddocks. Horses were stabled in identically sized stalls with a common airspace and with the same level of ventilation. Researchers maintained bedding at a depth of approximately 4 inches, with new bedding added each day after stall cleaning to keep the depth consistent. Horses stayed on each bedding material for 35 days. Diets consisted of haylage and pelleted concentrate. Horses ate the haylage off the stall floor. Researchers performed lower airway endoscopy and sampling (tracheal wash and bronchoalveolar lavage fluid) for cytological examination at the end of each bedding period.

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While researchers found no differences in respiratory rate or tracheal mucus accumulation between treatments, horses bedded on wood shavings had more neutrophils in their tracheal washes and bronchoalveolar lavage fluid. The researchers concluded that “between the two bedding materials used in this study, peat caused less neutrophilic lower airway inflammation in horses.”

Asthmatic horses should be kept outside as much as possible, a management strategy that keeps many horses from having severe symptoms of asthma. High-performance horses must often be stabled to accommodate training and competition schedules. In these instances, medical management of asthma should be guided by a veterinarian well versed in the respiratory care of horses. Management decisions are often based on reducing inhalable dust and molds, which includes careful selection of bedding and forages.

Aside from forage type (haylage versus dry hay) or treatment (soaking versus high-temperature steaming), another nutritional consideration is the use of long-chain omega-3 fatty acids, particularly docosahexaenoic acid (DHA). In a consensus statement from the American College of Veterinary Internal Medicine, experts recommend the use of omega-3 fatty acids as a way to control airway inflammation.^° The most potent sources of omega-3 fatty acids available for horses are marine-derived oils, such as EO-3.

^*Monki, J., M. Sasstamoinen, N. Karikoski, M. Rajamaki, M. Roaekallio, J. Junnila, S. Sarkjarvi, M. Norring, A. Valros, S. Oranen Ben Fatma, and A. Mykkanen. 2021. Effects of bedding material on equine lower airway inflammation: A crossover study comparing peat and wood shavings. Frontiers in Veterinary Science 8:656814.

Fall Allergies Can Trigger Equine Asthma, Impact Performance

Just as many humans start to sneeze in the fall, horses also can be affected by seasonal allergies.

Sometimes this is apparent by coughing, but other times, according to Laurent Couëtil, professor of large animal internal medicine in Purdue University's College of Veterinary Medicine, the only sign is that their performance suffers.

Couëtil has spent much of his career treating and researching equine respiratory disease, and he collaborated with three other researchers to argue for the adoption of equine asthma as an official diagnosis in the Equine Veterinary Journal. Equine asthma can flare up as a result of allergies, especially during the fall, which is when many of the traditional spring races were moved.

“We tend to see an increase in horses showing signs of equine asthma during crop harvest season,” he said. “Horses pastured near fields where crops are harvested may be exposed to the dust generated by the combine harvesting crops.” Horses affected by these allergies may develop signs like coughing or increased breathing efforts within a few days of exposure to the dust or allergens and may show impaired performance.

“Other horses with asthma tend to show signs when pollen and molds peak again in the fall,” Couëtil said. “So, the triggers may be different, but horses will show similar symptoms.”

One reason for so many allergy and asthma flare-ups in the fall has to do with feeding. As grass becomes sparse toward the end of the summer or early fall and horses are supplemented with dry hay, more susceptible horses may develop asthma flare-ups.

“Most asthmatic horses are allergic to hay dust,” Couëtil said, “and, therefore, they usually develop clinical signs when fed hay in the barn during the winter months.”

Additionally, feeding round bales is associated with more severe signs because horses are exposed to higher dust levels compared with eating from square bales.

“This is especially true when round bales are left in the field uncovered as they tend to become moldy from exposure to rain and moisture,” Couëtil said.

Couëtil has found that often, less severe asthma symptoms improve when horses are on grass pasture, but during the fall months, this isn't always possible. Feeding low-dust forages can help horses recover and also prevent flare-ups.

“Our recent research demonstrated that athletic horses, such as racehorses, benefit from being fed steamed hay or haylage instead of dry hay,” he said. “These forages result in lower exposure to dust as compared to dry hay, and this translates in lower levels of airway inflammation. Haylage appears to have the strongest beneficial effect, and this effect seems to be linked to higher omega-3 fatty acid content.”

Additional supplementation with nutrients rich in omega-3 fatty acids, like EPA and DHA found in fish oil and algae, can help keep asthmatic horses healthy.

Avoiding exposure to allergy triggers, such as by feeding low-dust forages, can help horses stay healthy and perform at peak levels. During crop harvest season, this might mean keeping the horse in the barn while crops around the stable are harvested.

“If horses continue to show signs of asthma despite environmental management, your veterinarian may prescribe treatment with aerosolized corticosteroids,” Couëtil said.

Taking preventive measures can help minimize horses' exposure to allergens and prevent asthma flare-ups, keeping horses healthy and performing at their best levels.

Couëtil's research is supported by the Grayson Jockey-Club Research Foundation, the state of Indiana and the Purdue Veterinary Medicine research account.