Latex exposure could be detrimental to a horse’s respiratory health. That’s the surprising discovery from Morris Animal Foundation-funded research at the Royal Agricultural University and University of Nottingham. While further investigation is needed, researchers say latex could be among the allergens responsible for causing severe equine asthma (sEA), a serious horse ailment with limited treatment options. The team published their findings in the Nature journal Scientific Reports.

The finding came from a larger study that applied a new, more comprehensive microarray platform to determine the precise allergens within horses’ stable dust that elicit sEA. Researchers tested nearly 400 extracts and proteins associated with the equine environment on blood samples from 138 horses from Switzerland, France, the United States, and Canada.

The study revealed several previously suspected allergens, such as pollen, mold and insect proteins, are likely involved in sEA, but the most surprising finding was the implication that natural rubber latex allergies might also play a role in equine asthma. In fact, four of the five most significant allergens associated with sEA were latex proteins. The fifth was a protein from Aspergillus fumigatus, a common fungus previously linked with sEA. Until now, latex had not been tested due to limitations associated with classical allergen assessment methods.

“Research to date has generally implicated fungi and bacteria as the predominant allergens associated with sEA, so this was a little unexpected,” said the lead author on the paper, Samuel White, Ph.D., senior lecturer at Nottingham Trent University. “We would need to learn more about how these allergens affect actual predisposed horses, but avoidance of latex allergens may still be beneficial.”

Horses primarily come into contact with natural rubber latex on artificial riding surfaces, like arenas and racetracks. Urbanized environments, which also have higher levels of breathable latex from car tires, have been identified as a risk factor in sEA, as well.

The high level of breathable dust associated with equines training on artificial surfaces has already been linked with chronic bronchitis, inflammation and oxidative stress in riding instructors, and latex allergies have long been associated with a variety of respiratory conditions in humans, including asthma.

Severe equine asthma, which closely resembles human asthma, is a debilitating and chronic allergic respiratory condition. Diagnosed in all breeds, it affects 14% of horses in the northern hemisphere. When exposed to allergens, these horses can experience inflammation and constriction of the airways, as well as excessive mucus production. sEA also is known as heaves, recurrent airway obstruction (RAO) and chronic obstructive pulmonary disease (COPD).

“This new finding highlights the need to better understand the potential health effects of the environments we expose our horses to,” said Janet Patterson-Kane, BVSc, Ph.D., FRCVS, who is the Morris Animal Foundation’s chief scientific officer. “It’s crucial that we identify which allergens might cause them distress so we know what to avoid, as well as develop appropriate treatments.”

The team plans to conduct further research to establish exposure levels of latex in a horse’s daily environment and demonstrate the benefit of avoiding latex.

Morris Animal Foundation is funding other studies to address equine asthma. One is investigating if targeting a specific protein is a viable new therapeutic strategy to treat the condition. Another is examining differences in mast cell subtypes found in the airways of healthy and asthmatic horses to help identify better diagnostic and treatment strategies for equine asthma.

Morris Animal Foundation’s mission is to bridge science and resources to advance the health of animals. Founded by a veterinarian in 1948, it has funded and conducted critical health studies for the benefit of all animals. Learn more at www.morrisanimalfoundation.org.

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Learn more about the differences between terms used for respiratory disease in the horse, such as heaves, chronic obstructive pulmonary disorder (COPD), bronchiolitis, small airway disease, recurrent airway obstruction (RAO), inflammatory airway disease (IAD), and most recently, equine asthma.

For nearly as long as horses have been domesticated, the relationship between barn confinement and respiratory disease, such as equine asthma, in the horse has been recognized. This relationship is intuitive, especially when we consider that deep in the lung, where the blood takes up oxygen, the barrier between the outside air and the horse’s circulation is as thin as a couple of cells.

The surface area of this gas-exchange region of the lung has on average a surface area of 2,500 square meters (26,900 square feet), equal to nearly half a football field. The response of the lung’s immune system to inhaled air results in a number of diseases in both humans and horses. Many of the occupational respiratory diseases in humans are associated with agriculture due to exposure to organic dusts. Dust in agricultural settings, including the horse barn, are rich in substances such as endotoxin and fungi that can drive inflammation.

Depending on when the conversation took place, owners consulting their veterinarians about respiratory disease in their horse will have heard many terms applied to this problem: broken wind, heaves, chronic obstructive pulmonary disorder (COPD), bronchiolitis, small airway disease, recurrent airway obstruction (RAO), inflammatory airway disease (IAD), and most recently, equine asthma. Along the way, distinctions have been drawn between those horses that develop difficulty breathing at rest (heaves, RAO, severe equine asthma) and those that do not (IAD, mild equine asthma). While potentially leading to confusion for the horse owner, the changing terminology actually reflects improvements in veterinary knowledge.

While the term COPD was applied to reflect the obstruction or blocked airflow that can occur in severe cases, this term was discarded due to the differences with the human disease. In humans, COPD is mainly a consequence of cigarette smoke and is characterized by structural changes within the lung that are absent in the horse. While the terms recurrent airway obstruction and inflammatory airway disease are descriptively accurate, they are not necessarily terms that immediately help the horse owner to understand the disease process.

A More Relatable Term for Respiratory Disease

Due to its many similarities with the human disease, the term equine asthma has most recently been adopted. Like human asthma, equine asthma is triggered by inhalation of dust that contains allergens and other irritants, and like human asthma, the cough and difficulty breathing can be reversed in the short term by medications, often delivered by inhalers, or in the long term by removal from the offending dust. Also similar to asthma in humans, the response of the horse’s airway to inhaled dust can vary widely. In some highly susceptible horses, inhalation of even small amounts of dust in the barn environment or airborne allergens (e.g., pollen, molds) at pasture can cause severe inflammation and difficulty breathing due to the accumulation of mucus and narrowing of the airways. There is no known cure for these “severely asthmatic” horses, and they require special management for the duration of their life span.

In other horses, the inflammation is milder, with occasional coughing and decreased performance. Respiratory problems in these “mildly asthmatic” horses often become apparent only when the horse is asked to perform athletically and may resolve over time. Those horses with mild asthma do not necessarily go on to become severely asthmatic.

While susceptibility varies widely, any horse (or person) exposed to enough dust will develop inflammation in the airway. In the case of stabled horses, dust exposure is mostly due to hay. Those horses with severe asthma often require that hay be completely removed from the diet and that the horses be removed from confinement to the barn altogether.

In the milder cases, decreasing the dust released from hay by soaking or steaming may improve airway health. As soaking has a number of draw backs, high temperature steaming is becoming the preferred method to reduce exposure to the dust from hay. At Purdue University College of Veterinary Medicine, we use a Haygain hay steamer, which has been shown to reduce respirable dust by 98%.

Article provided by Haygain, manufacturers of Haygain Hay Steamers and ComfortStall Orthopedic Sealed Flooring. For more information, visit www.haygain.com.

Further Reading

• Breakthrough in Identifying Equine Asthma Allergens
• Waiting to Inhale
• Ask the Vet: Allergy Symptoms in Horses

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