Feeding the Asthmatic Horse

Dietary adjustments might help horses with recurrent airway obstruction breathe better.

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Feeding the Horse Wit Asthma
Horses with RAO typically do better when kept in pasture. | Photo: Anne M. Eberhardt/The Horse
Q: Last fall and winter my horse had a sporadic cough and sometimes it felt like he couldn’t get enough air when we were working. My vet said that he most likely has allergies and mild recurrent airway obstruction. My horse responded well to veterinary treatment with corticosteroids, but is there something I could do nutritionally to prevent this from happening again this year?

A: Respiratory health is crucial to your horse’s well-being and performance ability. In fact, the respiratory system is a major limiter of performance due to the fact that relatively limited improvements in respiratory function can be made through training. Therefore, it is of utmost importance to care for a horse’s respiratory system.

First of all, you need to work with your horse’s veterinarian to monitor the condition and ensure that it’s not getting worse. Recurrent airway obstruction (RAO, a form of equine asthma syndrome and previously referred to as heaves) is never really cured but in many cases can be managed effectively to reduce clinical signs. If left untreated damage to the lung tissue becomes irreversible.

Fact Sheet: Equine Asthma Syndrome (Free Download)
Fact Sheet: Equine Asthma Syndrome (Free Download)

Since RAO is most commonly triggered by molds, dust, and pollen, effective management starts with limiting your horse’s exposure to these allergens. Given the time of year that you are noticing issues I suspect that dust and mold are bigger problems for your horse than pollen. However some plants do release pollen in the fall and you should work with your vet to narrow down exactly what your horse’s specific triggers are.

Hay is thought to be a major area of concern for horses with RAO, because even the cleanest looking hay will contain some level of dust and mold spores. Ensuring hay is as clean as possible is a vital first step.

Research has shown that soaking or steaming hay before feeding can significantly reduce respirable mold spores. High-temperature steaming is the most effective and does not greatly alter the hay’s nutritional composition.

When soaking hay, it’s not enough to just wet it—you must completely submerge the hay into water. However, extensive soaking is not necessary. Research has shown that completely submerging hay in a bucket of water (rather than hosing it down) more than halves the respirable dust concentration as compared to feeding dry hay and that there‘s no significant difference if the hay is soaked for 16 hours versus immersed in a bucket of water and then fed.

High-temperature steaming (over 200F) has been shown to reduce microbial contamination and respirable particles to almost zero. While some people create homemade steamers these are unlikely to get hot enough and there could be an increased fire risk. For this reason I recommend investing in a commercially manufactured steamer made specifically for the purpose.

As a separate consideration some horses seem to prefer steamed hay over soaked hay, so if your horse is a picky eater this might be something to keep in mind.

And, regardless of whether you soak or steam, be sure to remove any unconsumed hay from your horse’s stall or pasture before it gets the chance to generate mold.

If neither soaking nor steaming hay are a viable option you might need to feed pelleted hay, because pellets are generally less dusty especially if fed wet. One downside to pellets is that they do not take as much chewing as hay and horses tend to digest them more easily, so you might find that your horse starts to gain weight requiring a reduction in the amount being fed. Of course these are positives if you are feeding a hard keeper or a horse with poor dentition. To make eating pellets take longer you can almost simulate grazing by using a commercially available automatic pellet dispensers, which dispense a predetermined amount of pellets at scheduled intervals throughout the day.

Another consideration with a RAO horse is type of bedding used when he’s stalled. Avoid straw due to potentially high mold spore levels. Low-dust bedding options such as some shavings, paper and bare rubber mats are preferable options.

Part of the challenge in managing horses with RAO is that in a barn environment. Even if you are properly managing your horse’s forage and bedding, the barn air is affected by what other horses are being fed and bedded on.

Horses with RAO typically do better when kept in pasture, away from dusty barns with limited air flow. If your horse is kept out in the spring and summer and then spends more time indoors in the fall and winter when his clinical are worse it might be worth investigating ways to keep him out as much as possible, even in the winter. Be cautious of feeding pastured horses with RAO using round bales of hay. Horses often burrow their heads into such bales exposing themselves to dust and spores when eating and these bales are impossible to soak or steam.

If pasture access in the winter is not an option look at ways you can improve air quality in the barn. House him in the end stall nearest the big barn doors for maximum ventilation. Try to ensure that he is removed from the barn when stalls are being mucked and aisleways cleaned. Do not use blowers to clean aisles, sweep instead. Ensure that stalls are frequently mucked out and all wet areas removed as ammonia is a major irritant for respiratory tissue. Barns where large amounts of high protein legumes, such as alfalfa, are fed can have particularly high levels of ammonia due to increased urine production. Therefore, try to avoid feeding excessive dietary protein. These are good management practices regardless of whether your horse has RAO because minimizing contact with airborne dust, molds and other allergens reduces the chance that a horse will develop RAO in the future.

Feeding omega-3 fatty acids especially those rich in DHA (docosahexaenoic acid) have been shown in research to improve clinical signs of RAO. In a study of horses with RAO that were switched to a pelleted diet and fed a supplement containing 1.5 to 3 grams of DHA or a placebo each day for two months reduced coughing, decreased respiratory effort (by 48% vs 27% for placebo), and a significant decrease in neutrophils in bronchoalveolar lavage was found (from 23 to 9% vs placebo which increased from 11 to 17%). It should be noted that the supplement used also contained vitamin C which is known to impact immune function, as well as MSM and a mushroom complex. It is, therefore, difficult to assess whether the response was due solely to the DHA. However, other studies have shown that feeding sources of omega-3 fatty acids can help maintain a normal inflammatory response and therefore feeding supplemental DHA may be of benefit to horses with respiratory conditions such as RAO. For best results it’s probably best to start supplementation before clinical signs are expected rather than trying to reduce inflammation that is already established.


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Written by:

Clair Thunes, PhD, is an equine nutritionist who owns Clarity Equine Nutrition, based in Gilbert, Arizona. She works as a consultant with owners/trainers and veterinarians across the United States and globally to take the guesswork out of feeding horses and provides services to select companies. As a nutritionist she works with all equids, from WEG competitors to Miniature donkeys and everything in between. Born in England, she earned her undergraduate degree at Edinburgh University, in Scotland, and her master’s and doctorate in nutrition at the University of California, Davis. Growing up, she competed in a wide array of disciplines and was an active member of the U.K. Pony Club. Today, she serves as the district commissioner for the Salt River Pony Club.

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