From my counter, I watch Florida horse owners grapple with a number of issues that are particularly difficult to manage in our climate – from gnats to fungal infections, and of course the non-sweaters. Among these, there is one disease in particular that gets Florida horses (and their owners) down – heaves. I hear so much about it, that this week I stole Dr. King’s Naughty Pony article that explains heaves, inside and out!
Heaves, formally known as Recurrent Airway Obstruction (RAO), is an allergic respiratory disease similar to asthma in humans. Like with asthma, the primary symptom is that of respiratory distress. The high load of plant and mold allergens, exacerbated by the intense heat, makes life especially tough for a ‘heavey’ horse living in Florida. Heaves was first recognized as being associated with horses that were stabled in dusty barns and fed hay. The organic dusts associated with bedding and hay – containing molds, allergens, endotoxins, and small particulates, initiate the inflammatory cycle in the airways. In Florida, plant allergens alone can get your horse heavey – symptoms are usually worse in the fall for this reason (although the summer heat doesn’t help either).
The first response is for the airways to constrict – termed bronchospasm, which is the primary response with human asthma. The airways also produce mucus to try to trap the allergens, and move them back out of the airway. However, in the narrowed airways of the lungs, these mucus plugs lodge, closing off the path to the downstream air sacs (alveoli). As the horse attempts to move air into the alveoli, where oxygen can pass into the blood, the mucus plugs dislodge and re-lodge. This action is the root of the name Recurrent Airway Obstruction, changed from the old name COPD (chronic obstructive pulmonary disease). Over time, the muscle layer and fibrous scar tissue around the airways thicken, making the lungs less elastic, and less likely to recover. This means that the longer heaves goes unmanaged, the harder it will be to manage down the road. A recent study found that horses with RAO have a more intense response to the histamine control during Intradermal Skin Allergy Testing (ISAT), indicating that histamine is an important component of the allergic response with heaves.
Horses with heaves develop a characteristic appearance. The respiratory rate is increased (normally 12-24 breaths per minute), and the nostrils are wide open and flaring with each breath. The horse’s expression often appears anxious or distressed. With chronicity, the horse uses the abdominal muscles to try to move air, and a double breathing effort is seen in the flank. Over time, the horse develops a “heave line” just under the edge of the ribs from this motion (black arrow). Wheezing, first only heard with a stethoscope, becomes audible just by standing near the horse. The horse is losing weight by this point, and may extend the head and neck in its attempt to move air. Early signs may only be seen with exercise, particularly in dusty arenas. These include coughing, reduced exercise tolerance, and a delayed recovery from exercise (eg, respiratory rate does not return to normal in 5-10 minutes).
Diagnosis is generally straightforward, characteristic wheezing on expiration is heard with a stethoscope. A rebreathing exam (performed with a trash bag over the horse’s nose) and/or exercise may be required to bring these sounds out to an audible level. Definitive diagnosis is performed with a BAL (bronchoalveolar lavage), where a small amount of fluid is put into then recovered from the deep airways. The cells from the fluid are examined for the presence of inflammatory cells. Intradermal Allergy Testing, now offered by Springhill Equine, is an important diagnostic step to management and therapy of heaves.
Management of heaves is multi-factorial and challenging (that means there is no miracle shot). Housing is an important consideration – on pasture is usually preferable to stabled, however, it is important to know the source of the horse’s allergic response. For example, a horse who is allergic to dusts and molds should be managed differently from a horse allergic to trees and weeds – and this is where Intradermal Allergy Testing comes in (see story above). Another benefit of allergy testing is immunotherapy – an individualized prescription program developed based on the findings of your horse’s intradermal test. These tiny shots teach your horse’s immune system to hold its’ horses when responding to these everyday particles. Once we know what your horse is most allergic to, targeted avoidance also becomes easier. For example, you can walk your pasture knowing that it’s crucial to get up all the pigweed. Or, you can improve ventilation and soak your hay for 5-15 minutes prior to feeding to minimize molds and dusts. Other management techniques to reduce dusts include reduced sweeping (which stirs up dust), watering arenas, and removing roundbales. Rolled or processed grains should be replaced with soaked pellets. Alfalfa pellets and cubes, as well as whole grains, have lower amounts of dusts. However, consider your horse’s response to alfalfa during the allergy test – food allergies exist in horses too!
Finally, the mainstay of heaves management is steroid therapy. Whether using dexamethasone, prednisolone, or triamcinolone, our last desperate attempt to quiet the allergic response is to suppress the immune system with steroids. Side effects, which include worsening or inciting laminitis or infections, make steroid use less-than-ideal in many patients. However, they work much better than non-steroidal anti-inflammatories, like ‘bute’ (phenylbutazone) and ‘Banamine’ (Flunixin meglumine). We reach out to aerosolized steroids like Beclomethasone and Fluticasone in some cases – administered via a specialized horse mask. Attempts to manage heaves with other medications, such as antihistamines like hydroxyzine, have had variable success. Bronchodilators, like clenbuterol or albuterol, are generally only used as rescue medications for acute attacks, or prior to administering aerosol medications. However, the new evidence regarding the histamine response in ISAT indicates that antihistamine therapy may be worth reconsidering when managing the challenging heaves horse.
In summary, heaves (RAO) is a challenging and debilitating disorder to which horses in Florida are especially at risk. We hold renewed hope in managing it with the introduction of Intradermal Allergy Testing at Springhill Equine, allowing us to not only identify allergens to avoid, but also to provide an immunotherapy prescription for your horse.
Please contact Springhill Equine if you have any questions regarding management of heaves, or regarding allergy testing your horse! As always, may your litter box be clean and your food bowl full!