A coughing horse always gets your attention. Loud, dramatic, entire-body affairs, equine coughs are impossible to ignore—particularly if you are mounted on the horse at the time.
But the sound and intensity of a cough don't necessarily tell you how significant it is. Most are simply natural attempts to clear a transitory irritant from the respiratory tract; others signal more serious or chronic conditions that can jeopardize long-term health. "If you listen carefully and look for clues-such as the frequency of the cough or how the horse looks otherwise—you can usually determine what type of cough you are dealing with," says Ed Robinson, BVetMed, PhD, director of the Pulmonary Laboratory at Michigan State University. "And it's important to do so from the very first cough. Ignoring a seemingly minor cough can allow it to turn into a major problem."
Of course, you'll rely on your veterinarian to diagnose the cause of your horse's cough and determine the appropriate treatment. But you can gather information yourself that will assist in the process. To help you, Robinson and his MSU colleague and fellow respiratory expert Frederik Derksen, DVM, PhD, explain the seven most common types of equine cough, along with their usual causes and treatments.
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Frequent Dry Coughs
Other signs: Watery nasal discharge, fever, reluctance to eat and/or lethargy
Triggered by exercise? No
Likely cause: Early viral infection. These coughs, which usually come several in a row, stem from irritation in the upper respiratory system. Mucus production is minimal, leading to a drier sound, but that can be difficult to discern. "It can be very hard to distinguish a dry cough from a wet one—that is, one that is associated with moving mucus—in a horse," says Derksen. "Even those of us who research coughs can be hard-pressed to tell the difference, but it's helpful to try."
What to do: Rest the horse two days for every day he coughs and make sure he gets plenty of fresh air. Tell your veterinarian about the situation, though a farm visit may not be necessary. Antibiotics are not effective against viral infections, but careful nursing can help the horse's immune system do its job.
Periodic Wet Cough
Other signs: Copious gray or yellowish nasal discharge, combined with loss of appetite, fever and lethargy
Triggered by exercise? No
Likely cause: Bacterial infection. In horses as in people, bacteria often invade the respiratory system after a viral infection has weakened the body's defenses. "If the horse has a bacterial infection, you're going to see a lot of mucus," says Robinson. This, he adds, is a good thing: Mucus is the immune system's tool for gathering and removing bacteria and damaged tissue from the respiratory tract.
What to do: Call your veterinarian, who will likely make a visit. If he prescribes antibiotics, be sure to finish the entire course even if the horse looks better after only a few doses. Rest the horse twice as long as he was ill, and make sure he gets plenty of fresh air.
Occasional Wet or Dry Cough
Other signs: None currently, but the horse did have a respiratory illness within the past few months.
Triggered by exercise? Sometimes, but not always
Likely cause: Residual effects of the earlier, acute respiratory illness. "The inflammation from an infection, particularly a bad bacterial one, can take weeks or months to resolve," says Derksen. "In that time, the receptors in the horse's airway are going to be hypersensitive, resulting in more frequent coughs in response to less provocation." Eventually, the inflammation subsides and the horse returns to normal.
What to do: To encourage the healing process, give the horse plenty of fresh air and take care to avoid overtaxing him physically. If he is still coughing two months after the original illness resolved, ask your veterinarian to rule out continued infection, chronic respiratory disease or other potential problems.
Repeated Wet Coughs
Other signs: Coughing worsens at predictable times and in certain environments, such as in a stall, at feeding time or when being ridden, and improves when the horse is turned out on pasture.
Triggered by exercise? Sometimes, but not always
Likely cause: Recurrent airway obstruction (RAO), also known as heaves. This condition is an allergic response to airborne antigens, such as dust from bedding or hay. When the antigens are inhaled they trigger bronchospasm that narrows the airways and stimulates copious mucus production. The horse has to work harder to breathe, and coughs are a reaction to the mucus and increased airway reactivity. "The cough may not start immediately after exposure, but within one or two days," says Robinson. Heaves is a chronic condition, meaning the horse will always have a reaction to an antigen and the reactions may get progressively worse as the lungs become more inflamed and sensitive.
What to do: Medications, such as steroids and bronchodilators, can help horses with heaves, says Derksen, but they are best used to treat an acute episode rather than to manage a long-term problem. He adds that the most effective method of minimizing heaves is to put a horse on continuous turnout, wet his hay, and adopt other management measures that reduce exposure to dust and other allergens. "It's not always practical and easy, but ensuring a horse is never exposed to his triggers is really the only way to keep heaves under control," says Robinson. "Once horses are in a dust-free environment they breathe easier and cough less but they are not cured—the problems will return if they are exposed again." Conversely, a small number of horses, mainly in the humid South but also occasionally in the North, develop "pasture heaves" during the spring and summer. Because these horses are allergic to pollens and plant materials associated with pasture, they improve when kept in stalls during these seasons.
Other signs: None. After a few coughs, the horse has no further respiratory disturbances.
Triggered by exercise? Yes
Likely cause: Indeterminate. "This cough is a bit puzzling because it's predictable, not random," says Robinson. "Normally such a cough would be cause for concern, but the horse is perfectly healthy in every other respect." The culprit, he says, is probably accumulation of mucus: "If you endoscopically examined a large number of horses, you'd find that almost all of them have some mucus collected behind the larynx. The cilia of the respiratory tract can move mucus up to the larynx but not past it—the horse must cough to do that. The start of exercise requires a horse to breathe deeper, and perhaps the cough is to clear the mucus through the larynx into the throat. Exercise also transfers fluid from the blood to the lungs, which could trigger cough."
What to do: Nothing. If coughing is limited and never occurs after the first few moments of a ride, there's no cause for alarm or action. "You do want to be careful that you don't 'tune out' a warm-up cough over time," Robinson says. "So you'll be aware if it worsens."
Other signs: None. After the initial four or five coughs, the horse is fine and has a normal workout. Arena coughs are most common during the winter.
Triggered by exercise? Yes
Likely cause: Although this could be easy to dismiss as a warm-up cough, the fact that it occurs only indoors suggests there is more to it. Indoor riding rings are notorious for producing dust that can cause serious respiratory irritation. This dust, combined with airborne particles from hay in a closed-up barn, can cause airway reactivity that at first isn't severe enough to be called heaves but could worsen and become chronic. Deeper coughs at the start of a ride in an indoor arena are your early warning. They are also a warning that the air in the ring and barn is unhealthy for human lungs as well.
What to do: Water your indoor ring before riding or add a footing conditioner to minimize dust. You can also bundle up and ride outside. Also make sure your barn is very well ventilated.
Cough and Strange Body Posture
Other signs: The horse seems distressed and may stand with his neck outstretched or twisted in an odd manner. He may also make retching noises.Triggered by exercise? NoLikely cause: A foreign object lodged in his airways. "We see this more often than you might think," says Derksen. "A horse comes in with a history of an odd, nonresolving cough and you take a look with an endoscope and see a piece of a small tree branch lodged in the larynx or even further down. Removing it completely resolves the problem."What to do: Horses can often dislodge a foreign object with cough themselves, but they may not always. Call your veterinarian if you suspect your horse's coughing is due to something stuck in his throat or trachea. It's not a Red Alert situation, which true esophageal choke would be, but you'll want the horse to be seen within 24 hours for his own comfort.
Many coughs resolve on their own, but others are a warning that something is amiss with your horse's respiratory health. A cough may signal an infection or chronic disease that will worsen if not addressed. That's why it's important to pay close attention when your horse coughs, gather clues and think critically about his situation. His long-term respiratory health depends on it.
The frequency of a cough is an important clue to its cause but can be difficult to determine unless you spend several hours per day with your horse. "We've found through our research that coughs wax and wane over the course of a day," says Frederik Derksen, DVM, PhD, referring to research he has done Ed Robinson, BVetMed, PhD. "And coughing irritates the airways to trigger more even coughs. So you may only hear two coughs between, say, 11:30 and noon. But after you leave the barn, the horse might cough 20 times in the 15 minutes. You may not know how bad the cough is, so it's important to spend time investigating and ask other people who may have heard what you didn't."
Anatomy of a Cough
A cough is initiated when specialized receptors, scattered from the larynx along the entire respiratory tract to the bronchi of the lungs, are stimulated. "Each receptor reacts to a particular irritant such as pollen, dust, mucus or even very cold air. In response, the horse inhales deeply, and the larynx closes shut to trap that air in the respiratory tract. Then, the muscles of the abdomen contract, raising pressure in the horse's chest. The audible cough occurs when the larynx suddenly opens, allowing the pressured air to fly out, taking any irritants with it.
The sensitivity of cough receptors vary from horse to horse, says Robinson. "Some horses can tolerate extremely dusty environments with only one or two coughs while others start up at the slightest provocation." This susceptibility is genetic but is influenced by the current state of inflammation in the horse's lungs. Any inflammation, from an acute disease to a chronic condition, will cause a horse's airway receptors to trigger a cough with less provocation.
"Any degree of inflammation—from acute disease or a chronic condition—leads to hypersensitivity and coughing," explains Fred Derksen, DVM, PhD. "I used the analogy of your finger. If you just tap it against the window ledge, it doesn't hurt all that much. But if had hit it with a hammer the day before and then tap it against the ledge, you're going to feel it more. That's because the initial smack started an acute inflammatory process, making it more sensitive to the later tap."
This article originally appeared in EQUUS 365.