Coughing in horses: when it is not only the lungs

Two or three coughs as he moves into trot, then it is gone. A few weeks later he coughs while being groomed too. And in the yard someone says the sentence I hear most often: “Lots of them have that here.” It is even true. Only it is not reassurance, it is the actual finding.

I am rarely called about a cough. I am called about a drop in performance, about “he somehow doesn’t want to any more”, about a horse that suddenly stops out hacking. And when I ask, it almost always turns out: it had been coughing before. Months before. Only nobody read that as illness.

That is no reproach. Coughing is so widespread in stables that it passes as a normal noise — like snorting or pawing. That is exactly where the problem lies.

A cough is a message, not a disease

Coughing is a protective reflex. It clears away what has no business being in the airways. A horse that coughs is therefore not telling you: “I have a cough.” It is telling you: “There is something in my airways that does not belong there, and I cannot get rid of it.”

That is why “what do I give for the cough?” is the wrong first question. It is understandable, and sometimes an expectorant makes sense. But it aims at the noise, not at the reason. It is the same mistake in thinking I describe in my article on dog allergies : we treat what we hear and see, and overlook what causes it.

And one more thing belongs at the start, because almost every horse person has been told it once: A horse does not cough itself clear. A healthy horse does not cough. Not moving into trot, not getting up, not in the morning. Once you really take that sentence in, you hear your own yard differently.

Why the cough has a different name today

If you have been around horses for a while you know COB, RAO, COPD or simply “broken wind”. These names are professionally out of date. In 2016 an international working group brought them together in a joint guideline under one term: equine asthma. The Swiss Institute of Equine Medicine in Bern was part of it — so the subject is not only being pushed forward elsewhere.

This renaming is no quibble over words. It says three things that matter day to day:

• It is a spectrum, not a switch. Between “coughs twice moving into trot” and “stands in the box with a heave line” lie many stages — and the same disease.
• It is inflammation, not dirt. The airways over-react to something inhaled. That cannot be rinsed out or coughed out.
• The mild form is the important one. At that stage almost everything is still possible. It is also the one most reliably overlooked, because the horse otherwise looks healthy.

The most common lung disease of the adult horse

“Lots of them have that here” is not reassurance, it is a statistic. In a survey of horse owners in the United Kingdom, around 14 per cent of horses showed signs consistent with chronic airway disease (Hotchkiss et al., Equine Veterinary Journal 2007, volume 39, p. 301). For the milder forms the estimates are considerably higher, because they are barely noticeable without examining the lungs.

Put differently: in a yard of fourteen horses at least one is statistically affected — and several more are on their way there. That coughing in a yard soundsnormal is not because it isnormal. It is only common.

What your horse breathes 23 hours a day

Here comes the part that matters most to me. When we think of airways we think of the lungs — of the organ, the horse, the treatment. But the decisive factor is not inside the horse at all. It is all around it.

Work out how much time your horse actually spends in its box. For many it is twenty hours or more. During that time it breathes the air of that box — with everything floating in it: spores from the hay, dust from the bedding, ammonia from urine below the top layer. And because the haynet hangs at head height, the nose sits for hours exactly where the concentration is highest.

Two findings from the same series of studies at the University of Edinburgh struck me at the time as sobering and helpful at once:

• Soaking hay works, and immediately. Fine dust in the horse’s breathing zone dropped markedly when the hay was soaked before feeding. Hours of soaking gave no extra benefit over a short soak — so it need not be laborious, only regular.
• Your box does not end at the box wall. Where walls are open and the air space is shared, fine dust in the neighbouring box rose ninefoldwhen straw bedding and dry hay were used next door. Conversely it fell measurably as soon as the neighbouring box was changed.

The second point is the uncomfortable one. It means: you can do everything right for your horse and still achieve little if half the yard is bedded on straw. This is not an invitation to argue in the aisle — but it explains why some changes achieve nothing, and it turns an individual question into a yard question.

Why the surroundings can do more than the medicine

I am a veterinarian. I do not demonise medication, and for a horse struggling to breathe, corticosteroids are not a question of worldview but of necessity. What impresses me about the evidence nonetheless is the ranking.

In horses with severe equine asthma, researchers compared what happens when you either change the environment consistently over months or give inhaled corticosteroids. Both improve the symptoms. But: the inflammation in the lungs normalised only where the exposure was removed — and the pathologically thickened airway muscle receded markedly only in that group (summarised in a review of environmental management, Animals 2024). The medicine takes away the horse’s distress. The environment takes away its cause.

For everyday life that means an unspectacular order of priorities, which I almost always recommend in this form:

1. Time outside, as much as at all possible. The least dusty air is out in the field. For many horses more turnout is the single most effective measure — and the cheapest.
2. Away from dry hay. Soak or steam it, every ration. Hay from the ground rather than from a high-hanging net, so that secretions can drain and the nose is not stuck in dust for hours.
3. Check the bedding. Low-dust shavings instead of straw, and mucking out often enough that no ammonia builds up below the surface. Your own nose is a usable measuring device here.
4. Do not work in the stable while the horses are inside. Sweeping, bedding down and hanging hay stir up exactly what you are trying to avoid.
5. Only then talk about medication. What else makes sense is decided by the examination — not by advice from the aisle.

When a cough needs a vet immediately

A chronic cough can wait for an appointment next week. Some things cannot. Get it checked immediatelyif any of these come with it:

• Fever, listlessness or a horse that will not eat.
• Yellowish, purulent or bloody nasal discharge, especially on one side.
• Laboured breathing at rest: flared nostrils, visibly working abdominal muscles, a heave line along the rib cage.
• Coughing while eating, or food coming out of the nose — that can be a swallowing disorder and is an emergency in its own right.
• A sudden collapse in performance, or a cough that gets markedly worse within days.

And because yards tend to wait: fever with a cough is no case for herbal syrup. That is the moment for a phone call, on the same day.

Where else I look — and which part of that is experience

Everything so far is in the textbooks. Now comes the part that belongs to my work, and I say expressly what kind of thing it is: What follows is my observation from thirty years, not a body of research. Anyone selling you the two as the same thing is doing you no favour.

With a coughing horse I always also look at how it stands. Breathing is movement — ribs, diaphragm, the whole trunk. Horses that work against thick mucus for months become tight in the chest, and that tension does not disappear by itself when the air improves. I look at feeding and supply, because a body expected to repair needs material for it. And I look at what changed in the horse’s life before the coughing began: a new yard, a new neighbour, a different herd, less rest.

This replaces no clean-up of the environment — it comes after it. But it often explains why two horses in the same row of boxes react differently. More on how I understand this double view and where it ends is in Holistic veterinary medicine: when it makes sense.

The first step costs nothing

If you do one thing after this article, let it be this: take two weeks and write down when your horse coughs. In the box in the morning or only in the arena? In dry cold or in damp warmth? In the first five minutes of work or throughout? Out in the field too?

That list is worth more than it looks. It turns “he coughs sometimes” into a pattern — and a pattern points somewhere. Coughing only indoors points elsewhere than coughing only in spring out in the field. Your vet can do more with those two weeks than with any suspicion, and while writing it down you hear things you previously missed.

Because that is the genuinely good thing about this disease: to a large extent it is home-made. And what is home-made can be changed again.