Signs of Equine Asthma

It’s easy to recognize the horse having a flare-up of heaves. That’s the horse that everyone in the barn knows – the one who gets a bad batch of hay and then stands in the stall with nostrils flaring and sides heaving, desperately trying to get air.

It can be a little harder to recognize the horse with IAD, especially because these two diseases are on a continuum of severity, and horses with mild heaves can sometimes look pretty normal. So what does a horse with IAD look like? It depends on what the horse does for a living.

Racehorses – whether they are Thoroughbreds, Quarter Horses, or barrel racers – need every bit of oxygen they can get, so even the smallest amount of respiratory disease can show up as decreased performance without any other distinguishing signs such as a cough, nasal discharge, or visibly abnormal breathing effort. The classic description of a racehorse with IAD is that he ‘quit at the ¾ mark.’ The Kentucky Derby horse that loses by a length – which seems like a huge amount in a race – is only about 0.15 seconds slower than the horse ahead of him, and he may well have lost because he had IAD. Bottom line – IAD shows up in young racehorses and can be very difficult to diagnose without advanced techniques. Polo ponies also live on the oxygen edge – at least they do if they are high goal ponies. During a 7-minute chukka, polo ponies can cover 3 miles at a gallop going up to 30 miles per hour.

As with racehorses, you may never hear them cough, and it’s unlikely that they’ll have nasal discharge – but they might get ridden off as you gallop with an opponent toward the ball. High level event horses, competitive endurance horses, and jumpers might also just have poor performance without having other identifiable signs of respiratory impairment. Occasionally, however, the rider or trainer may note that the horse takes longer for the respiratory rate to return to normal after peak exercise, or that the horse ‘blows’ more than other horses after exercise.

Most of our equine athletes, however, don’t live on the edge. Horses have been blessed with an extraordinarily large respiratory reserve. If you’ve ever wondered why we race horses and not cattle – who after all, are about the same size as horses – it’s probably because horse lungs are almost twice the size of cattle lungs. This means that until horses are at peak exercise, they probably don’t need all the oxygen that their lungs can deliver. In consequence, we tend not to notice the beginning stages of IAD. IAD can go undetected in even a high level dressage horse or hunter/jumper or reining horse for a long time. It isn’t until these athletes start to cough or have a noticeable nasal discharge that we look for evidence of respiratory disease. Many riders will describe the horse that practically pulls them out of the saddle with a cough at the beginning of a ride. Unfortunately, because IAD is so common, many people think it is normal for a horse to cough at the beginning of a ride. Coughing is common, but that doesn’t mean that it is normal. Coughing is a sign that all is not well with the respiratory system, and the most common cause in horses is IAD. Earlier signs, however, can be noted by an astute rider or trainer – these can include trouble getting a horse on the bit or even noticing that a horse is making a respiratory noise when he’s on the bit, taking down a rail, swapping leads, or just a generalized ‘lack of brilliance’. All of these non-specific signs can be a warning that something is wrong with the horse’s respiratory system.

Media1  (click here for a video of a lovely dressage horse with a cough)

Although heaves is classically a disease of stabled horses, we find that many IAD horses in the New England area have exacerbations of disease in the late spring and summer. They tend to have the most severe signs when it is hot and moist. Many horses also have worse signs with the advent of pollen season, especially when their pastures are surrounded by evergreens. Signs are also often worse when indoor arenas become dusty or barn management practices increase the dust in the air.