When considering your older horse's respiratory health, first take a look at the numbers; The average horse takes about 17 breaths per minute. By the time he reaches age 20, your horse will have inhaled and exhaled approximately 178,704,000 times. That's a lot of breathing.
Fortunately, lungs don't wear out. In fact, aging itself has little effect on the equine airway. Respiratory conditions are just as likely to develop in younger horses as in their older herdmates. But a chronic respiratory problem may worsen with the passage of time, particularly if it hasn't been managed effectively. And if an older horse develops an acute respiratory illness---pneumonia, for example---it may take him longer to recover than if he were younger.
For these reasons, it's important to monitor your horse's respiratory health as he grows older. Indeed, if you are as mindful of his lungs as you are of his legs, teeth, eyes and other organs, you'll increase the likelihood that he will con?tinue to breathe easily well into old age.
The Effects of Time
Recurrent airway obstruction (RAO, also known as heaves) is age-related only in the sense that it is rare in horses under age 5. "We don't see it in very young horses," says Frederik Derksen, DVM, PhD, of Michigan State University. "We don't know exactly why it takes some time to show up, but it's most likely related to the development of the immune system."
Heaves is caused by airborne irritants in the horse's environment. Inhaled dust, molds and other particles travel to the deepest reaches of the lungs, triggering an allergic inflammatory response that leads to excess mucous production and a narrowing of the airways. These changes, in turn, make it harder for a horse to breathe, particularly to exhale.
Other than becoming excessively winded after exercise, a horse with mild heaves may seem normal. In contrast, a horse with a severe case may struggle to breathe even when simply standing in his stall. The sustained effort required to exhale can even lead to abnormal muscle development around his diaphragm, leaving a visible "heaves line" along his flank.
Though heaves is rare in young horses, advancing age does not necessarily increase the risk of the condition. A horse who does not have a genetic makeup that leaves him susceptible to heaves probably won't develop the condition as he grows old, says Derksen: "We have a herd of 30 older research horses here at Michigan State. They've been here between 10 and 15 years. About half have RAO. The horses who do not have it never develop it---no matter how long we leave them in a dusty barn. The ones who do have it, however, will consistently develop heaves when exposed to irritants---sometimes within a few hours. This tells us that there is a genetic predisposition to the condition and if a horse exposed to allergens doesn't have heaves by the time he's mature, chances are he's not going to suddenly develop it."
Nor does the management of heaves change with age: The first step is always reducing the horse's exposure to dust as much as possible. "Turning the horse out, wetting hay, feeding hay cubes---all of these work when a horse is 20 as well as they did when he was 10," says Derksen.
On the other hand, says Derksen, additional measures may be required if an aging horse's heaves haven't been managed effectively over the years. "If heaves is left unchecked for a long time, the lungs will eventually remodel and develop scarring," he says. "When you have these types of changes, it's harder for the lungs to recover. That's when you may need medications like bronchodilators and corticosteroids in addition to the environmental changes."
In cases where medication is required for heaves, the horse's age can play a role in treatment decisions. "Many older horses have Cushing's syndrome," says Derksen, "and, as a result, can be more sensitive to corticosteroids. To avoid the risk of laminitis, veterinarians will use these drugs very judiciously. They'll want to make sure the Cushing's is well under control."
Protection from Infection
Respiratory infections are not a big concern for most older horses simply because their working days are behind them. "These infections, like pleuropneumonia, tend to occur when horses are traveling and competing," explains Derksen. "The stress of being on the road and the athletic efforts, combined with being exposed to new horses and germs, can all lead to respiratory illness." Older horses, however, tend to travel and compete less. "It's a perk of retirement for older horses," he says. "They aren't being shipped all over and exposed to as many new germs. You'll regularly hear of elderly people dying of pneumonia, but that would be a very unusual way for an old horse to go."
When an older horse does pick up a respiratory bug, however, the resulting illness may be more severe and take longer to resolve than it would have when he was younger. "The immune system of an older horse may be less effective in fighting off disease," says Derksen. "As a result, an older horse may get sicker and be sicker longer." While a younger horse may muddle through an infection with standard medications and a bit of rest, an old horse may need more powerful antibiotics and intensive supportive care to deal with a bout of serious respiratory illness.
In addition, the effects of an infection may linger. "If there is any unresolved airway inflammation in the lungs, cold air or a high airflow rate across it can trigger a cough," says Derksen. An older horse may seem completely recovered as he stands around the field but start coughing if he picks up a fast trot to come in for dinner. This can go on for weeks or months until the residual inflammation is resolved.
Of course, if your older horse is still traveling, competing and meeting new horses, protect him from respiratory infections as you would a younger horse, says Derksen. "That means keep?ing up with his vaccinations, leaving him tied loosely in the trailer so he can drop his head to cough and clear his airway, not letting him drink from communal water troughs and preventing him from touching noses with every new horse he meets."
Horses enter their golden years with the same or fewer respiratory risks they had as youngsters. They don't require different or specialized care to keep their lungs in good shape. If you've managed your horse wisely before, you'll be in a good position to continue maintaining the health of his airways.
A number of drugs are useful in the treatment of equine respiratory disorders:
Antihistamines:These medications act by reducing the immune system's reaction to irritants, reducing airway inflammation. Although antihistamines help control allergy-related respiratory disease in people, they are effective in only about 10 percent of horses. They are, however, extremely safe, so your veterinarian may give them a try in case your horse is one of the few who can benefit.
Corticosteroids:These powerful medications control the inflammatory response in the horse's lungs. Dexamethasone has been shown to be particularly effective at improving lung function, producing dramatic results within three days.
Corticosteroids can be given orally, but the preferred method of administration is through an aerosolizing mask, which delivers medication directly where it is needed and reduces the potential for systemic side effects. Because of the associated risk of laminitis, corticosteroids are given cautiously and only after environmental changes have not produced results.
Bronchodilators:These drugs, such as clenbuterol and albuterol, relax smooth airway muscles, "opening" the airways. Various forms are administered orally, intravenously or inhaled through an aerosolizing mask or device. Bronchodilators are often given to open the airways 15 minutes before inhaled corticosteroids are administered, increasing the distance they can travel into the lungs and, therefore, their efficacy.
Antibiotics:In cases of bacterial respiratory infections, a veterinarian will prescribe an antibiotic effective against the causal organisms. She may?also prescribe antibiotics in cases of viral infections to prevent opportunistic bacteria from flourishing while the horse's immune system is compromised.
Note:Nonsteroidal anti-inflammatory drugs (NSAIDs), such as phenylbutazone and Banamine, aren't used in the treatment of respiratory disease because they inhibit a prostaglandin that protects the airways against bronchospasm.
Poor quality, moldy hay is the obvious culprit when it comes to causing equine respiratory problems, but there are many more sources of airway irritants lurking around the barn:
- Riding rings. If you leave the arena with a visible layer of dust on your body, the air in that space is unhealthy for you and your horse. Use water or footing additives to reduce arena dust.
- Haylofts. Tossing flakes into stalls from an overhead loft is convenient, but with each meal, a storm of dust will rain down on the horse. Toss hay only when the stalls are empty, or move hay to a lower level and place it neatly in stalls.
- Leaf blowers. These machines stir up dangerous amounts of dirt and dust, blowing it directly to the level of horses' noses, where it can hang in the air for hours. Never use a leaf blower when horses are in the barn. Instead, sweep aisleways when they are out in the fields.
- Pelleted feeds. A scoopful of feed dumped into a feed bucket can create a tiny cloud of dust as it lands. This would be a minor issue if horses didn't wait eagerly with their noses in their buckets as meals are delivered. Scoop out grain and let it settle before giving horses access. Better yet, pour the grain and then spritz it with a bit of water, letting the horse eat it while it's still damp.
Bedding. Poor quality, musty straw and sawdust can irritate sensitive airways. A good choice of bedding for a heavey horse is clean, large wood shavings.