Healthy Stables – Respiratory

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by Richard Knight BVetMed MRCVS on behalf of Peter Fenton Equine Vets

With winter fast approaching (if not already here in the North West!) it is time once again to prepare your stable to keep your horse happy over the next few damp, cold months.

There is a lot more to consider though, than simply emptying a couple of bags of shavings on top of some rubber mats, preparing large numbers of feed buckets and trying not to grumble as muck out yet again!

This article will address some of the changes you can make to you horses’ stable environment to help prevent, or treat, commonly encountered respiratory problems though the winter months.

Horses have huge lungs, designed over millennia to allow increased athletic ability through greater airflow and oxygen exchange.

Horses are “Obligate Nasal Breathers” meaning they only breathe through their noses.

As the horse inhales, the Diaphragm (a muscle in between the thorax and abdomen) and Intercostal Muscles (found between the ribs) contract. These actions increase the internal volume of the thorax and draw air in through the nose.

This air then moves into the lungs through the Trachea (windpipe) and then Bronchi and Bronchioles.

The Bronchi are smaller airways which extend from the trachea into each lung lobe, they have rings of cartilage which surround them which prevent them from collapsing as large volumes of air move through them.

The Bronchioles are tiny airways, which eventually lead to the Alveoli (or air sacs) in which oxygen is exchanged for carbon-dioxide.

The Bronchioles and Alveoli do not have cartilage rings and can collapse or become obstructed in certain diseases.

As the lungs are a major site of interaction between the horse and their environment, with large numbers of potentially harmful bacteria and particles being breathed in every day.

To try and prevent infections from occurring the lungs have developed a highly specialised set of defences to minimise the chance of foreign material reaching the tiny alveoli and bronchioles.

These defences include;

  • Tiny hair-like Cilia, which project from the walls of the upper respiratory tract. These continually move in a wave-like fashion to move inhaled particles up, out of the lungs, to the throat where they are coughed up, or swallowed.
  • Mucous producing cells, which secrete a sticky layer of mucous to trap particles, this mucous is then moved up out of the lungs by the Cilia.

Despite these defences respiratory diseases in horses are relatively common, ranging from dust allergies to viruses such as Influenza.

One of the most common diseases to affect horses is Recurrent Airway Obstruction (RAO). RAO occurs when horses develop an allergy to an inhaled particle. These particles are frequently pollens, dusts or mould spores.

Once inhaled the immune system detects these particles and responds excessively, causing the muscle in the walls of the small bronchioles to constrict, reducing their diameter and dramatically increasing the resistance to airflow in the lungs. This means that affected horses need to breathe much harder than normal, giving the disease it’s alternative name of “Heaves”.

As the disease process worsens the lungs become inflamed, producing excessive amounts of mucous and further restricting the flow of air. This mucous can be seen as a clear/white nasal discharge.

This build-up of mucous needs to be removed from the lungs, which is why almost all horses with RAO will develop a cough, either when exposed to the causative dusty environment or when they are exercised.

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The initial signs of RAO are sometimes very subtle. Normal horses will cough occasionally, much the same as we humans will all occasionally cough, but a regular cough is the one to watch out for!

If the horse continues to be exposed to the causative irritating particles their breathing will become more laboured and their ability to exercise may be reduced. Horses who are struggling to breathe will begin to use their abdominal muscles for respiration in addition to the Diaphragm and Intercostal muscles. While this can be quite difficult to spot, long periods of increased breathing effort will lead to over-development of the abdominal muscles, and the appearance of a “Heave Line” along the flank of the horse.

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In severely affected horses the respiratory distress can be severe. Horses will wheeze audibly, stand with their elbows out (to increase the volume of the chest), flare their nostril and display marked abdominal movement.

These horses require urgent veterinary attention to reverse to inflammation and dilate their constricted airways.

While the worst case scenario above is sometimes unavoidable, there are numerous actions that you, as owners can take to reduce the likelihood of such an event occurring.

When bringing your horses in for the winter carefully observe them for any evidence of a regular cough or excess nasal discharge. Allergies can develop at any time, so just because your horse’ didn’t suffer last winter it doesn’t mean they won’t this time!

If you are concerned in any way, give your vet a ring!! They will be happy to take any questions you may have, as well as give advice of how best to approach the situation.

If you suspect your horse may be susceptible to RAO then management of their turnout and stable is the key!

RAO can be improved, or even completely prevented, by removing the horse from the allergen they react to. Obviously the best place for this is the middle of their field, where the air is free from such particles.

Some horses however will have their RAO caused by pollen grains, a disease called Summer Associated RAO. These horses will need to be kept in during the day when the pollen count is higher, but they can be turned out at night. While this is the opposite of traditional RAO the theory is just the same, removing the horse from causative allergen.

On most yards all-year-round turnout is normally difficult to arrange so a compromise between turnout and stable-management needs to be made.

Stables are fairly horrid places for the respiratory system.

They are quite commonly dusty, dark and sometimes damp buildings, often with inadequate airflow.

Stables should always be well ventilated, with either windows or doorways providing a constant supply of fresh, clean air. Often stable buildings house many horses, and while those towards the ends of the barn have quite good ventilation, those in the middle have quite stagnant air.

If you think that your horse suffers from RAO, in a stable with bad ventilation it is probably worth a quick ask around to see if you can move to a better box, or if the building can be modified to improve the airflow.

Bedding is a big contributor to the stable environment as it can be a huge source of dust and mould spores. While straw is cheap, it is often the worse bedding possible for horses with respiratory disease. It is true that very good straw can be dust free, but this is often not what is available on farm.

Bedding materials such as rubber matting, shavings (which can be specifically “Dust Extracted”), recycled paper or cardboard are far better for these horses as they contain far fewer dust particles.

It is important to note that if your horse suffers badly from RAO, you will need to ensure that the stables adjacent to theirs are also as dust-free as possible. Particles can travel a long way in a barn environment and all of your hard work can be undone if the overall environment is still dusty.

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Stables should be kept free of muck and urine. If left on the floor the urine will decompose, producing ammonia. This is a gas which is very irritating to both the eyes and lungs, and the constant dampness will promote the growth of funguses and moulds.

Horses should not be present when their bed is mucked out as this will quickly create a dusty environment, so tie them up outside until the dust has settled.

All hay contains some mould spores which become airbourne as horses pull at their net. Soaking hay for a minimum of 30 minutes will prevent these spores from being released, but the hay must still be damp when fed!

It is also best if hay and bedding are not stored in the same place as your horse is stabled, so use a separate barn for these.

Feed buckets are another very common source of mould spores, and should be washed regularly with clean water and a mild disinfectant. It is also important that you store your hard feeds in a dry environment. If you pour your bags of hard feed into bins or storage containers these should be regularly completely emptied and cleaned as they are a breeding ground for dust-mites and various moulds.

As you can see there are large number of small changes that can be made to help improve your horses’ stable environment and minimise the frequency of RAO attacks. While not all of these changes may be possible on your farm, the higher the number you can make the better your horse will be for it!

If you still have some questions about RAO or how to improve your stable environment, then give your veterinary surgeon a ring!

Author: Features Editor

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