The lungs and declining performance

Just because your horse is not coughing does not mean that there is no problem! Now that more horses are kept together inside, respiratory problems will pick up.

This month I would like to inform you about the problems of the airways of horses. Of course, if a horse is coughing and has a runny nose, it is normal the think about an infection of the throat or bronchi or in other words, the respiratory tract. But next to that problems in this area are one of the most underestimated causes of declining performance. Currently respiratory problems are one of the biggest causes of economic loss in the horse industry. In racing and trotting respiratory afflictions account for more loss of use than any other medical problem.

An upside down tree
The upper airways and lungs can be looked at like an upside down tree with the trachea as the trunk, the branches the bronchi and the leaves, the alveoli. In the alveoli oxygen is taken in and carbon dioxide is released. The wall of these alveoli is covered with very tinny finger-like projections. The horse is naturally a flight animal and therefore provided with an enormous lung capacity so it can run fast and for long distances. A horse in rest uses 60 litres of air in a minute, in gallop this is up to 2000 litres!
This reserve capacity is even in competitive performance often not totally used. Problems can arise in an early stage however, when the lungs do not function to the maximum because of damage occurring in the past which has affected the ability to use the inhaled oxygen efficiently. A good reason so to avoid lung damage in a (young) horse so.

Coughing
On itself is coughing a good reaction of the body to get rid of a problem. The reflex of coughing should therefore not be suppressed initially. Of course, if the coughing gets out of hand specific treatment has to be started.

The lungs under attack
There are several possible causes of the start of respiratory problems;
Infections;
infections starts normally by inhaling a virus. The virus penetrates the tissue and the horse can develop a fever. Very often though, this is not noticed. Depending on the virus it will normally take a couple of days to multiply and to actually cause damage to the bronchi. Bacteria can grow excessively in these damaged bronchi. The finger-like projections get damaged, the tissue gets inflamed and more tenacious mucus is produced. By this time the horse can show nasal discharge and will start to cough. If this situation persists for a longer period of time (more than 5 days) the tissue in the lungs will get more inflamed. This will lead to the swelling of the wall of the bronchi and constriction of the muscles in the lungs. Result is a narrow tube which will give problems with the oxygen intake.
Inhaling of allergens
Allergens are substances which causes inappropriate response by the immune system of the horse. Typical allergens are found in some plants and mould from hay and straw. The body reacts to these allergens with its own defence mechanism. In horses which have a (light) allergy the body will overshoot the mark so far as the reaction is so great it does more harm than good. This reaction will cause damage to the lung tissue.

Permanent damage
Breathing takes more energy when an infection or allergy occurs as there is lesser natural elasticity of the lungs. When breathing in the air is taken in with great power. As the exit is partially blocked because of the swelling air can get trapped in the lungs. In this situation the alveoli deep in the lungs can burst. The body cannot replace this and permanent damage is a fact (lung emphysema). Horses with a serious form are called broken winded. This may happen much faster if a horse has to perform while affected.

Identifying problems
Horse keepers should keep an eye out for symptoms of respiratory problems. Sometimes this is very obvious but not always. A dry cough at the start of riding could be the first indication of a developing allergy, for instance. If any doubt please don’t hesitate to call a vet. Clinical examination should consist of complete check in rest, auscultation of the lungs before and after exercise. Sadly enough there are a lot of problems possible without clear symptoms form the outside. Looking into the lungs (bronchoscope examination) is a very quick, cheap and safe way of getting a lot more information from the inside. To get a complete picture of the lungs it is possible to do a so called Lungwash. A small amount of water is brought into the lungs and immediately sucked back into a test tube. This fluid will show all the cells in the lung contents. Especially in cases where the other examinations give no satisfactory results this test can be of great value in getting to proper diagnoses.
Horse with loss of performance, but with no diagnosis in motion and bloods, can be great patients for the lungwash as it will often give an explanation for long term problems.

Clean air
Looking at the large amounts of oxygen the horse is inhaling it is important that this air is as clean as possible. Unfortunately this is often not the case. A lot of attention has to be paid to the environment in which the horse is kept inside. Obvious triggers of respiratory problems have to be avoided.

• Always enough ventilation in the stable. Ventilation is clearly something else than draft. If a person enters a stable it should smell fresh without a detectable draft in the stable.
• Avoid the stock of hay and straw on top of the stables. In time all the dust and mould will fall down into the stable and thus put the horse under a high allergy risk.
• Ammonia from the urine is one of the most aggressive substances for the respiratory tract of the horse. Keep the bedding fresh and dry.
• Sensitive horses should not be stabled on straw and fed equine haylage instead of hay. Wetting the hay is often an problem on itself. To really get rid of the moulds etc the hays has to be made very wet (lying under water for 30 minutes) and by doing this the taste and some useful elements form the hay are washed out.
• Feed hay/haylage on the ground. If a horse graps hay out of a net or rack the dust will directly fall into its nose.

Treatments
There are several possibilities for treatment of respiratory problems. Practically the horse keeper needs to limit the amount of dust around, not using straw, feed equine haylage and ensuring good stable ventilation (or keep the horse outside).
Medication can be used to reduce the build up of mucus and inflammation and to dilate the airways. Traditionally this is most often done by oral administration or injections. In severe cases or in chronic patients this will create a lot of practical problems. Recently I have been involved in the new generation of sound active nebulisers (equineb®, romedic)  and this seems to be very promising. The different types of medicine that can be used are far more modern and effective than the traditional drugs. There is no need for (twice) daily injections or refusing food anymore. Personally I find the biggest advantage of the inhalation of medicine the dosage of the drugs. In general the dosage is about one-tenth of the dosage needed with oral and/or inject able medicine. Much more direct and less medicine load on the body.

Of course prevention is better than treatment. As we are still not able to treat viruses (antibiotics will only treat the bacteria’s), vaccination is a factor in reducing the risks and costs of respiratory problems. Most commonly vaccination is carried out for the prevention of influenza. Another possibility is the vaccination against herpes viruses (rhinopneumonia). Worldwide some discussion is going on about the effectiveness of these vaccines. I have personally seen massive reductions of problems on stud farms and riding stables that did decide to vaccinate. This vaccine has to be given twice a year to be any effective.

Never take any risks with the lungs of your horse and always make sure treatment is carried out based on the correct diagnosis, is in time and with effective medication.

Dr. Henk Offereins
Kenmare Veterinary Centre, Kerry
www.kenmarevc.ie