The Equine Respiratory system and problem associated with stable kept horses - Like several other bodily systems, the respiratory system has a primary function and several other subsidiary but nonetheless important functions. The primary function is to get oxygen into the blood. Without oxygen, all bodily heat production and activity will cease. The subsidiary functions can be listed as follows:

1. THE UPPER RESPIRATORY TRACT
This lies within the head and neck and provides, in simple terms, the 'pipework' to convey air to and from the lower respiratory tract; this 'pipework' is an arrangement of passages lined with a delicate membrane well-supplied with blood vessels. Some change occurs here in the humidity of the breathed air and heat exchange occurs too e.g. cold air which is breathed in in winter is warmed before it reaches the lungs by passing via the nostrils, nasal cavities, pharynx, larynx and the trachea (windpipe).

2. THE LOWER RESPIRATORY TRACT
This lies within the chest. The trachea divides into the two main stem bronchi at the entrance to the chest cavity - one branch going to each lung. From this point, each bronchus divides and subdivides into bronchioles which ultimately end as alveolar sacs in the lungs; these in turn are subdivided into many little alveoli (which resemble bunches of small grapes) in order to give maximum surface area for oxygen absorption. Within the alveoli, air and blood are exceedingly close together due to the fine branching of blood vessels within these lung structures.

Oxygen is able to diffuse through the fine layer of cells from the air into the blood, and carbon dioxide and water move in the opposite direction. Deoxygenated air is then exhaled back to the upper respiratory tract and eventually out via the nostrils. The deoxygenated blood supply is delivered from the heart via the pulmonary artery which progressively divides in the lungs until gaseous exchange with the blood occurs at the alveoli; the small blood vessels then progressively rejoin until oxygenated blood is delivered to the heart by the pulmonary vein.

The lungs are two large elastic organs which completely fill the chest cavity (apart from the cavity occupied by the heart) between the ribcage and the diaphragm. The lungs are surrounded by the pleura, a smooth. slippery membrane that prevents friction whilst the lungs expand and contract. The basic function of the lungs is to absorb oxygen from inhaled air and excrete carbon dioxide in exhaled air. Air is drawn into the lungs by muscular expansion of the ribcage and is expelled by elastic recoil of the ribcage. When the diaphragm muscles contract, the size of the chest cavity increases so unimpeded diaphragm movement is important if deeper breathing is to be possible. However, if the stomach and intestines are full, the movement of the diaphragm is limited which is why racehorses and event horses have no hay or bulky food and only a small feed on the morning of race day or the cross- country.

The horse at rest has a respiratory rate of 8 to 16 breaths per minute. After prolonged rapid exertion this rate may increase to 120 breaths per minute . Recent research into exercising horses has shown that the functional efficiency of the respiratory system may be a limiting factor of performance even in healthy animals. Any reduction in functional efficiency or capacity may significantly reduce aerobic metabolism in exercising horses.

STABLE RELATED DISORDERS OF THE EQUINE RESPIRATORY SYSTEM
Respiratory disorders generally impair gaseous exchange during exercise and limit performance primarily by increasing the airways' resistance to airflow. There are a variety of disorders associated with both the upper and lower respiratory tracts and some of these can be attributed directly to causes related to stabling of equines. Increased airway resistance, particularly of the lower airway, can be caused by reaction to biological agents (viruses, bacteria, fungi), chemical agents (ammonia, hydrogen sulphide, ozone), or physical irritants such as dust or pollen. Resistance is increased by a combination of bronchospasm, oedema (increased fluid accumulation), hypersecretion (increased fluid production) and decreased airway clearance.

A major factor affecting the resistance to airflow is smooth-muscle contraction or relaxation which produces changes in the diameter of the airways. When certain materials such as dust or pollens are inhaled, irritant receptors are triggered which in turn cause bronchoconstriction and increased airflow resistance. By far the most frequent causes of chronic loss of respiratory function are a result of air contamination by the biological, chemical or physical pollutants outlined above. The effect of some of these is enhanced where horses are stabled in confined spaces for significant periods of time each day and where ventilation is inadequate.

The classic 'stable allergy' respiratory disorder - Chronic Obstructive Pulmonary Disease (C.O.P.D.)
Also sometimes known as equine asthma. As the name implies, it is a chronic disease which develops over a relatively long period of time and is the result of a developing hypersensitivity (allergy) to certain air contaminants (allergens). Usually, C.O.P.D. is more of a problem in winter when horses are stabled for long periods - the problem in this case being mainly a hypersensitivity to the fungal spores found in hay and straw. The problem can be further exacerbated by both high levels of ammonia in stables (where urine-soaked bedding is allowed to accumulate rather than being removed daily) and by poor atmospheric air quality e.g. when air is heavily polluted by oxides of nitrogen, sulphur and carbon, ozone and suspended solid particulates such as soot, dust and smoke. These are typically associated with the still conditions of winter anticyclones when there is virtually no dispersal or removal of the pollution.

It has recently been recognised, however, that occasionally the allergic response can occur in summer when horses are out at grass; here the allergen is probably one or more types of pollen. This 'hay fever' type asthma can come on as acute episodes very similar to human asthma. Recently, hypersensitivity to the pollen of oilseed rape has been implicated as the allergen in a particularly severe form of equine asthma known as Summer Pasture Associated Obstructive Pulmonary Disease (S.P.A.O.P.D.). The symptoms of any form of Obstructive Pulmonary Disease are frequent coughing which is often spasmodic. The coughs sound long, deep and hollow. There may be considerable respiratory distress. At the end of exhalation a line may be seen stretching from the stifle along the line of the belly where there is a double lift (or heave) to complete expiration; this line is known as the heave line and develops because the abdominal muscles are having to do more work to compensate for some loss of lung elasticity, function and volume as a result of the allergic reaction. Breathing is laboured and wheezy, nostrils are flared in an attempt to draw in more air and even the slightest exertion brings the horse to a wheezing, coughing stop.

There is no permanent 'cure' for C.O.P.D. - type afflictions but there are a variety of measures, both natural and pharmaceutical, to help offset or control the detrimental effects. Conventional pharmaceuticals may not be suitable for long-term use for management of the problem because of possible side effects or contra-indications or because they contain prohibited substances under the rules of the Jockey Club, B.H.S., B.S.J.A.or F.E.I.. For these reasons, many horse owners are turning to alternative therapies to help manage and maintain healthy respiratory function.

The likelihood of recurrence can be further reduced by good management of the stable environment. If the coughing is allowed to continue, it may damage the delicate tissues in the lungs causing emphysema. Stable management is based on a regime of minimum dust and fungal spores.

Herbalism can provide an alternative natural means of managing and maintaining healthy respiratory function by using Phytotherapeutic products based on plants traditionally known for their soothing and cleansing properties in relation to the respiratory tract such as eucalyptus, liquorice and garlic.

These and other plants have long been recognised for their ability to reduce friction in the airways as well as reducing viscosity of inflammatory mucus produced deep in lung tissue. They may also possess properties whereby inappropriate inflammatory allergic response is reduced, thereby reducing the generation of harmful free-radicals by specialised soft tissue cells such as Mast cells. This in turn helps to limit lung tissue damage and consequent performance-limiting factors such as reduced gaseous exchange and decreasing lung capacity.

Some plant materials have been shown to contain essential nutrients required for the maintenance and repair of good elastic lung tissue, supplying the nutrients necessary for the specialised biosynthesis of elastic collagen. THERE'S SOMETHING IN THE AIR! THE GREAT VENTILATION DEBATE. Over the past thirty years or so, 'open' ventilation of stables has been considered essential to the horse's well being but now some scientists and veterinary surgeons believe that horses kept in such conditions have become more prone to infection.

Changing uses of horses since last century have produced new attitudes to stable management. Many modern stables are inferior architecturally to those built last century when all horses were working horses. Modern stabling has more emphasis on fixed open vents, free air flow and fluctuating temperatures; this represents a move away from the warmth and controlled environment of Victorian stable complexes. Many believe that modern open-plan stable design (e.g. American barn-type stables) with free air flow and large air volume susceptible to rapid and frequent temperature changes may be responsible for the increased incidence of disease, often viral, mostly affecting the respiratory system, particularly in large commercial yards such as racing stables.

Such modern designs, it seems, were not based on any scientific research or logic with the aim of improving equine health and welfare; rather, they represented a more 'efficient' framework within which to house large numbers of animals and make more efficient use of manpower. Stables need to have good ventilation - with an air inlet (or two) at the front of the box and an air outlet at the back of the box to encourage circulation of air and removal of smells and stale, dust- and spore-contaminated air and its replenishment with fresh clean air. However, stables should offer warm, dry, draught-free conditions. Air inlets and pathways to air outlets should not constitute a draught and ideally the pathway should operate mostly above head height.

Horses kept in cold, damp and draughty conditions are more susceptible to infection and become ill more frequently and are more difficult to treat as well as recovery times being longer. Performance horses cannot tolerate infection if they are to perform to maximum capacity.

The key elements of reducing the risk of cross-infection and illness are adequate air input and exchange, no draughts and as constant a temperature as possible (this does not mean that temperatures have to be high nor stable top doors closed). Horses can be rugged to compensate for low air temperatures but horses do not like draughts. Stables can be warm with good air quality if properly managed.

A stabled horse is thus subject to different management techniques than a horse at grass. Stable hygiene is paramount (removing soiled bedding frequently, keeping drains free, using clean hay or haylage and low dust bedding are all critical factors) in order to reduce the risk of respiratory dysfunction or infection in the stabled horse. Horses which are 'chilled' by draughts have been shown by scientific tests to have their respiratory defence mechanisms adversely affected; if the body's natural defences are compromised in this way not only is infection more likely but also spores and dust are much more likely to cause respiratory disease.

More rugs cannot compensate for lowered resistance; only proper stable design and management can. INDIAN HERBS produce a range of herbal products to assist in the nutritional management of a healthy respiratory system to help maintain open airways and clear lungs. These products can be used to support natural defences in a daily maintenance role in healthy horses or to assist a return to full health where respiratory dysfunction is or has been evident. The products are based on plants traditionally known for their supportive role in achieving and maintaining healthy respiratory function.

If you are concerned about disturbances to normal healthy respiratory function please contact Ann Townsend at INDIAN HERBS EQUINE (TEL/FAX: 01249 760664; MOBILE 0374 640947) at any time for practical advice.

INDIAN HERBS high quality herbal feed supplements bring together the very best of modern veterinary and scientific research and the proven excellence of the 5,000 year old 'art' of Indian Ayurvedic herbal tradition. We sell direct to the horse owner to give the best advice and service whenever and wherever it is needed.

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