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Respiratory Health: How Winter Affects Your Horse

galloping

Introduction

Good respiratory health is particularly important for performance horses who gallop, e.g. racehorses and eventers, since they rely on clear, healthy airways to deliver large amounts of oxygen during exercise. After lameness, respiratory problems are the most common cause of poor performance. Some physiologists have stated that the respiratory system may be the ultimate limiting factor to high intensity exercise in the horse.

The 2015-16 winter of mild, wet weather has meant that many UK horses and ponies have been stabled even more than usual. The amount of turnout and how quickly the land gets poached has caused many yard managers and owners to limit turnout or in some cases, give none at all.

Such long periods being stabled poses a big challenge to the horse, for his digestive, mental, physical and respiratory health. Research studies have shown that even the cleanest stables challenge horses’ respiratory health, causing inflammation. This applies to all horses, whether or not they have allergies such as recurrent airway obstruction (RAO, used to be called COPD).

The equine respiratory tract

The horse’s respiratory tract, like many other of its body systems, reflects its superiority as an athlete. From the wide, flaring nares of the nostrils, to the remarkable ability to transfer oxygen from the lungs to the body tissues the horse’s respiratory and cardiovascular systems make it an expert in transforming breathed air into muscle stamina.

A galloping horse might take over 150 breaths a minute, with each breath taking less than half a second! At full gallop, a horse may breathe up to 1800 litres of oxygen per minute, equating to about 50 litres per second. Horses can take up about 40 times the amount of oxygen at maximal rates of exercise compared to rest, while a human athlete can take up about 7 times the amount.

Air is breathed in through the nostrils (horses cannot breath through their mouths) and then warmed and filtered in the nasal passages. It passes through the nasopharynx and larynx – the throat and voice box, down into the trachea. The upper respiratory tract consists of all the structures up to the larynx, after which the structures are called the lower respiratory tract. The trachea branches into two bronchi within the chest, each of which leads to a lung. The bronchi divide and then subdivide into bronchioles within the lungs, which lead to tiny air sacs called alveoli, where oxygen is transferred into the blood, to be carried to the body tissues including the working muscles.

The flaring of the nostrils is an important factor in reducing resistance to airflow, thus allowing maximal rates of oxygen uptake in the galloping horse. Restriction from nosebands could have a detrimental effect, and nasal strips which flare the nostrils may help, so these should be considered for the performance horse.

Respiratory challenges

Stabling challenges the horse’s respiratory system by exposing the horse to large amounts of respiratory pathogens, including airborne particles mostly from bedding and forage. These pathogens include mould spores, tiny plant particles, dust mites and their droppings, endotoxins and noxious gases like ammonia.

These pathogens can irritate and/or inflame the lower airways. Irritation or inflammation causes a narrowing and spasm of the lower airways and production of thick mucus, both of which restrict oxygen delivery. Some mucus is normal – it helps to pick up irritating particles, which are then cleared from the lungs by tiny hairs called cilia, which beat upwards, and coughing. But when challenged, the lungs produce greater quantities and much thicker mucus than normal, which are a problem.

Allergic airway disease is a common cause of respiratory problems, especially in the stabled horse. The term chronic obstructive pulmonary disease (COPD) has been superseded by recurrent airway obstruction (RAO), because advances in understanding of the condition revealed its similarity to human asthma. Removal of the offending inhaled allergens from the environment is the first most important factor in treatment. Medical treatments have advanced significantly in the past decade, with availability of inhaled corticosteroids to dampen the inflammatory response, inhaled or systemic drugs to dilate the airways (bronchodilators) and drugs that loosen and clear mucus (mucolytics).

Mild lower respiratory tract disease may not show up in resting horses or leisure horses who are in very light work. If your horse coughs at all, even if it is just a couple of times as you pick up trot, take action. Horses have a lower cough reflex than humans, so substantial inflammation or irritation will be present before the horse starts to cough. Coughing is used as the most reliable indicator of lower airway disease, and listening to breathing alone is unreliable. Endoscopy, which allows the airways to be looked at, is useful for diagnosis. Nasal discharge may or may not be present, because the horse may swallow all the excess mucus produced.

Management

Prevention is most definitely better than cure. The key factor in maintaining respiratory health is to avoid inhalation of irritants and allergens in the first place. Turn the horse out as much as possible. Some horses with stable-associated RAO will only remain healthy living out. If stabling is unavoidable, ensure good ventilation, keep the horse’s environment as clean as possible, and pay close attention to stable bedding and forage, the two main offenders in respiratory disease in stabled horses.

Choose dust extracted bedding, and be aware that vets tend to recommend paper or cardboard as the safest bedding for good respiratory health. Never deep litter because it causes noxious gases and a huge load of mould spores, both of which are harmful to the airways. Muck out thoroughly daily. Keep the muck heap away from stables and avoid hay lofts over stable ceilings.

Haylage is a better choice for respiratory health than hay due to its lack of dust and mould spores, and most UK-made hay is too high in both to be suitable for feeding dry inside stables. Hay is the single most common source of fungal spores for horses and dusty samples have been measured to have over 64,500 fungal particles per milligram compared to around 2 in branded haylage. Either soak or steam hay before feeding to stabled horses. Soaking hay for at least 10 to 15 minutes dampens dust and swells mould spores (meaning they are swallowed rather than inhaled), but any longer and nutrients will be leached out. Never feed obviously mouldy or very dusty hay to horses, even after soaking (or steaming) because ingestion of high levels of mould spores can cause other health problems.

Steaming hay might be a better alternative because as well as dampening tiny, irritating particles and swelling mould spores, it kills bacteria and any active moulds. Research has shown that up to at least 98% of bacteria in forage are killed by steaming for a minimum of 10 minutes in a sealed, insulated chamber.

Clean and dust-down the stable regularly, with the horse removed. This might seem excessive, but it will significantly reduce exposure to irritants and allergens. Be aware of adjacent stables because air hygiene of the surrounding area is just as important as that of the horse’s actual stable.

Effective medical treatments for RAO are available but they must be adhered to, usually over extended periods, if they are to be effective. Most horses will have to be trained to accept an inhaler because it can elicit a fearful response. Bacterial infections are actually quite rare in horses with RAO, so antibiotics are mostly useless. If RAO affected horses are not treated effectively, long term effects include damage that can take a long time to respond to therapy, or even irreversible damage.

Environmental management is even more important than medical treatment because it can remove the cause of airway disease, helping the horse to have a healthier respiratory tract. Drug treatments will not compensate for poor air hygiene.

Feeding

The most important nutrition factor for airway health in stabled horses is the forage, which must be dust and mould-spore free. No amount of medical treatment or supplementation can make up for dusty hay. Horses affected with RAO cannot cope with even the cleanest hay so it must be soaked or steamed, or haylage fed instead.

Feed hygiene is important to ensure good respiratory health, especially in stabled horses. Feeds should be dampened to avoid any dust being inhaled and feed buckets and utensils used for mixing should be cleaned daily to avoid mould build up.

Protein should not be overfed because the excess urea produced from excess protein intake is converted to harmful ammonia by bacteria in stable bedding. Excessive protein will therefore cause an increased exposure to noxious gases for stabled horses.

As for all horses, a balanced diet is important to avoid deficiencies that could be detrimental to respiratory function. A deficiency of zinc, for example, will inhibit immune function and make the horse more susceptible to respiratory infections. Zinc is also a key antioxidant nutrient, which is particularly important in cases of tissue irritation, damage or inflammation. Horses with respiratory challenges will benefit from extra zinc over and above normal recommendations.

Hard working horse Respiratory challenge
Daily requirement of zinc (mg) for a 500 kg horse 600-700 750-850

Chronic airway inflammation, such as that involved in RAO, results in oxidative stress, and researchers have shown that vitamin C in lung fluid is depleted in horses with airway inflammation including RAO. Vitamin E is another antioxidant that interrupts damaging oxidative chain reactions, and has been shown to improve lung function. Horses with respiratory challenges should be fed elevated levels of vitamins C and E, and plant antioxidants.

Grapeseed extract is a powerful antioxidant, due to its high concentration of polyphenols, including proanthocyanidins. Proanthocyanidins inhibit the release of inflammatory mediators and are believed to have antibacterial and antiviral activity. Bioflavonoids from citrus extract including hesperidin and naringin are included for even more antioxidant activity. Citrus flavonoids have powerful antioxidant and anti-inflammatory properties.

For horses with airway challenges, certain herbs can be very useful to soothe inflammation and airway spasm, and help get rid of excess mucus. Herbs including garlic, elderflower, thyme, rosemary and plantain are useful for respiratory support. Garlic (Allium sativum) is a well-known antimicrobial, expectorant and antispasmodic which has been used throughout history for its beneficial effects on the respiratory system.

Rosemary (Rosmarinus officinalis) is antimicrobial and anti-spasmolytic, useful to help soothe airways. Thyme (Thymus vulgaris) is an antiseptic and expectorant, helping to ward off bacterial attack. Plantain (Plantago major) is a bronchodilator, easing the constriction associated with allergic airway disease.

ReadySupp Lung Aid is a powerful combination supplement that is formulated to help soothe airways, encourage clearance and maximise airflow for optimum respiratory performance. It contains a blend of all the ingredients explained above.

Read more about ReadySupp Lung Aid at www.readysupp.com

Lung Aid


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