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Occasionally performance horses develop a consistent, intermittent or even ‘hacking’ cough following viral respiratory disease. Coughing is a reflex response to irritation or ‘phlegm’ build-up in the airways.
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Causes of chronic coughing
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Certain inflammatory conditions of the windpipe, lungs and throat area, such as Pharyngeal Lymphoid Hyperplasia (PLH), may result in a persistent cough, particularly during exercise. Dusty feeds, stable bedding, tracks and arenas can aggravate the irritation and result in a persistent cough.
In the northern hemisphere where horses are stabled for long periods during the winter months, allergy to dust and mould spores in bedding or feed, and general ‘air’ pollution in poorly ventilated stables can lead to chronic respiratory conditions.
In older horses, these allergies often develop into Chronic Obstructive Pulmonary Disease (COPD). COPD reduces work capacity and causes a hacking, persistent cough. It is also referred to as the ‘heaves’ or ‘broken-wind’.
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Diagnosis of chronic coughing
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The reason for a persistent cough should be investigated by your vet. This usually involves examination of the throat lymph nodes, and internal ‘scoping’ of the throat and windpipe. Horses that are ‘bleeders’ often develop a moist cough soon after hard strenuous exercise or competition.
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Management and therapy
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If the cough is due to a mild throat irritation, a cough relief preparation, such as Kof Kontrol, may be beneficial. It is helpful to dampen all feed, including hay, and minimize dust in bedding by not adding clean shavings or straw as a ‘top up’ for a few days. Place feed and hay in bins or troughs below chest height to help drain the airways.
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Reactive Airway Disease (RAD)
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Low-grade inflammation and irritation of the lining of the trachea (windpipe) and lower airways often persists following viral infection. The condition is known as ‘Reactive Airway Disease’ (RAD) and can persist for months.
Persistent airway inflammation and irritation, and in severe cases, concurrent low-grade bacterial infection, encourages excess mucous (mucopus) to accumulate in the lower airways and lining of the windpipe. The lowering of immunity by stress of training, inhalation of dust from feed, bedding and working surfaces, prolongs recovery, resulting in narrowing of airways, breathing difficulty during exercise and reduced performance.
A history of a ‘moist’ cough or increased respiratory effort and noise when exercising may be associated with a long term RAD problem. The extent of the inflammation and mucopus accumulation can be graded form 0 (clear) to 3 (strands of mucopus hanging form the roof of the windpipe).
Your vet may also collect a sample of mucopus to determine the type of infection and choice of appropriate antibiotics. Therapy with bronchodilators may help clear lower airway debris and a course of oral corticosteroids is often prescribed to treat non-infected, allergic or inflammatory forms of RAD.
Management to assist recovery should include rest in severe cases, dampening all feeds, placing feeders below chest height and using dust free bedding (rice hulls, shredded paper etc.). Normally an improvement is seen in 7 – 10 days, and most horses return to form within 2 – 3 weeks. Consult your vet for advice.
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Pharyngeal Lymphoid Hyperplasia (PLH)
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Inflammation, allergic reaction and ulceration of the lymphoid tissue at the rear of the throat is a common finding in 2 – 3 year old racing and sport horses following a Herpes virus (‘stable virus’) infection in early training. It is though to be due to over reaction of the lymphoid follicle sin the throat triggered by a virus infection, an aggravated by air pollutants and dust in stabled horses in training.
Young horses may develop a chronic cough before and during exercise, particularly when cold air is inhaled during warm-up exercise or under dusty conditions. In mild cases there is often little adverse effect on airway efficiency or performance. In severe cases, the swollen lymph follicles may hang down to obstruct or cause tissue fluid build-up around the larynx, sometimes resulting in a ‘gurgle’ or ‘whistle in the wind’ noise heard during exercise and performance may be affected.
Diagnosis is by ‘scoping’ of the pharyngeal area by your vet to grade the relative severity and size of the reactive area from Stage 1 – 4. Turning a young horse onto green pasture for 4 – 6 weeks will often resolve the problem. In many cases, dampening feed and keeping bedding clean will settle down the tonsil reaction.
In severe cases, antibiotics may be prescribed, combined with light work for 7 – 10 days and reduction in dust. If non-infective nodules are present, a course of oral corticosteroids is often recommended to enable horses to remain in training. In persistent cases, surgical curetting of the excess lymph tissue has been effective. Consult your vet for advice
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Heaves
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The condition referred to as ‘heaves’, Allergic Airway Disease or Chronic Obstructive Pulmonary Disease (COPD) is very uncommon under Australian housing and management conditions. However, 20% of older horses housed during winter in the Northern Hemisphere develop chronic ‘asthma-like’ symptoms of coughing and wheezing characteristic of COPD.
Horses with asthma-like symptoms develop a chronic cough, wheeze on exercise and develop a ‘shallow’ cough when feeding, with a severe reduction in performance. Measures to reduce airborne dust and moulds by selecting good quality hay and low-dust bedding, as well as dampening all feed (or feeding a complete pelleted ration), and providing good ventilation often helps to minimize the long term complications of allergic airway disease. If possible, affected horses should be housed outdoors.
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Article courtesy of Dr John Kohnke from ‘Health Care and problems of Horses, 9th edition’ published by Virbac-Vetsearch.
Dr John Kohnke has over 20 years of experience in the health care and management of horses. He is well known for his ability to give sound, practical and up-to-date advice, which is sought by trainers and horse owners worldwide. As Technical Director of Vetsearch for 20 years, John had an opportunity to pursue research in equine nutrition, parasite control, lameness and respiratory problems.
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