SAEVA Congress 2018 Proceedings | 12-15 February 2018 | ATKV Goudini Spa
The environment in which racehorses are housed and the management procedures to which they are exposed is frequently at odds with the requirement for optimal lung function during maximal performance . Inhalation of a variety of different noninfectious agents has been proposed to cause IAD and many of these agents are found in the stable and training environment . When horses are housed in stables , they are likely to be exposed continuously to high concentrations of dust . The airborne dust in equine stables contains a range of organic and inorganic compounds which include bacteria , viruses , moulds , mite debris and their faeces , plant material , bacterial endotoxins , β-glucans and inorganic dusts . Furthermore , the dust found in stables has a variable composition depending on the source and conditions under which the bedding and feed materials were grown , harvested , and stored . These airborne compounds are potentially able to induce airway inflammation either by initiating infection , by inducing allergy , by direct toxicity , or indirectly by overwhelming pulmonary defence mechanisms . The association between chronic respiratory tract disease in older horses ( RAO ) and dusty and mouldy hay or bedding is well established , and inhalation of respirable dusts is also thought to induce IAD in other horses , particularly younger ones . The principal difference between RAO and IAD is that RAO is associated with increased respiratory effort at rest , while IAD is not .
Exercise alone can result in non-specific airway inflammation . One study found horses undergoing 10 weeks of training had more airway inflammation than nonexercised stable mates . The cause of this inflammation was not documented , but exercise may cause increased deposition of irritant particles in the distal airways associated with the 20-fold or greater increase in minute ventilation that occurs during strenuous exercise . Strenuous exercise also impairs pulmonary macrophage function , alters peripheral lymphocyte function , and increases the concentration of cortisol in serum for up to 24 hours all of which may help predispose to inflammation .
Alternatively , exposure of the lower airways to unconditioned air , as may occur in cold climates , may cause airway inflammation as has been demonstrated in humans and laboratory animals . It has been suggested that even in relatively moderate conditions ( 4 ° C and exercise at only 6-8 m / sec ) unconditioned air may penetrate into the periphery of the equine lung during exercise . Inhalation of unconditioned air can cause reflex bronchoconstriction and mucosal sloughing in horses , with the latter inducing airway inflammation . Therefore , hyperventilation , particularly with very cold air , may be a potential cause of inflammation of the lower airways .
Clinical Signs
Regardless of the definition , or whether it causes overt signs of respiratory disease , airway inflammation is common in performance horses , particularly young ones . Studies on the prevalence of airway inflammation in young performance horses have defined IAD as either the presence of increased amounts of mucopus within the trachea ( as observed via endoscopy ), or the presence of increased neutrophils within tracheal washes or bronchoalveolar lavages ( BAL ; as identified by cytological evaluation ). On the basis of these definitions airway inflammation occurs in 11.3 -
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