Page 74 - December 2020

How well an equine athlete performs is dependent on inborn talent and excellent function of the musculoskeletal system,
with efficiency of all organ systems working together. Limitations on performance, espe- cially in high-speed events, are affected by a horse’s ability to fuel the muscles with oxygen, and this is dependent on the capacity of air that is bellowed through the lungs. An equine ath- lete must be sound in body, and sound in wind. Training and fitness develop strength
and stamina, and emphasis is placed on these strategies in preparing an athlete for the intended task. Yet ironically, it is the 20-plus hours a day that a horse stands idle that are likely to have a significant impact on “soundness of wind,” particularly if stabled indoors. As owner, trainer, or breeder, you have the ability to influence your horse’s environment in ways that promote a horse’s respiratory health, or at the very least not detract from it.
AIRWAY HEALTH
It is helpful to understand what exactly plagues a horse’s airways. Two common lower respiratory syndromes occur in horses: Heaves (also called recurrent airway obstruction or RAO) and inflammatory airway disease or IAD. These are now both
lumped under one heading of Equine Asthma. The latest American College of Veterinary Internal Medicine (ACVIM) consensus statement reports: “Recurrent airway obstruction (heaves) and IAD represent a spectrum of chronic inflammatory disease
of the airways in horses resembling human asthma in many respects.”
Recurrent airway obstruction (RAO) is an inflammatory condition of the lower airways characterized by spasm of the bronchioles, presence of mucous plugs, and chronic changes in the bronchiolar walls – these things combined lead to airway obstruction of the terminal branches of the respiratory tree. The incidence of heaves increases with age, usually occurring in horses older than seven years. RAO is typically caused by allergic responses to inhaled antigens, such as ‘dust’ and mold proteins from feed and bedding.
Clinical signs of a horse with RAO include coughing (productive, wet cough
or unproductive), exercise intolerance, an increased respiratory rate, and flared nostrils. Over time, a double expiratory effort may create a “heave line” caused by hypertrophy (over-development) of the external abdominal oblique muscles of the abdomen.
Inflammatory airway disease (IAD) is associated with reduced exercise tolerance, yet
an affected horse doesn’t typically experience airway obstruction or make excessive efforts
to breathe as with RAO. IAD is a less severe form of airway disease, has no infectious etiology, and tends to occur in young to middle age horses, especially those with exposure to
a stable environment. Notably, these horses
are normal at rest. Telling signs are decreased performance and reduced willingness to perform, as well as having a chronic but intermittent cough. Mucus accumulates within the trachea along with increased numbers
of inflammatory cells identified in tracheal aspirates, bronchoalveolar lavage, or with a lung wash.
The impact of environmental air particulates is significant in the development of equine asthma. Environmental issues, such as inadequate barn ventilation, concentration of respirable particulates and endotoxin, and the quality of bedding and feed, are likely factors in the development of inflammatory airway disease. The dustier the environment, the longer the duration of inflammatory airway disease with convalescence prolonged by environmental contaminants. Lung and throat inflammation occur far more frequently in horses that live the large portion of their day in stalls, especially compared to horses living in pasture.
OPTIMIZING
RESPIRATORY
HEALTH
by Nancy S. Loving, DVM
As owner, trainer, or breeder, you have the ability to influence your horse’s environment in ways that promote a horse’s respiratory health, or at the very least not detract from it.
72 SPEEDHORSE December 2020