Management of Inflammatory Airway Disease in Pleasure Horses

CHAPTER 61 Management of Inflammatory Airway Disease in Pleasure Horses



Melissa R. Mazan


Airway inflammation caused by exposure to environmental particulates is pervasive in stabled horses and results in varying degrees of cough, poor performance, nasal discharge, poor recovery from exercise, and overheating, among other signs of respiratory compromise. The definition of this syndrome, known as inflammatory airway disease (IAD), has sparked considerable controversy. In this chapter, the term IAD will be used to describe airway inflammation without evidence of bacterial infection, which is what is most commonly recognized in the pleasure horse. In addition to the aforementioned signs, these horses have mild to moderately high counts of neutrophils (greater than 5% and occasionally greater than 50%), mast cells (more than 2%), and rarely eosinophils (more than 0.5%) in bronchoalveolar lavage (BAL) fluid. Although respiratory tract resistance to airflow is often normal at rest, a histamine bronchoprovocation test usually reveals airway hyperreactivity.


Whereas the racehorse with IAD may have subtle signs, such as a tendency to slow down by the half-mile or three-quarter-mile marker or have poor recovery from peak exercise, the pleasure horse often has more noticeable signs of IAD, including nasal discharge and cough that may be paroxysmal at the beginning of work. The pleasure horse with IAD is usually somewhat older than the racehorse—the owner might not detect a problem until the horse is 8 years of age or older—but careful anamnesis often reveals that signs of respiratory disease were present at a much earlier age.


These findings may be explained in light of the athletic effort expended by each of these groups of horses. Racehorses work at a speed corresponding to maximal oxygen consumption (VO2max) from a very early age, and even a small degree of ventilation-perfusion mismatching secondary to increased heterogeneity in the airways can lead to impaired performance long before overt signs such as cough or nasal discharge are seen. The pleasure horse, on the other hand, has a tremendous respiratory reserve that is never tapped. These horses may have gradually deteriorating lung function resulting from inflammation of the small airways (bronchioles) that only over several years manifests as overt signs such as nasal discharge or cough. Pleasure horses with IAD are more likely to have a resting respiratory rate greater than 20, and they often have respiratory sounds attributable to mucoid secretions in the trachea that can frequently be seen on endoscopic examination. Horses that are required to maintain a “tucked in” head carriage, such as dressage horses, Hackney road ponies, and Morgans, may also make an upper respiratory noise when collected.



MANAGEMENT


There are three cornerstones to management of horses with IAD: environmental management, relief of bronchospasm, and long-term reduction of inflammation. Because IAD, unlike heaves, has not been identified with any allergen-mediated component and is most clearly associated with high environmental particulate levels, environmental management ideally leads the charge in treatment of IAD. An extensive and detailed history is critical to initiating environmental change. The field practitioner is in a decidedly better position than a referral clinician in this aspect because a site visit is more useful than even detailed description of the barn and its surroundings.



Barn and Barn Management


Barn dust is rich in particulates from shavings, sawdust, manure, hay, animal hair and dander, and silica from dirt in indoor arenas. Indoor arenas may also be high in biological material, depending on the footing used. Analysis of breathing-zone measurements of respirable dust particles (<4 microns in diameter), which predictably reach the lower airways, reveals that densities can range from 0.003 mg/m3 in an environment in which measures are implemented to maintain “low dust” conditions, to 8.8 mg/m3 in conventional stabling. In comparison, exposure to organic dust containing particulate concentrations as low as 0.1 mg/m3 can result in deterioration of lung function in humans working in swine barns. Moreover, barn dust is also rich in endotoxin, which causes pulmonary neutrophilia in both heaves-affected and control horses and constitutes a strong risk factor for development of IAD in young horses. Important points to note when inspecting a barn include the following:


• Is the barn airy and well ventilated?

• Are the stalls ventilated as well as the aisleways? Many barns are pleasant in the aisleways, but air is oppressively still and without flow inside the stalls.

• Is there substantial dust accumulation on the walls, indicating a high particulate load in the air?

• Is an indoor arena attached to the barn? If so, is a dust suppressant used? How close is the affected horse’s stall to the indoor arena?

• Is hay stored overhead? Is there a tarpaulin under the hay to prevent particulates from raining down on the occupants below?

• Are sawdust or shavings stored and shoveled in the barn?

• Is the barn heated? Many heated barns have reduced ventilation in an attempt to retain more heat.

• Are leaf blowers used to clean the aisles? Are dry aisles vigorously swept? Both activities can create a profound and long-lasting cloud of particulates. Dusty aisles should be sprinkled with water before cleaning.

• Are horses kept in the stalls during cleaning? This is when the most particulates are generated.

• Are horses fed inside? This is another time when high particulate loads are generated.

• What type of bedding is used? Pelleted shavings that are subsequently moistened or paper or cardboard bedding can greatly reduce the level of particulates in the air.

• Is there an automatic insect repellant spray system? This can cause considerable irritation to the airways.

• How are the stalls cleaned? Is there minimum disturbance to the bedding? A commonly employed mucking technique involves throwing the mixed bedding and manure high in the air against the wall of the stall so that the heavy manure falls close to the wall and the lighter bedding falls further away. This may be an effective stall cleaning technique, but a substantial particulate load is generated.


Surrounding Environment


In addition to investigating the barn, it is important to examine the surrounding environment for two reasons. First, particulates generated around the barn affect air quality within the barn. Second, horses may be kept outside the barn for considerable periods. It is useful to determine the following:


• Are the paddocks shaded or sunny? Are trees in the paddocks deciduous or pine trees? Pine trees can result in greater mold growth because there is no respite from the shade as is the case with deciduous trees. Pine trees also generate a considerable pollen load, which carries high concentrations of endotoxin that can result in airway inflammation.

• Do grassy meadows have a high thatch buildup that can result in bursts of mold spores, a further source of high particulate load?

• Are there inorganic sources of particulates in the area, for instance, a gravel road, cement factory, or nearby stone quarry?


Seasonality

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May 28, 2016 | Posted by in EQUINE MEDICINE | Comments Off on Management of Inflammatory Airway Disease in Pleasure Horses

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