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Preliminary observations:
Authors:
S.L. Raymond, B.Sc., E.F. Curtis, B.Sc., A.F. Clarke, BVSc, PhD, MRCVS, Director,
Equine Research Centre
The welfare and well-being of all horses is dependent on healthy lungs. Poor air quality can contribute to various respiratory disorders in the horse. Chronic Obstructive Pulmonary Disease (COPD or Heaves) is the best known disease in this context. This is a full blown allergic response to inhaled mould spores and is seen primarily in older horses.1,2 Air quality can have an impact on the respiratory well-being of young horses in a more covert manner. This condition is known as Lower Respiratory Tract Inflammation (LRTI).3 Poor air quality will also increase susceptibility to, severity and duration of infectious disease, delaying the horse's recovery. The mucociliary clearance mechanism of a horse with a respiratory infection can be impaired for a month after the horse appears to have recovered from an infection.4 During this time the horse's lungs will be particularly sensitive to the effects of dust. Dust in the stable can be an irritant, infectious or allergenic. Each particle can play more than one role. For the purpose of discussing COPD and related disorders, airborne particles can be divided into two groups, "nuisance" dust, including respirable and non-respirable particles and allergens. "Nuisance" dust can irritate the respiratory tract and impair clearance. Allergen sources include pollen, mites, fungi and actinomycetes. The allergen can be in the form of an organism or parts of that organism such as fungal spores or mite excreta. These particles can lead to hypersensitivity in the airways. The chance of a particle inducing disease as a pathogen or an allergen is dependant upon the amount retained in the respiratory tract. This is dependant upon the efficacy of the clearance mechanisms, the pathogenicity of the particle and the susceptibility of the host. Deposition and clearance of particles are dependent on the size, shape and type of particle that is inhaled. It is generally considered that particles are respirable if they are smaller than 5µm. Alternative forage products, including "hayage" have been recommended as a means of decreasing the respirable challenge of dust that horses are exposed to. The goal of this study was to compare the respirable particle levels to which a horse was exposed when fed Horsehae (Tri-Forage Farms Ltd.) and dry hay. Horsehae is mature grass that has been processed damp and bagged in vacuum sealed plastic. In storage it ferments slightly, inhibiting mould growth. This experiment was repeated eight times using one mature standardbred mare. One horse was used as previous studies have shown that horses can behave very differently while feeding.5 The horse was fed according to NRC quidelines and housed in a mechanically ventilated 12' x 12' box stall. The protocol was reviewed and approved by the University of Guelph Animal Care Committee.
The horse was tied for one hour periods while she ate one of the two forage types from a hay net. Sampling continued for one hour or until the horse stopped eating with a minimum sampling time of half an hour. Air samples were taken throughout the sampling time to identify the number and size of particles which were present in the horse's breathing zone while eating. The instrument used was a Rion particle counter
(Hawksley and Sons Ltd) which counts and sizes airborne particles according to five size ranges, 0.3 The two forage types were sampled using a portable airborne particle sampler (Equigiene). The dust from each forage type was assessed microscopically. This was accomplished by placing a sample of feed in a bag and agitating it. The portable sampler, which holds a microscope slide with mountant gel7, was turned towards the bag for three seconds. The microscope slides were examined under an Olympus, BX50 microscope (Carsen Group Inc.) and the types of particles were identified and categorized as follows:7 I Negligible quantities of mould spores present, the principal dust constituents being plant hairs, pollen grains and other plant and miscellaneous fragments. II Mould spores present, primarily of the large-spored, 'fairweather air spora' types, eg, Alternaria sp., Cladosporium sp.. Small numbers of respirable spores such as Penicillium sp. and Aspergillus sp., in the 2 to 5 µm size range may be present. A lot of plant material present.
III Primarily large numbers of respirable spores. Occasionally the major constituents are actinomycete spores of approximately 1 µm diameter. Samples with evidence of heavy dust mite infestation are also included in this category. Particle assessment:
Counts in four particle size ranges, 0.5
Table 1. Mean number of particles per .1L of air.
Microscopic assessment: The types of particles observed from the forages are listed in Table 2.
Table 2. Particle identification from samples.
Figure 1. Dust Particles Detected Within the Breathing Zone of the Horse
The main source of respirable dust in stables is feed and bedding. The key to the prevention and control of respiratory disorders is to minimize the animals' exposure to airborne challenges. Two ways to reduce the challenges are to decrease contaminants from the source and to increase clearance of these contaminants. Studies have shown that symptomatic COPD horses can become asymptomatic with proper environmental control.1,2,9,10,11 One study has shown that symptomatic COPD horses when housed on shredded paper and fed a cubed diet became asymptomatic in 4 to 24 days.9 Pulmonary function values from these asymptomatic horses did not differ from the control group. When examining the dust produced under different management conditions the conventional method (hay and straw) has been shown to have higher total and respirable dust challenges and contain higher levels of aeroallergens than controlled conditions (wood and pelleted diet).12 Two specific agents have been shown to contribute to COPD. These are Aspergillus fumigatus (a thermotolerant fungus) and Faenia rectivirgula (formally Micropolyspora faeni, a thermophilic actinomycete).13 However, a wider variety of agents and conditions could contribute to this condition. Along with the respiratory challenges which contaminated hay presents there may be nutritional concerns. Mouldy feeds contain mycotoxins which could induce digestive problems in the horse.14,15 The nutritional status of the hay could be altered.14,15 The most important factor which dictates the quality of the hay is the moisture content during baling. The higher the moisture content the higher the contamination with aerobic, thermophilic or thermotolerant organisms. The product Horsehae is baled with a high moisture content but is sealed in air tight bags thus, preventing aerobic microbial growth. The threshold limiting value (TLV) of dust to which the healthy horse can be exposed is unknown and probably varies with individuals.10 The accepted TLV of organic dust to which human workers can be exposed for an eight hour day is 10mg/m3 16, although research has shown that 5mg/m3 can contribute to respiratory problems in grain handlers.17 A horse with an allergy develops a hypersensitivity to the allergens found in its environment reducing its TLV. In this study, the respirable challenge to the horse while feeding was shown to be significantly lower when Horsehae was fed as compared to dry hay. Microscopically, the forage, Horsehae, showed fungal contamination typical of a grade I sample as categorized by Clarke, 1987. The primary constituents being, plant material and some spores of common airborne "field" fungi. These "field" fungi spores are commonly found on plants as they grow in the field and are present as the plant is processed. The hay fed in this study showed fungal contamination typically found in grade II samples as categorized by Clarke, 1987. Proper attention to air quality will not only help alleviate the symptoms of COPD and help shorten the duration of respiratory infections but if practised initially will decrease the incidence of respiratory disorders. Keeping the levels of dust and ammonia to which horses are exposed as low as possible plays a large part in creating and maintaining an environment of high air quality. The use of this forage, Horsehae, shows potential in the successful management of such an environment.
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particles<0.5µm, 0.5
5µm
