equine asthma

• Pasture associated asthma also occurs, usually with a seasonal pattern (summer) in horses at grass.
• There is a possibility of a continuum from mild asthma (poor performance) to moderate asthma (cough, mucous nasal discharge, tachypnoea during exercise) to finally severe asthma (signs at rest). Most cases are treated do not recur but some may progress into more severe asthma, this is dependent on the endotype. Hence, it may be better described as a spectrum rather than a continuum. Inflammation is central to the syndrome but the mechanisms are poorly understood. There is a strong association with environment and feeding.
• fill in the blanks

  A) young

  B) 7

  C) no

  D) with

  E) occasional

  F) frequent

  G) stabled

  H) neutrophils

  I) eosinophils

  J) macrophages

  K) neutrophils

  
• The breathing zone is around 30cm around the horses nose and hence respirable dust in this area is the most critical. Particles larger than 5um can trigger disease (these can go deeper into the lung), these particles can be…

  • Molds and fungi
  • Pollen
  • Endotoxins
  • Chemicals: ammonia, smoke, exhaust fumes..

  Airborne respirable dust (ARD) is in low concentrations in steamed hay and higher from nets

  • 4x higher [dust]
• Causes of equine asthma include…

  • Non-allergic inflammatory responses
  • These can be triggered by one or all of the following: Endotoxin, moulds and noxious gases
  • Genetic or familial
  • There is a familial risk for moderate/severe CS
  • RAO -criterion of heritability soundness in breeding stallions?
  • Hypersensitivity reaction
  • Exacerbation with hay dust
  • Allergic reaction? hypersensitivity type I & III
  • Possible role:
  • Faenia rectivirgula
  • Aspergillus fumigatus
  • Thermo-active nomyces vulgaris
• The following have a central role in the pathophysiology of equine asthma…

  • Airway hyperresponsiveness
  • The smooth muscle overreacts constricting airways in response to a trigger. Overtime these muscles can hypertrophy.
  • Bronchospasm
  • Airway obstruction secondary to inflammation
  • Inflammation
  • Airway neutrophilia is characteristic and activation of macrophages can occur
  • Mucus accumulation
  • This is a consistent finding in equine asthma (especially RAO)
  • Tissue remodelling
  • Increased smooth muscle mass
  • Increased contraction force
  • Peri-bronchial fibrosis
  • Epithelial hyperplasia
• Diagnosis of equine asthma include…

  • History
  • PE
  • Auscultation
  • Rebreathing bag! (look for tolerance, cough, recovery!)
  • The higher CO2 causes stress which allows for better auscultation to hear pathology such as wheezes, crackles, and tracheal rattles. Care not to over stress the horse so do not perform in the dyspnoeic horse
  • Especially important for mEA
  • Endoscopy
  • To rule out upper airway diseases
  • Cytology (BAL & TTW)
  • Pulmonary function testing
• Ideally, perform endoscopy 1 hr post-exercise to better assess tracheal mucus. Carina (the bifurcation) should be reached and allow for an assessment of the main bronchi
• a transtracheal wash / aspirate provides a sample representing both lungs and is a good screening test as well as being the preferred method for culture and sensitivity.

  • Diagnostic accuracy for mEA is unknown
• bronchoalveolar lavage provides a sample of one lung (specifically a terminal bronchi) so is more specific and is better for diffuse pathology. Hence it is the preferred method for equine asthma diagnosis
• • On cytology, macrophages are the most abundant cells, followed by lymphocytes. Neutrophilia is the most common abnormality in LRT samples.
  • The % is higher in TTW (5 to 80% in normal horses!)
  • Should be less than 5% in BAL fluid
  • Mast cells are uncommon (special stains)
  • Eosinophils should be less than 2% in BAL fluid
• there are two cytological profiles of BAL

  A) 3

  B) 10

  C) 5

  D) 5

  E) 25

  F) degenerated

  
• Horses with mEA, Sea and SPAOPD are treated with…

  • Glucocorticoids (a type of corticosteroid)
  • Bronchodilators
• Horses with mEA are also treated with (glucocorticoids and bronchodilators) but also…

  • Immune modulation (Interferon-alpha)
  • Decreased relapse rate has been shown in some studies but the practical experience mixed
  • Omega-3 supplementation
  • (1.5-3g DHA) mEA& sEA
  • Cromoglicate: mast-cell mediated mEA (IAD)
• Glucocorticoids (a type of corticosteroid) have a high efficacy so there is an extensive use. They impact on…

  • Lung function
  • Airway inflammation
  • Bronchial remodelling
  • However, there are adverse effects such as..
  • Adrenal suppression (fluticasone, Ciclesonide)
  • Adrenal gland atrophy (due to the reduction on endogenous cortisol)
  • Immune suppression
  • Laminitis
• For acute severe equine asthma use the following treatment protocol…

  • IV dexamethasone: 0.04-0.1 mg/kg SID followed by PO Dexa0.05 mg/kg or prednisolone 1 mg/kg SID until respiratory effort & nasal discharge resolve
  • Then follow with Inhaled GC
  • Beclomethasone dipropionate 3750 ug BID
  • Fluticasone 2000 ug BID (preferred)
• For mild equine asthma use the following treatment protocol…

  • Start PO Dexamethasone 0.05 mg/kg or prednisolone 1 mg/kg SID (4 weeks). Followed by inhaled glucocorticoids
  • Beclomethasone dipropionate 500-1500 ug BID
  • Fluticasone 2000 ug BID initially
  • Tapered over 4 weeks
• • Bronchodilators are used along with glucocorticoids (not stand-alone therapy)
  • Beta-adrenergic (clenbuterol, albuterol, salbutamol)
  • Systemic sEA& SPAOPD (mEA inhaled)
  • Salmeterol
  • Albuterol
  • Ipratropium bromide
  • Clenbuterol
  • Parasympatholytics (ipratropium)
  • Systemic beta-adrenergic bronchodilators can have adverse events such as…
  • Cardiovascular remodelling
  • Tachyphylaxis
• Ciclesonide is a pro-drug that does not affect cortisol levels. It is an inhaled glucocorticoid which is licensed however is very expensive and difficult to use
• Management for equine asthma involves environmental and feeding changes

  • Keeping the horse outside at all times
  • Ensure access to a well-ventilated shelter that is free of urine/manure (ammonia fumes)
  • Feed pelleted feed or hay cubes (to reduce respirable dust)
  • Provide soaked hay / steamed hay, haylage (hay that has a higher percentage of moisture and hence a lower portion of respirable dust)
  • When stabling, ensure low respirable dust which can be done with the use of…
  • Cardboard and dust-free shavings
  • Steamed hay, haylage
  • Pelleted rations
  • Similar alterations in surrounding stalls
• • Respirable dust 30cm around the nose (the breathing zone) is most critical so…
  • Do not feed in nets
  • Do not feed round bales outside
  • Provide feed at ground level
• Clinical remission (normal pulmonary function) of severe equine asthma occurs in 4 to 8 weeks. While the reduction in smooth muscle mass takes 12 months

  • Horses remain more susceptible compared to healthy horses
• further advice includes...

  • Sprinkle the aisles with water before sweeping
  • Avoid overhead hay storage (use tarp)
  • Turn bedding banks every day (corners included!)
  • Remove horses from stalls while cleaning (30m)
  • No blowers indoors
  • Make sure stalls have good ventilation
  • At least 1 inflow & 1 outflow
  • Keep barn doors open (this can reduce respirable dust for up to 30%)
  • Identify areas of inadequate ventilation, these can be identified via
  • Commercially available devices(expensive)
  • Cobwebs
  • Condensation ceiling
  • Layer of dust