Respiratory System and Problems

• Epiglottis


  • Rests above soft palate when not swallowing, forming airtight seal
• Equine respiratory system


  • Responsible for O2 / CO2 exchange
  • Enables athletic ability
• Increasing breathing rate and depth

  Achieves tidal volume of 4 - 75 litres air per second
• Breathing is synchronised to stride in gallop, limiting respiratory system
• Unlike heart and skeletal muscle, the respiratory system cannot be 'trained' to be 'fitter' - can just ensure it's as healthy as possible
• Respiratory dysfunction / disease


  Reduced potential performance
• Signs of respiratory disease

  • Increased breathing rate, depth, effort
  • Change in breathing pattern
  • Fever
  • Coughing
  • Off food / depressed
  • Flared nostrils
  • Nasal / eye discharge
  • PPS (Poor Performance Syndrome)
• Causes of respiratory problems

  • Infectious diseases (viruses, bacteria, fungi, parasites)
  • Non-infectious (allergies, over-exertion, foreign bodies / obstructions, genetic defects, sinusitis, blood clots, guttural pouch infections, neoplasia)
• Equine Influenza

  Affects upper and lower respiratory tract
• Equine Influenza is spread by direct contact, fomites and aerosol, and is VERY contagious
• Equine Influenza viral subtypes


  A/Equi1 and A/Equi2
• Equine Influenza symptoms include coughing, depression, fever, PPS, loss of appetite, nasal discharge, and secondary bacterial infections
• Recovery from Equine Influenza takes at least 3 weeks
• Horses shed the Equine Influenza virus for 3-10 days post-infection, including immunised horses, but there is no carrier status post-infection
• Horses most at risk from catching Equine Influenza

  • Any which are moved or come in contact with horses which have moved (competition, import, sale, etc.)
• Treatment for Equine Influenza


  1. Good nursing with isolation to avoid spread

  2. Antibiotics for secondary infections
• EHV1

  • Upper respiratory tract infection - depressed immune system, fever, PPS, soft cough, nasal discharge, dull, depressed, lose appetite, diarrhoea?
  • Causes abortions, stillbirths, foal weakness / death
  • Causes neurological disease
• EHV1 - Paralytic form

  Posterior ataxia, recumbency
• Horses can shed EHV1 virus for up to 14 days post-infection, and have latent infections that can be shed when stressed
• EHV4

  Just respiratory disease
• Treatment for EHV1 and EHV4


  1. Complete rest for 3 weeks, good nursing

  2. Antibiotics for secondary infections

  3. Sling if paralytic but prognosis very poor
• Control of EHV 1 and EHV4 to prevent abortion

  1. Divide pregnant mares into small groups and isolate

  2. Isolate all new animals for 14-21 days

  3. Do not mix mares carrying first foal with older mares

  4. If remove mare from group do not put back in same group

  5. Vaccinate

  6. Pregnant mares to have no contact with weanlings / other horses

  7. Foster mares no contact with pregnant mares
• There are effective vaccines available against Equine Influenza and EHV
• Flu vaccination is required for all horses under BHA and FEI rules, plus riding club, pony club, etc.
• EHV vaccine is used in breeding stock and should be used more widely
• Rhinovirus & Adenovirus

  Cause mild, 'cold'-like infections that may impair performance
• How to test for a viral infection

  • Antigen testing (nasopharyngeal swab for PCR or culture)
  • Antibody testing (blood sample for serology, ELISA)
• Equine Viral Arteritis (EVA)


  • Notifiable disease affecting stallions and breeding mares
  • Causes respiratory disease and abortion
  • Stallions can be carriers
• Equine Viral Arteritis is transmitted via direct/close contact, sexual transmission, and fomites
• Horses most at risk from Equine Viral Arteritis


  • Breeding stock
  • Imported horses
  • Close contacts of both of these
• Exotic notifiable viruses

  • African Horse Sickness (respiratory and cardiac forms, often fatal, transmitted by biting midges)
  • West Nile Virus (neurological disease, transmitted by mosquitos, reservoir in birds, zoonotic)
  • Equine Infectious Anaemia (Swamp Fever - chronic, recurring fever, transmitted by horse flies)
• Strangles

  • Caused by Streptococcus equi, VERY contagious
  • Incubation period 7–10 days (3-21 possible)
  • Survives in environment for up to 9 weeks
  • Shedding can be variable and last for months or occasionally years after disease signs have disappeared
• Strangles clinical signs

  • High temperature
  • Lethargy/dull and depressed
  • Reluctance to eat/drink, difficulty swallowing and/or a lowered head and neck
  • Cough (although not always present or as common)
  • Thick and discoloured nasal discharge
  • Swelling of the lymph nodes (glands) under the jaw, in the space between the head and neck, or on the head or neck which may lead to the formation of abscesses
• Systemic Strangles ("Bastard Strangles")

  Pneumonia / Guttural Pouch disease due to inhaled pus
• Treatment for Strangles


  1. Good nursing, + antibiotics, NSAIDs

  2. 95% survival rate
• Pneumonia


  • Can be viral or bacterial
  • Bacterial causes include Streptococcus, Rhodococcus, E.coli, Pasteurella
  • Symptoms include depression, cough, difficulty/ painful breathing
• Pneumonia diagnosis


  • Nasopharyngeal swab
  • Tracheal wash
  • Serology
• Nasal Aspergillosis

  • Non-invasive and invasive / destructive forms
  • Persistent foul-smelling nasal discharge, usually unilateral
  • Invasive form can cause severe bleeding out / death
• Treatment for Nasal Aspergillosis

  Anti-fungal medication
• Equine Parasitic Respiratory Diseases

  • Parasitic pneumonia (Parascaris equorum in foals)
  • Lungworm (Dictyocaulus arnfieldi in donkeys and in-contact horses)
  • Pulmonary hydatidosis (Echinococcus granulosis var equinum - tapeworm cysts in lung)