Five of the most common respiratory tract problems

Equine influenza

A highly infectious virus, equine influenza is spread by inhalation from a distance of up to 30m. It infects the cells lining the upper and lower respiratory tract causing inflammation of the larynx, trachea, bronchi and bronchioles and a loss of the specialised ciliated epithelium lining these airways. This can then make infected animals susceptible to secondary bacterial infection of the airways. Equine influenza should be routinely vaccinated against. This will also stop it spreading between horses.

Summer pasture associated obstructive pulmonary disease

Similar in presentation and aetiology to equine asthma (see below), SPAOPD is caused by allergens encountered by the horse when he’s turned out in his paddock.

Equine asthma

Also known as recurrent airway obstruction or chronic obstructive pulmonary disorder, equine asthma is a common allergic inflammatory response triggered by stable dust, spores and allergens causing periods of reversible airway obstruction. It’s the smaller airways — the bronchi and bronchioles — that constrict, become inflamed and produce excessive mucus. This then causes the horse to cough, have difficulties breathing and show signs of poor performance. Often, once a horse has had an asthma attack, the airways become hypersensitive and respond in a similar way to non-specific allergens in the future. Diagnosis may require endoscopy to view the inflammation in the lungs and collect samples of the fluid, mucus and cells that are also present.

Recurrent laryngeal neuropathy

Also known as roaring, this occurs when there is damage to the recurrent laryngeal nerve, usually the left one due to its longer course in the body. The recurrent laryngeal nerve supplies nerves to the cricoarytenoideus dorsalis muscle that retracts the cartilage in the larynx. When not retracted, this cartilage obstructs the airway, creating turbulent air flow, which causes the roaring noise heard when affected horses inhale. It also reduces the volume of fresh air taken into the lungs. Laryngeal paralysis is graded by endoscopy at rest and at exercise, as sometimes the paralysis is reversed when the horse has been moving. Treatment is not required in all cases, but some will need surgery to tie back the paralysed cartilage.

Exercise-induced pulmonary haemorrhage

A disorder most commonly seen in racehorses due to strenuous exercise over short periods of time, EIPH is when blood occurs in the lungs due to an increase in pressure in pulmonary blood vessels. The vessels become weakened and, as the pressure exceeds the limit they can withstand, they rupture. Between 50 and 75% of racehorses have evidence of EIPH up to two hours after racing, but only 1-4% have such significant bleeding that it’s seen coming from the nose, known as epistaxis. Signs of EIPH include poor performance or stopping during exercise. Other times, it goes unnoticed, with no clinical signs.

Even horses turned out in summer can have respiratory issues

N O S N I K C I D A J N A H : O T O H P Mucus build-up is a c ause o f a sthma

Y R A R B I L R E U A B : O T O H P Vaccinate your horse against equine flu

N O S N I K C I D A J N A H : O T O H P ▼ Roaring i s caused b y damage to the re current laryngeal nerve

Y R A R B I L R E U A B : O T O H P ▼ Racehorses a re p rone t o bleeding in the lungs