Skip Ribbon Commands Skip to main content
Share This

Disease Information

Diseases and Health Problems of Horses

Equine Gastric Ulcer Syndrome
Equine Gastric Ulcer Syndrome (EGUS) is increasingly recognized as a major problem affecting the well being and performance of horses. In fact, stomach ulcers are quite common in horses.

  • Up to 93% of racehorses get stomach ulcers, regardless of age
  • Almost 60% of other performance horses have ulcers
  • Up to 57% of foals have stomach ulcers, particularly during the first several months of life

Equine ulcers can be difficult to diagnose

  • 50% of horses with ulcers show no outward signs of gastrointestinal disease

Views inside a healthy horse stomach (left) and a horse in training with ulcers (right). Photos courtesy of MJ Murray.

Signs of equine Gastric Ulcer Syndrome (EGUS) range from mild to severe – cases of perforated equine gastric ulcers can even be fatal.

Parasites of Horses
All horses should be included in a regular parasite control program. Foals should be treated initially at 6 to 8 weeks of age, and routine treatment repeated as appropriate.

Click below for information about equine parasites (PDF format):

Viral Diseases of Horses

Eastern and western encephalitis (encephalomyelitis)
These variations of equine encephalomyelitis are clinically similar syndromes characterized by signs of CNS dysfunction and moderate to high mortality. The causal arboviruses are transmitted by mosquitoes or ticks and infect a variety of vertebrate hosts, including man, in which they occasionally cause serious infections. Horses may be infected by alphaviruses including eastern (EEE), western (WEE), and Venezuelan (VEE) equine encephalomyelitis viruses. Clinical signs of an encephalomyelitis occur approximately 5 days after infection, and most deaths occur 2-3 days later. Signs can include fever, impaired vision, irregular gait, wandering, reduced reflexes, circling, incoordination, yawning, grinding of teeth, drowsiness, pendulous lower lip, inability to swallow, photophobia, head-pressing, inability to rise, paralysis, occasional convulsions, and death. Mildly affected animals may recover slowly in a few weeks but may have residual brain damage. Mortality in horses is 20-50% from WEE, 50-90% from EEE, and 50-70% from VEE.

Equine influenza is an acute, highly contagious, febrile respiratory disease. The clinical outcome following viral exposure largely depends on immunological conditioning; in susceptible animals this may vary from a mild, inapparent infection to a severe disease that is rarely fatal except in young, old, or debilitated horses. Transmission occurs via the respiratory route through contact with infective respiratory secretions. Epidemics arise when one or more acutely infected horses are introduced into a susceptible group for show, sale, training, or racing.

Horses are the most sensitive species to this disease, with the possible exception of humans. Tetanus is a toxemia caused by a specific neurotoxin produced by Clostridium tetani in necrotic tissue. The incubation period varies from one to several weeks, but usually averages 10-14 days. Localized stiffness, often involving the masseter muscles and muscles of the neck, the hindlimbs, and the region of the infected wound is seen first; general stiffness becomes pronounced approximately 1 day later, and tonic spasms and hyperesthesia become evident. Mortality averages 80%.

Rabies is an acute, viral encephalomyelitis that affects all warm-blooded animals. The mortality rate approaches 100%. The incubation period is prolonged and variable. Rabid animals of all species exhibit typical signs of CNS disturbance. Horses may show extreme agitation evidenced by rolling, as with colic. They may bite or strike viciously and, because of size and strength, become unmanageable in a few hours. Such animals frequently suffer self-inflicted wounds.