URTICARIA or Hives
Urticaria (hives) is one of the most common skin problems faced by horses. It is the result of a hypersensitivity (allergic) reaction and identified as multiple raised, oedematous(fluidy), flat topped swellings, which often will dent or ‘pit’ when pressure is applied to them. Although occasionally itchy they usually cause no discomfort to the horse. Any age or type of horse can be affected, though thoroughbreds are probably over-represented.
CAUSES
Many things can cause a horse to have an urticarial reaction, including food, medication, insect bites, stings, pollens, mould or fungal spores, extreme temperatures, stress and many others. Reaction to direct skin contact is less common. It is often impossible to identify what has caused the reatcion, particularly as there may be a delay of several hours between exposure to the agent and the resultant reaction.
Although further investigation such as skin biopsy can confirm an urticarial reaction it will rarely identify the cause.
TREATMENT
The majority of sudden onset cases of urticaria will spontaneously resolve in 24-48 hours, so if the horse is not otherwise affected it may be best to hold off any treatment, initially. However, if the horse shows any signs of discomfort or distress then treatment should be sought immediately.
The most common and usually the most effective treatment is an intravenous injection of corticosteroid, which blocks the production of inflammatory substances which are what cause the wheals to form. Steroids need to be used with care, particularly in horses at risk of other conditions, such as laminitis and in competition horses, where it is a restricted substance. Steroid tablets may also be administered by mouth or in feed, if necessary.
Removing the horse from the causative agent is ideal, but as discussed above, this is difficult as it is often impossible to identify the agent.
Vigorous exercise may help to reduce the reaction. This is particularly useful in horses where other treatment methods are unavailable.
Antigen desensitisation, or ‘self-vaccination’, is a costly process with very variable results. There is little scientific evidence for its use.
Anti-histamines are expensive and generally produce only poor results.
If all else fails a complete change of environment and placing the horse on an exclusion diet of hay and grass only,
may be the solution.
