here - Australian College of Veterinary Scientists

The allergens used for equine skin testing tend to be the same that is used for small
animal testing, and often allergen selection has occurred with small animals in mind.
Additional horse-specific allergens such as Culicoides are also included for the equine
tests. Where horses are housed in the same metropolitan area, it is assumed that
exposure to similar allergens as small animals will occur. However, modifications to
the allergen selection may be necessary for horses from more distant country areas.
It is not apparent whether particular allergens are relevant in horses, as their lifestyle
may prevent significant exposure to various substances; such as insects (cockroach),
House-dust mites and pollens from fodder materials brought into the area rather than
grown in the area. Testing with epithelia (from other animals and humans) is not
possible in Australia due to quarantine regulation against the importation of such
allergens, so the significance of these is unknown in the Australian context. In one
study in affected horses, positive intradermal test reactions to epithelia were seen in a
significant number of clinically affected horses (54.2% to human dander!)(2).
Allergen mixes are available, but testing with these is not recommended (1), as the
concentration of the individual allergens in the mix becomes too dilute for detection.
Variation in species of insect and pollen allergens may also be important. The
Culicoides extract available through Greer laboratories is derived from Culicoides
nebiculosis. In Australia, Culicoides brevitarsis is considered to be the only relevant species
of Culicoides (at least in NSW, according to entomologists at the Elizabeth Macarthur
Agricultural Institute - pers comm.). Information from Greer suggests that crossreactivity
across most species of Culicoides can be expected, but the reality of this
assumption is not known.
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ACVSC Proceedings Dermatology Chapter Science Week 2005