Food allergy in the horse

Abstract

has been described. 6,7 This case had features of cholinergic and food-related exercise-induced anaphylaxis. In spite of extensive searches, other reports of cases of food allergy in the horse in the peer-reviewed literature have not been found. Although it is commonly held that high-protein feeds may cause the development of cutaneous papules, giving rise to the terms ‘feed bumps’, ‘sweet feed bumps’, ‘protein bumps’ and ‘humour spots,’ the association is rarely authenticated. The concept of protein concentration in the diet eliciting an urticarial response is certainly at odds with knowledge and experience in other species, where exposure to even small amounts of the offending allergenic protein results in a type I hypersensitivity response. However, reducing the plane of nutrition appears to result in resolution of lesions in some animals. It is interesting to speculate whether the adrenergic and cholinergic systems in horses at peak fitness may modify the immune response to other environmental allergens, unmasking a hypersensitivity otherwise subclinical in nature. Certainly psychological factors (stress) were found to contribute significantly to the disease in 35.5% of human patients with chronic urticaria. As in other species, confirmation of the diagnosis of food allergy in the horse requires the feeding of an elimination diet, documentation of resolution or greater than 50% improvement in clinical signs, followed by dietary challenge to demonstrate recurrence of lesions and provocation to identify individual foodstuffs.The duration of feeding the elimination diet suggested is 3 to 4 weeks, although nothing is published to substantiate this. Equine IgE has been characterized and ELISA tests are available for the identification of allergen specific IgE employing polyclonal antisera raised in rabbits immunized with equine heavy-chain epsilon (FcF) fragments (Vetigen). However, polyclonal reagents against IgE are notoriously nonspecific and may bind other immunoglobulin classes.There are no publications substantiating the usefulness of-ELISA in the diagnosis of food allergy by comparison with dietary elimination and challenge. The development of newer specific reagents may herald the advent of improved in vitro tests for the investigation of suspected allergic horses in the future. A number of other assays are offered to equine veterinarians, often using equine blood in assays optimized for human samples.Without proper validation of such assays and subjecting them to comparison with the results of food trials and provocation, these cannot be recommended.