Then slowly reintroduce the original feed. If this stimulates the appearance of hives, you can assume that the feed is the cause of the allergy. A variety of medical therapies are available through your veterinarian, with corticosteroids most commonly used. Following oral administration, remission of clinical signs is usually observed over 24 hours. Be aware that steroids may cause laminates, so don't attempt to treat the horse without first consulting your veterinarian.
Heaves is one of the most common types of allergy observed in horses.
The common clinical signs associated with heaves include a chronic cough and exercise intolerance. Horse often exhibit an increased respiratory rate, and a nasal discharge may be present. Wheezing may be audible, and over time, horses will develop a 'heave line' between the flank and thorax. Severely affected horses will suffer weight loss and appear unthrifty. Pollen, dust or molds result in allergic bronchitis that is similar to asthma in people.