Treatment of horses with chronic diarrhea: immunologic status.

All chronically diarrheal horses given (orally) 2 series of treatments with normal horse serum recovered in 2 to 4 weeks. However, mild diarrhea sometimes persisted several months in the group of horses with severe diarrhea. Weight gains were approximately 35% in horses with severe diarrhea and approximately 10% in horses with mild diarrhea. Serum specimens from 12 diarrheal and 20 normal horses were examined for immunoglobulins by single radial immunodiffusion technique. Concentration of immunoglobulin A in serum of diarrheal horses was approximately 50% lower than that in serum of normal horses. By contrast, there was more immunoglobulin G in serum of diarrheal horses than in serum of normal horses. Phytohemagglutinin (PHA-M) responsiveness of blood lymphocytes showed transient suppression during the stage of severe diarrhea. The regaining of PHA-M responsiveness of lymphocytes was observed simultaneously with the recovery process. However, the responsiveness of lymphocytes in recovered horses remained markedly lower than that in normal horses. Allergic reactions in diarrheal and normal horses were studied by observing dermal response to injections of saline extracts from some of the horse feeds. A delayed hypersensitivity reaction to streptokinase-streptodornase and PHA-M was also studied. Allergic reactions to these extracts were not induced in either diarrheal or normal horses; however, inflammatory response to the extracts was approximately 50% greater in normal than in diarrheal horses. Response to intradermal injection of either streptokinase-streptodornase or PHA-M was significantly greater in normal horses than in diarrheal horses.