Gastrointestinal trichomonads in horses: occurrence and identification.

A survey of horses for gastrointestinal trichomonads was conducted to determine the organism's role in equine diarrhea and to establish its proper identity and morphology. Trichomonads were found by cultural examination of feces of 101 (35%) of 289 apparently healthy horses. At necropsy, trichomonads were cultured from 11 (37%) of another 30 horses which showed no signs of diarrhea at the time of death. In 4 of the 11 horses, colonies of trichomonads numbered 30,000 to 150,000/ml of cecal fluid. Diarrhea was induced in 1 of 6 horses, with the fecal fluid containing 10,000 to 110,000 trichomonads/ml. The trichomonad was identified as Tritrichomonas equi and it appears to be a normal member of the intestinal fauna of the horse. Its role as the etiologic agent of equine diarrhea is considered doubtful. The large numbers of T equi found in diarrheic feces are considered a response to, rather than a cause of, the fluidic environment of the gastrointestinal tract.