The Pathology of Equine Gastrointestinal Disease

To initiate the study a comprehensive review was made of the available literature relating to the equine gastrointestinal tract. This is presented in the literature review. It includes papers and texts concerning the anatomy and function of the equine gastrointestinal tract as well as causes of clinical disease and pathological lesions. A total of 213 horses, ponies and donkeys underwent a full post mortem examination by Glasgow University Veterinary School Department of Veterinary Pathology in the the 5 year period 1987-1991 inclusive. The majority were mixed breed pleasure animals rather than pedigree competition horses. These findings are presented in Part I, the Necropsy Series. The lesions recorded were considered, on the basis of appearance and clinical history, to be either principal or incidental and were then grouped by the system in which they were found. Lesions were identified in all anatomical systems. The gastrointestinal system was found to be by far and away the most frequently affected by both principal lesions, ie those considered to have resulted in the animal's death or humane destruction, and incidental lesions with no reported history of associated clinical disease. The Necropsy Series identified 92 animals with one or more lesions of the gastrointestinal system which were studied in more detail. These findings are presented in Part II, the Gastrointestinal Series. Here the general groupings used in the Necropsy Series were broken down by location and the actual lesion identified. In addition, other factors such as possible seasonal incidence and any concurrent, contributory lesions were also studied. Grass sickness was the most frequently identified significant primary condition and parasitism featured heavily as a cause of incidental lesions. The Gastrointestinal Series in turn revealed a group of 20 animals with clinical evidence of malabsorption and a chronic enteropathy which were studied in depth. Histopathological examination of multiple tissues from these cases allowed them to be divided into 2 groups, one of recognised conditions where a definitive diagnosis was made and one where only a morphological diagnosis was made. This series is presented in Part III, the Enteropathy Series. The recognised conditions identified by the Enteropathy Series were alimentary lymphosarcoma, equine granulomatous enteritis, equine eosinophilic enteritis, cyathostomiasis, Phenylbutazone toxicity and coccidiosis. However, these 6 conditions only accounted for 11 of the 20 animals. Eight of the remaining 9 animals had gastrointestinal lesions which differed significantly from those previously described in the equine literature. These were the animals where only a morphological diagnosis was made. The remaining case had clinical evidence of malabsorption in the form of an abnormal oral glucose tolerance test result but apparently no significant gross or microscopic lesions of the gastrointestinal tract, just extremely abnormal dentition. The Enteropathy Series revealed that the recognised equine inflammatory bowel diseases do occur in the UK and are not restricted to Standardbreds and Thoroughbreds as the available literature would suggest