The pathology of neonatal enteritis in calves with observations on E. coli, rotavirus and Cryptosporidium.

The mucosa of the small intestine of neonatal calves responds in a similar way to a variety of infectious agents. However, samples should be removed under general anaesthesia to avoid post-mortem artefacts. These include the separation of epithelium from the villous lamina propria and denudation of villous tips within a few minutes of death, and occur more rapidly in challenged animals. Pathological changes consist of blunting and fusion of the villi with a reduction of the columnar epithelium to cuboidal and occasionally squamous epithelium. A surface inflammatory exudate may be present, especially within 24 hours of challenge with enteropathogenic E. coli. Examination of several sites from the small intestine indicates a variable distribution for enteropathogens. Rotavirus is seen by immunofluorescence microscopy in epithelial cells principally in the proximal half of the small intestine, although they may occasionally be found in the distal half. By contrast, E. coli organisms adhere to enterocytes in the distal half of the small intestine. Cryptosporidia inhabit the brush border of the enterocytes enclosed within host cell microvillous membranes, principally in the distal half of the small intestine. Examination of the small intestine of neonatal calves for pathological changes and the presence and distribution of infectious agents complements bacteriological, virological and immunological techniques in the diagnosis of neonatal enteritis.