Experimentally infected heifer #13 and calf

HeifHeifer #13 was experimentally infected with M. paratuberculosis by feeding it a high dose (100 million bacterial cells) in its evening bottle of milk on each of three nights. Three years later she had a calf.

At calving, heifer #13 was somewhat thinner than the non-infected control cows, but not extremely so. She developed diarrhea shortly after calving and the diarrhea persisted but was never watery. Two months after calving heifer #13 was euthanized. M. paratuberculosis was isolated from the milk of this cow and from multiple internal organs. The calf was euthanized at 5 months of age and also was found to be infected with M. paratuberculosis.
The pattern of diagnostic test results and the pathology seen at necropsy, enlarged mesenteric lymph nodes and thickened ileum are shown in other photographs.

The experimental infection in heifer #13 illustrated several features of paratuberculosis in cattle:

1. Infected animals can appear normal, eat well, and have calves.
2. In the late stage of infection, M. paratuberculosis is excreted in milk.
3. In late stage of infection, the M. paratuberculosis infection is disseminated to several internal organs.
4. Calves born to infected cows have a high probability of becoming infected, particularly if they stay with their mother and nurse naturally.

Comparison of the pattern of diagnostic test results for heifer #13 to that of heifer #11 shows that the pattern varies considerably between animals. Recommendations by experts about when to test cattle for Johne’s disease by different test are based on what typically happens most of the time. Individual animals may not always fit the typical pattern.