Johne’s disease is an infection of the small intestine that affects ruminants and other mammals; the illness tends to show up more in dairy cattle because of their longer life span relative to other animals, Heins said. Positive test results often precede clinical signs, which can take years to manifest — one of the reasons the Morris dairy staff has opted to perform regular whole-herd tests. When the symptoms do kick in, sometimes due to a stress event like calving, they initiate the onset of diarrhea and loss of appetite, followed by weight loss, weakness, and malnutrition, occasionally in rapid succession, he noted.
These days, the Morris herd numbers about 300 head and typically tests around 6% positive — just slightly higher than the national average, Heins said. But this herd offers a near-unique opportunity to take a closer look at the disease, as it’s split between organic and conventional. During the podcast, he sliced and diced the numbers to allow for the differences in herd management, pointing out that these divergences might offer clues as to how the cows that tested positive contracted the disease. After accounting for the presence or absence of Johne’s disease in the dams of each of the positive-testing cows in the herds, Heins discovered that of the 19 cows that had tested positive in this round, only five had dams that had also shown clinical levels of the Johne’s antibodies in their ELISA milk tests, which could explain those instances of infection.
But curiously, none of these cows with infected dams were part of the organic herd. “Something was alarming in that,” Heins said, and he decided to look into a previous calf-rearing study performed on the organic herd. He discovered that six of the seven organic-herd cows that showed positive in their 2025 tests were raised in a dam-rearing environment in group housing. Because their mothers had been cleared during their own Johne’s disease tests, Heins wondered if the calves were taking advantage of the group housing to steal milk from another cow or cows that had tested positive.
“That has really driven the point home for me,” he said. “Maybe if you’re raising calves on cows, you really need to watch for Johne’s in that herd.”
Heins also referenced two previous studies on Johne’s disease; both looked at genetic components surrounding the heritability of the illness, and both found negative correlations which suggest that cows with higher genetic merit for longevity and profitability show greater resistance for Johne’s disease. Indirectly, selection for net merit and productive life may be contributing to a slow reduction in Johne’s susceptibility.
With no cure and so many obscured pathways to infection, keeping a closed herd may seem like the best shot at eliminating it, Heins said, but pointed out that the Morris herd has been closed for 20 years and still has that 6% testing positive. “If you do bring replacement animals in, they should be from low-risk herds, or you should make sure the animals test negative,” he advised. Other precautions include keeping newborns and young animals from encountering contaminated manure — including in pastures, where the etiologic agent for Johne’s disease can survive in soil for up to a year. Colostrum and waste milk are also potential sources of contamination.
Heins urged producers to test, noting that fecal evaluation is probably the most effective among the options, which also include blood and milk. “We do the milk ELISA testing about once a year for the whole herd, so I can know what’s going on and manage it,” he said. “Through better management practices and culling, over time, we have brought the percentage of positives down from 15%.”
The podcast can be found at https://moosroom.transistor.fm/episodes/episode-297.
