Now that you know Johnes is out there, you can be an informed buyer, what you should also know is that it is a disease that resides in the intestines and prevents nutrient absorbtion, you will see the cattle eat and eat but vertualy starve to death, there are some who believe you can keep positive animals separated and continue to raise them confinded away from the healthy herd, but they will still waist away and die.
Better to submit blood for an ELISA test and fecal culture on suspect animals, and remove any positives, this is not a controlled DZ, such as Bangs or TB, but it is very costly to the beef industry, many herds that are PB herds using Holstien females for recipients for their ET programs have Johnes, as well as Bovine leucosis, another waisting DZ that is quite nasty.
I personnaly would avoid purchases from that herd in the future, and try to buy cattle that are health tested clean befor purchase, it is very easy to have the Johnes test done at the same time as the Bangs and TB test, they use serum from the same blood sample for both Johnes and Bangs, and the TB test is just the 72 hour test in the caudal fold of the tail, which is a pain but if it is a TB free herd, then there is no time lag, or need to pull cattle up for a second reading
