I just found a registered Guernsey 3 year old cow who will calve in March for sale for $750. She is bred to a reg. Guernsey bull. She was a wonderful milker last year maxing out at 10 gallons a day. The guy who owns her seems really nice and is someone who is getting out of the dairy business. My parents and us want to go in halves on her and share the milk. Everything sounded perfect until I asked why so cheap. He said she was the only cow he had that the auction would not take. So I asked why. He said that all of his cows (70 head) were tested for Johnes disease. She was the only one who came up positive, but he immediately had two more tests done and they both came back negative. The auction still would not take her so he said he would sell to me much cheaper than normal. Most of his heifer calves sell for $1300. My question is could the first test be a mistake? How accurate are they? Is this something I should be concerned about? What should I do? I really want a milk cow and she sounds perfect except this one thing. I don't have any cows so there is no concern for her infecting anything I have except maybe sheep? Can sheep catch this or get something else from being around her?