Are you sure you are dealing with Leucosis, and not Johnes? There are lots of clean sources for leucosis, not too many for Johnes. IMHO, you control it by culling it...how you want to approach it is your choice. Nobody buys a cow with 'cancer eye' for slaughter anymore.
My vet says it's BLV.No cancer eyes.I have lost a few every year from this.They don't show a thing until it's to late.They go down and never recover.Very frustrating.The disease is transfered by blood and collostrum.I change needles between each animals injection and never put a dirty needle into a bottle in hope thatI could cut down on spreading the virus but testing shows sporadic results.I would buy replacement heifers and bulls from a clean herd if that was possible but I can't find anyone that tests for BLV.My vet says that some of the largest seed stock ranches test positive and it would wipe them out if they had to test and cull every animal that test positive.Every cow that tests positive doesn't die but is a carrier.I'll bet almost every herd has some cows that carry this virus whether we want to admit it or not.Very frustrating.
Since we're dairy, we don't feed any colostrum from KNOWN Leucosis or Johnes cows. I don't know what part of the country you're 'drifting' in, but the west seems to be more open to testing...I didn't say they were more honest. When Carnation Farms was still in existence, they went on an all-out program to eliminate Leucosis...5 years later they still had a 15% infection rate in the youngstock! Like anything else, it's better to be lucky than good.
Drifter, what breed? And how far from PA are you I think there is a few herds Small Show herds that are testing. But large scale it's just not that important, johnes is far more distructive, most of "us" dairy farmers already take precautions to prevent/ slow BLV.