Can't help with the other questions - I'm a sheep guy myself. I use intensive rotational grazing for them, but not in a dairy context. I have asked one of my seasonal grass dairy neighbors to respond to your question about mastitis. I'll forward his response to you soon. Vaccines have produced limited success as preventatives, but not for treatment.
Surgical removal is recommended if the warts are sufficiently objectional.
Merk's outlines a method to make a killed vaccine when the disease is a herd problem that is used in a calfhood vaccination program. Suggest you look over this information as it is much more detailed, and consult with your veterinarian for specifics. Soon after grazing, a plant produces much new leaf from reserves in the crown or roots, ie not all comes from photosynthesis. Cows left in a paddock for more than say 24 hours tend to backgraze this regrowth.