Mice are attracted to food and water . . . they also need a good habitate to get around homes/garages/buildings . . .
If you aulter their habitate, they will move on . . .
Keep all grass cut short around buildings
Keep landscaping shrubs trimed up and don't use berry type landscaping plants that could pose a food source for rodents.
Landscape with rock or concrete around buildings - not multch or other bedding type material (they love that).
As posted above, bet bait stations around the outside of the buildings to feed them outside . . .  .
Clean up the farm yard, distroying their habitate and they will live in the fields / fence rows where they belong.