With rats at a farm, the rats will know where the food is already, and if you look around there is likely to be several place's (what i call hot spots) so watch out for these's place's, if there is grain around the farm spread some of this "near cover" at these's hot spot area's, ----------any bait you use, must be so they cannot pick it up and run off with it.
Some times putting different bait down the night you intend shooting it at a farm, the rats can be suspicious of it and therefore leave it that night, --------get a waste re-cycling place where all kinds of food are there and this isn't a problem as its normal food to them , peanut butter is good.
Dave (warbucks)