Not sure what type of ants we have but they are definitely a biting variety and are all over the pasture. What products are suitable to get rid of them and does the pasture need to be rested or are there grazing safe products?
Extinguish Profrssional ant granules. A granular product which is an insect growth regulator (IGR). It prevents ant larvae from maturing to new ants and the ant colonies die off. Spreading rate is so minimal that foraging ants will carry all the product back to their nests within an hour. Horses can continue grazing as the granulrs have no poison, just IGR.
I spread it at the application rate of 2 pounds per acre two to three times a year, The third time is just around the perimeter of my farm to handle new ant colonies that have spread slowly inside the the pasture fences from the woods outside.
It is the same stuff that the commercial pest control folks in my area use, and at least in my state requires no license to buy and use.