There's a lot of horses and cattle around where I live too. No way to protect them from fallout. I prefer prevention. Missile defense, border enforcement and a really rigorous terrorist profiling program at all points of entry. And, if necessary, torture captured terrorists to find out their plans. One nuclear detonation inside the US would be so much worse than anybody can imagine, stopping it is worth whatever it takes to get the job done.
Some suggestions on keeping your Livestock, Farm, Crops & Land Safe from Fallout are here...
http://www.radshelters4u.com/index3.htm#7