Lice are the most active durring the change from winter to spring, thats when they mke the trip from the head to the tail to lay their eggs. I use Eprinex pour on and dip the lower 8 -10 inches of the tail in diesel fuel. Dont laugh to loud, it works. I got it from an article written by a group of cattlemen from Florida, said they had done this for years with good results. The thinking makes sence, kill the eggs, no adults. Only one word of advice, Do this on a cold day when you can stand to wear a rubber suit and safety glasses. No will get nasty!