When I was at "goat class" this weekend one of the speakers and just finished up a 2 year study where half the herd was regularly dewormed and the others were dewormed using the FAMACHA method. The good news was that there was a 36% reduction in cost because you are only giving it to goats that need it. The bad news is you're staring into goat eyes. A LOT. He suggested every 2 weeks. He also mentioned if it was continually wet outside you could almost guarantee they were gonna need to be dewormed. Also if you wait till the eyes are about white your goat is probably going to die.