I use ivermectin pour on for cattle. There is a great deal of information about it, including the number of days it is effective against various parasites, but nowhere to be found is the time to allow between treatments. Time frames for effectiveness vary from 14 to 56 days, with 28 days for flies, the most visible pest it controls. It also gives a 48 day withdrawal period before butchering for human consumption. Does anyone know how often treatments can be made on beef cattle?