I have used generic ivomec for several years now and don't really think I have a worm problem but don't know for sure. I went to a meeting where a feedlot vet talked and he said if you were using the generic ivomec to just save you money and do nothing. He had a lot of data to back it up so this year I bought some of the liquid gold cydedctin and used it. I ordered some injectable cydectin to use on calves and heifers too.