my vet and I are going to work my first year heifers this weekend, we dicussed putting fly tags in, he told me that the flys in this area was immuned to them unless they came out with a new tag this year, said I would be wasting my money. My farther inlaw used to raise cattle several years ago and gave me a gallon bottle of lintox he said the best he could remember it worked fairly well, just wondering if anyone has ever used this product and how long will it keep the flys off. or maybe you can tell me what you use and whats its affect. also I want to thank everyone that responded to my last post. Beings I'm a newbie and all I figured no one would even respond and before I knew what hit me I had 19 or 20 all very good advise.