Most of the turkey growers that Minnesota veterinarian Jill Nezworksi works with mix antibiotics into their birds’ feed only to cope with disease — quelling a cough outbreak or easing a bout of avian diarrhea. A minority, however, also use the drugs to boost their birds’ growth and improve the conversion of feed into body mass. Some hog farmers, cattle ranchers and chicken producers do the same sort of thing. But decades of concern over the effects of animal antibiotic use on human health have boiled to the point where tighter federal regulations appear to be in the offing. The U.S. Food and Drug Administration is expected to soon release final guidelines on animal antibiotics that are expected to limit their application – on a voluntary basis — to animal health, nixing their use to goose growth.