For that matter, SafeGuard, Ivermectin, and Tylan are all off label use too. And while reading some information in the on line Merck Veterinary Manual yesterday, I saw something that said 'Improving sanitation and minimizing antibiotic use in poultry help reduce the incidence of candidiasis. Affected birds can be treated with copper sulfate at 0.5 mg/L of drinking water, or 0.5 mg copper sulfate per kg of feed. Vinegar is used as a treatment for candidiasis at 15 mL/L of drinking water. Chlorhexidine is used for prevention or treatment at 2.5 mL/L of drinking water. Chlorine bleach at 0.1 mL/L of drinking water may help control the infection. All of these treatments lack FDA approval' So at least in the case of candidiasis (Thrush/Sour Crop), Vinegar is not FDA approved.