I also bought some a the feed store a couple of weeks ago. Noromectin is generic ivermectin, no difference, except maybe in cost and name. Heres a little info on it.
The generic product is administered as a sterile solution, contains the same active ingredients in the same concentration and dosage form as the pioneer product, and contains no inactive ingredients that may significantly affect the absorption of the active ingredient. The pioneer product, IVOMEC Injection for Cattle and Swine (ivermectin), the subject of Merial, Ltd., NADA 128-409, was approved on February 13, 1984.
http://www.fda.gov/downloads/AnimalVeterinary/Products/ApprovedAnimalDrugProducts/FOIADrugSummaries/ucm061370.pdf
