The basics of drug calculations:
Dose per weight, so if 1 tube is for 1200lb animal, you would divide the grams/mg by 1200, which would give you the grams/mg/micrograms per pound, then multiply that by your body weight. Now, the hitch to this is, is the dose grams, milligrams, micrograms per kilogram or lbs, the same for animals as it is for humans?