If you are going to use the Melatonin tablets, 3mg, you need to give them 33 tablets a day, this equals the dosage they recommend with grow & shine (100mg a day).
We fed them in the morning when we put the calves in the stall, counted out a whole bottle of pills and bagged them so all the boys did in the morning was put them in the feed with the other top dresses, You need to give it to them at least 90 days out, 120 is better. Rinse blow and comb, as well as keep out of the daylight.
You can put them in boluses and administer them that way daily.
If you are only giving 2, 3mg, tablet a day, you are wasting your money it will have no effect on the animal.
If you want to use it to calm them, we would start 3 days out from the show, giving 40, 3mg, tablets a day, through the show.
I like the grow & shine over the pills JMHO