Are you doing the cheep route of over the counter melatonin or the melatonin specifically used to grow hair on calves. We fed our show steer 5 tablets daily and his last show was our county fair the last week of July. He was about 1380 lb at that time. We are also giving the over the counter tablets to our show heifers. They are Junior Yearlings and we are giving 5 tablets. They have worked wonders and our much cheaper.
What size tablets are you feeding? I've seen them anywhere from 3mg to 10mg.
You need to feed about 100mg/day to see any difference. I would recommend the implants though. There's no comparison between the two. Their gonna be a little more expensive than feeding tablets, but it's worth it.