I can't think of a reason why you would use a medicated scratch for chickens. They usually get medicated starter, and perhaps grower, but it's not good to have chickens on medication all the time. That's why production birds on megafarms develop drug-resistant organisms. Medicate when it's needed, but not continuously.
Big places do that because the conditions they house their birds in constantly breed disease.
If your home flock conditions are poor, better to improve the conditions than continuously drug the birds. It's better for their health and ours, too. Mine turned out just fine and are now grown. I still give them game starter mixed with laying pellets. This way, they should get enough protein and my older ducks have been very healthy.