What is scratch grains and when to use it?

[Altairsky]

I'm restocking my chicken supplies and I came across these scratch grains https://www.tractorsupply.com/tsc/product/dumor-5-grain-scratch-poultry-feed-supplement-40-lb. I have 5, nearly 7-week old chicks and aside from chick starter/grower crumbles, grit, mealworms and the bit of forage they get inside their run (working on being able to free range, just not there yet) they haven't had much. When and how would scratch grains be fed . . .as a treat, as supplement when forage is low, . . . .?

It's extremely poor quality scratch. Why on earth do they add preservatives to seeds?

 

[redinator]

It's extremely poor quality scratch. Why on earth do they add preservatives to seeds?

That why I'm ask before getting anything new and wasting money or overfeeding "junk" food.

I know what to avoid in my dog's food, but I'm still figuring out what's right for chick(en)s.