Many peeps have many different opinions as to what to feed their chickens. Lets take bread... It is not a complete nutrition compared to chicken feed that has a balanced amount of needed nutrients, protein minerals, vitamins, etc. It will not hurt your chickens, but will act the same if you give your chickens too much scratch, or other treats. It dilutes the percentage of the needed items like protein. I do not see milk as being bad for chickens ether. Again , it offsets the balance that is more ideal nutrition.
The results, will not necessarily be sick or dead chickens. You may see less than ideal egg production results.
I do give my chickens a variety of feed as well as generous amounts of scratch, bird seeds, and other things including kitchen scraps. (never spoiled food). My chickens live long lives. 13 was oldest. Maybe I would not win any egg laying contests, but that is not important to me.
WISHING YOU BEST....and