… too much corn or scratch can make them obese. The layer feed is formulated to provide everything they need to be healthy and lay eggs. Adding anything else reduces the amount of layer feed they will eat and that starts to knock their diet out of balance. Short term this is not too much of a problem but over weeks and months it can cause a build up of fatty deposits in their body...
Not only the fatty deposits bad on a chickens' liver but these deposits of fat can and do lead to hen deaths because of egg Peritonitis. The reason for this is because hens (and roosters to) carry most of their body fat around clustered around their vent or egg laying opening. The result is trouble forcing the eggs out of the body and often this can result in an egg being broken inside of the hen.