My chickens used to lay 5-6 dozen eggs a day, for last couple of months they are only laying 1-2 dozen. Can they be to fat to lay, they are free range and get fed layer pellets and crumbles twice a day. they seem healthy other wise and happy. They get 5 way scratch for treats and some house scraps, they are only 2-3 years old. What else could stop them from laying?