Growing feed has a very low calcium content for the young chickens as their kidneys cannot tolerate very much and they do not need it. Layer ration has a high calcium content because this is the material used to make the egg shells. If layers do not get the calcium in the feed, it is taken from their bones causing osteoporosis which can be fatal over time. When your pullets reach about 5-6 months of age, if you will supplement the natural daylight with light bulbs to maintain at least a 17 hour day, you will be very happy with the extra eggs.
Birds have a gland in the eye that controls reproduction.
That, of course, is egg production. This switch is turned on and off by the hours of light the birds have each day. Production decreases or stops in the fall because the daylight hours are shorter. So to maintain good egg production all winter, make sure the light never decreases. Medication Grown hens seem to have outgrown most of their childhood diseases and do not have too many problems.