Do chickens always lay eggs?
In short; yes. It depends on the breed (not all lay up to 1 egg/day), the age of the bird and on nutrition. High yielding breeds of chicken are e.g. dependent on supplements of calcium to be able to produce new shells rapidly (e.g. in the form of ground-up shells). Some information on the nutrient requirements of chicken can be found at Feeding the Laying Hen. Egg production will also fluctuate over the year, and will generally decrease e.g. during molting, since energy and nutrients are then diverted to the production of feathers (see info at e.g. The Poultry site).