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What is the best chicken to use for laying eggs?
There is no one right breed answer for everyone. The breeds do have tendencies but each chicken is an individual. They don’t always read the same behavioral book. Probably the best average chicken for egg laying is the Leghorn. They are fairly small so they get good feed to egg conversion. They don’t have to use a lot of what they eat for body maintenance like a larger chicken would. They generally lay a lot of eggs and those eggs are usually pretty good sized. But there are a lot of other breeds or crosses that work great. It depends on what your other goals related to chickens are.
Do the chicken's need a light in the coop?
They don't need a light, but they need light so they can see to move around and go to bed. A window provides this. It’s best not to leave a light on all the time. They really do need some dark for down time.
If you are talking about a light for heat in the winter, no, they do not need one. They wear a down coat year round. Heat in the summer is more of a danger than cold in the winter.
About how high does the nesting boxes need to be from the floor?
Whatever is convenient for you. The chickens pretty much don’t care. Some of us have nests on the floor, some have them mounted up a few feet on the wall. If you have a bad back, you might not want to bend over to get the eggs. I have two different levels, a couple maybe 14” up and one maybe 2 feet up. Right now they prefer the lower ones. I have had different chickens in the past that preferred the higher one. But they will lay in any of them.
Chickens scratch a lot. If you put them right on the floor, they might (not absolutely will, but might) scratch dirt and poop from the floor into the nests. Of course this depends on your specific conditions, what kind of bedding, if any, you use on the floor and how high the lip is on your nest.