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A female dog goes into heat and that is the only time it can get pregnant. Chickens do not go into heat; a laying pullet or hen doesn't get pregnant. Whether or not there is a rooster present to fertilize the egg, she will lay. Roosters don't care if a female chicken is old enough to lay eggs, and will jump a female chicken regardless of her age.
That said, there are times of the year, especially spring, when a rooster may become more aggressive with the females in your flock. A female becomes broody due to a hormonal change in her body, it doesn't matter if a rooster is present.
You don't need a rooster unless you want fertilized eggs for hatching or eating.
Your girls may be happier without the stress of having a rooster around.