I think how many litters you can expect depends on your rabbits' genetics and the way you manage them. Some of my brood does have 5-6 litters before I retire them, but others have far more than that. If a doe gives me outstanding bunnies I tend to rebreed her more times than does that produce fair-to-middling offspring. Black Star was one of my Champion-makers and she had nine litters. She was bred the first time at 8 months of age, and was still producing good-size litters at age 4 when her career ended suddenly as a result of a broken back.
The graph below shows her production; most of the litters in which she kindled far more than she weaned were the result of my fostering some of her kits to does with smaller litters.
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