Humans are born with about 7 million eggs but the number drops a lot by maturity. Nearly all animals have more eggs than they can use in a lifetime. It would do no good for the species if that supply was too limited. If they quit breeding earlier it's because they were too stressed physically and not because they ran out of eggs. Even in humans who ovulate monthly women don't start menopause because they ran out of eggs. It is hypothesized to be genetically predetermined. How often you can breed depends on how good of condition your does stay in. That varies between does even within the same breed fed the same diet.