There is an interbirth period mentioned in the zoopedia, so my theory is that they likely planed on doing this, but the feedback from the animals breeding like crazy in the Beta might have caused them to just turn it off.
If they truly wanted to make breeding more difficult they should not have set the breeding success rate at a maximum of 100%. I just annoys me to see all the females getting pregnant at the same time, all giving birth together, it taking a few years for all of these babies to mature and then all females to get pregnant again together.
Since we can slow aging in our zoos to keep them manageable, having an option to allow for females to become pregnant faster (like the zoopedia informs us) and make it so that not 100% of the mating results in babies so we have a mix of babies of different ages, would be cool.
I'm thinking of just giving some females contraceptives and alternating between them to cause a more natural mix of ages in the juveniles, because it annoys me so much

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