Breeding Help

I have been playing my current sandbox game for about 15 hours and so far I haven't managed to breed a single animal. They all have high stats for their needs, plenty of enclosure space, but not one set of animals is giving me any offspring. For the animals who are social I have the correct balance of male to female but it still isn't working. No one is on contraception either. Is there a setting I'm missing? Am I just being extremely unlucky? Completely baffled as I've played campaign mode and managed to do it previously. Any help would be appreciated!