I think it would mainly cause issues for people buying from Frontier/new players. The infertile tag is currently used for animals that can't breed due to their age, so sterile might be better.@Kai I'm not sure I follow. Zero fertility should mean infertile with nothing you can do about it. Anything above that should be both chance to actually mate and chance to produce max amount of babies, though obviously the amount of babies would be on a different percentage like it works now.
How would it mean that they need to change their diversity genes though. Two perfectly healthy animals can still and do produce a less than healthy baby from time to time, it's just that two healthy mating animals are less likely to produce unhealthy than inbreeding animals.
Nothing needs to change other than 0% fertility means infertile. This adds another layer of gameplay where you're not always going to be able to breed.
I don't think there would be any incentive to sell sterile animals for cash on the market. Honestly, why would you even want to give new players a bunch of animals that can't breed? They need to earn some CC to buy better animals, and animals that can't breed won't help with that (they'll just cost then money via food and give nothing in return).