I like the challenges to be honest, but I think they need some improvement in the requirements/rewards.
I hate being flooded by incest/old age animals when I am looking for a nice breeding pair or a partner, just because people wanted to get as many rewards as possible. Just set a maximum amount of animals that need to be released per player, and make sure the players know about how many they need. After the challenges so far I guess you have some numbers to predict how many people participated, and how many animals that would be on average per player - and to scale the over all amount to that, I assume there are a lot of people who breed hundreds.
Also the CC is a nice thought - but 150 CC for an animal that was hard to reproduce and for which it took ingame years to get to that point?
Set that margin of CC up, or get rid of the CC as a reward, and replace it with animals of decent stats. Some might want or need this very animal they got, and if not, they can sell it to buy another one.