I am not sure whether this has been suggested yet but

im just going with what i think would be useful because i personally have been looking for a lioness with 1 or 2% fertility and i know some people try to have a pride with godess fertility. And using the search in sales isnt effective as i could search '1% fertility lioness' and it will show me 19% fertility

I think having an option where we can choose fertility will be very helpful.

Suggestions are appreciated.