like the title suggests, why not just make a little gender symbol in stable page for each pet, and just have it randomized, lets say Jeffs abbadon is a female, while
Ahmed abbadon is a male. just to make it randomized because i have seen some drama queens acting like "omg my pets are all nonsexual, eeeeeeeeeeek"
and mabye further along down the road for AL, you can have a breeding things with pets, like, glaician+slag=breezaga or mabye a clyde+george=amy thing