Many people suggest kiting the poison wyverns when in need of milk, but frankly; fire wyverns breath ranged attack isn't all that great. And even if it does manage to hit your mount, it won't hurt you - unlike the poison. I always go for low leveled female fire wyverns because of this. Of course, whatever you do: **Don't go for the lightnings.**
I got a level 150 lightning egg and I was so excited to hatch the egg...that when I went to put the egg down I accidentally ate it instead. :( ps4 users: R2 ISN'T GONNA DROP THE EGG YOU'RE GONNA EAT IT LIKE ANY OTHER EGG. REMEMBER THIS. LOGIC BEFORE EXCITMENT.