I'm gonna give you 3 TIPS , which are not covered in ARK-Wiki :
1- Eggs weight 50 , so take care, because for stealing the egg you have to act fast.
2- For getting the Milk, beside knocking out female Wyvern, killing an Alpha Wyvern with Rocket launcher will give you lots of Milk.
3- You can't put the Milk in the fridge. Use preserving salts.
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.