Cyara,
The earlier the better. I almost lost my bitch(bit by a young rattler) when the pups were a couple of weeks old so they probably started a bit early at 4 1/2 weeks. Had them in with the goats, but in a separate pen. By the time they were 8 weeks old they were in with the goats full time.
Ideally 6 weeks, but 8 weeks will do. Just keep them separate to start until they get used to your livestock.
Their sire Buster kept them in line. I just did the collar training which is a must along with basic obedience training(helps when it's time to get shots or spaying/neutering, or....) Just be patient on the obedience training-these dogs don't take to being man handled-slow, easy and firm is best.
Read, read and do more reading and ask questions every chance you get to someone your way with LGD's.
It's a human learning curve as well as the pups.

Will make another note here, if you can, hold off on spaying/neutering until they are a year and half old. This will allow for their bodies to mature sufficiently and to gain the bulk needed when duty requires.
Some would disagree with me, but when you have big and bad for them to deal with, they need every advantage you can give them until you can lend them a hand. Hungry, hurt predators will ignore
common sense and your dogs will have to deal with it.