Yak are the exclusive beast of burden in the high Himalaya due to their high altitude adaptations, legendary strength and endurance, and sure footedness. They are used to carry packs, riding, and even pulling carts and plows.
In Tibet Dzo are primarily used as work animals at moderate altitudes. Full blood yaks take over above 14,000 feet. In North America the animal of choice is the steer (castrated males). Steers are like geldings in horses, they have an even and tractable temperament. Cows can be moody and intact males can be unpredictable and aggressive. Steers by far make the best pets and companions.
Pack steer training should begin at a very early age, the earlier the better. The most friendly steers are bottle raised. Keep in mind that yaks are strong herd animals and do not do well by themselves. You will need two or more pack yaks.
There are many books and videos on training oxen, these are good resources for training yaks and will give you an idea of the training techniques employed. In short, bovines do well with consistent repetition. They like a routine. Yaks are more intelligent than cattle and respond well to kindness. However, all bovines have a rough and tumble culture, the leader of the pack is the biggest bully. Donít let your yaks bully you, start early on teaching them to respect your space and authority so when they weigh over half a ton they will not even consider challenging you.
As small calves yaks are easy to train and too small to challenge you. Start by teaching them to tie, then to walk on a lead. Get them addicted to some kind of treat you can carry in your pocket. Teach them to let you handle their feet. Start them with XL dog packs to get accustomed to carrying something. But mostly, spend a lot of time with them and be kind. Once you have established trust they will do almost anything for you and will come running with tails in the air when you call them.