If you stick to the path, you'll naturally get it. The path starts when you work at the farm. After you hit the first milestone (I believe you must have willpower lower than 85 or something similar), you start getting milked when you go there. Stick with it some more, and you'll progress to automatically going to the farm every morning. Once you reach that stage, your intelligence must get very low (30 or so, although in future releases it might change to 60), and after you have gone a minimum of 2-3 times to the farm, you'll become a fully fledged cow, which includes getting branded.
Viewing post in Caliross, The Shapeshifter's Legacy comments
Some of the quests do unlock as you advance in chapters, yes. The general rule for advancing chapters is completing a Shapeshifter's temple, and then going to your study to update your notes (this is to avoid getting caught off-guard by the start of a new chapter). For the first temple, you must talk to Alpharius, your uncle's friend. In one chapter, there is another objective to take care of, but generally you just need to complete a temple and find a clue for where the next one might be.