Why would it be gross? Breast milk is the first thing we drink, it's an almost perfect food. Drinking cow milk isn't very far fetched, especially when you keep cattle for meat. Seems like the most natural thing in the world frankly.

For a lot of human history (and even up to the present in some places), but certainly around the time cattle were domesticated, starvation was only ever just one bad harvest away. When last year they were deciding whether it's better to eat their own kids, let the kids eat them or just all die painfully together, drinking cow lactate was probably the least bad thing that happened to Grog and Grag this year.