The Witcher[]
Cow's milk is a non-alcoholic beverage, providing some endurance regeneration for 9 minutes.
The Witcher 3: Wild Hunt[]
Cow's milk is a medium-quality food and drink item in The Witcher 3: Wild Hunt, and is also needed as a component for crafting tvarog runestones with the Hearts of Stone expansion.
It is quite common as loot and can be purchased from most innkeepers.