Here's a bit of info:
However, to begin producing milk, a cow must first give birth. The hormones released at birth and the sucking of the calf stimulate the cow to lactate (produce milk) for her calf. Cows produce the greatest amount of milk right after they give birth. If a cow is not milked, she will stop producing milk.
Milk is made and stored in the cow's udder, which is divided into four separate quarters, each having its own milk supply. When laden with milk, each section can be drained through one teat.
The cow produces milk on a 305-day cycle, then is "dried up" for 60 days prior to the birth of the calf. This means for 60 days of the year your cow will not be producing any milk.