>>14897388People associate udders with breasts just because of the milk. Dairy cows are seen as something of a fertility symbol, since they spend most of their lives either pregnant or nursing.
It's a sad truth in reality that breast size actually isn't related to milk production in the way we usually think. Women of all breast sizes have roughly the same amount and quality of milk ducts. Women with larger breasts actually tend to have more trouble with expressing milk, as the fat tissue tends to apply compression to the milk ducts.
A woman with small breasts will typically produce just as much milk and also have a much easier time with milking. I wish there was more respect for this fact.