There is no way to know for sure since the cows cannot tell us, however, we do know that cows that have udders full of milk will willingly stand to be milked. The process of milking a cow is almost the same as if a calf were suckling.
Not all cows are dairy cows. All healthy female cattle can produce milk, but not all cattle are used to produce milk for human consumption. Cows are typically considered to be either dairy cattle or beef cattle.
Hand milking is the process of milking a cow using only human hands. Hand milking is time consuming, but it is a lot cheaper than purchasing and maintaining a milking machine.
Machine milking is where four vacuum-like tubes are attached to a cow’s teats to mimic the hand milking process and extract the milk.
It does not hurt a cow to milk her any more than it hurts when her calf would drink milk from her naturally.