Me and my father were watching 'How it's made-Remix' and they showed us the exact process to extracting cows of their milk by machine. My father had then said and quote, "what people don't think about is that those cows need their milk for their babies" (unquote),and that made me think, 'yea, what about their babies?', then I thought, 'well, the factories where the cows are harboring...they really don't let them mate I guess, so how would they have offspring or reproduce if they're primary use is milk...then again, if a cow dies then there'd need to be a backup (in other words)...so'. But yes, what does extracting the cows of their milk daily do to a cows body, and the females efficiency to having offspring?
Immediately after birth cows produce colostrum which can not be sold as milk so this is given to calves. After they start producing regular milk calves are weaned and switched to a formula. Since milk is a valuable commodity as little milk as possible is given to calves with the rest made up of cheaper sources of protein and calories including blood from cattle slaughter. Cows do not continue to produce milk indefinitely; they have to be impregnated every year in order to continue to produce. Dairy cows have been selectively bread to produce several times more milk than a calf would suckle. Since cows are more valuable than bulls most male calves are killed and rendered. Cattle naturally live 20-25 years but the stress of high milk production wears them out in 5.
The cow produces enough milk for feeding as well as for production, but there are a few different answers to this.
Not all calves are left to live - they are slaughtered young and sold as veal, thereby leaving the cow to milk without having to continue feeding. Also, many calves are bottle fed - they are just given the milk that is expressed from the cow in the factory.