@johannpiber A cow can only/start giving milk after she had a calf. The calf is taken away and instead of the calf machines take over the job. The more you milk the more milk they produce. If you slow it down it will be less.
The only thing I know is they bred all kinds of cows to give more and more milk. We had the "milk lake" and "butter mountain" in the Netherlands (too much but it was never cheaper for us) now the pigs and cows have to go because of the environment (an increase of nitrogen) and more houses can be built. Happy weekend.