[samatman]

One of the local dairies has better milk, and anything derived from milk, than the others. Their secret is that some of the herd is of Guernsey and Jersey breed. Milk from only those cows is yellowish in hue, and certainly richer in fat, some would say it tastes better but it definitely tastes different. I prefer the combined milk from the dairy in question (in the US) to pure Guernsey, which is also available, depending on locale.

I would say that the effect of breeding for quantity is less extreme for dairy than for chicken meat, but it's there. The main impact on flavor isn't actually higher production by the cows, it's large-scale homogenization and high-temperature pasteurization as side effects of scale. The larger processing machines oxidize the milk more, and longer pasteurization increases shelf life but it does reduce the taste/quality further. I'm not talking about UHT, which produces a quite noticeable difference in the milk, one which some people like, just processing which leans more in that direction.