How are you defining "best"? Jerseys have high fat content/better flavour ('creamier'); Holsteins produce more milk per cow.
Money producing , like cows produce milk
Depends on what breed you are referring to. Dairy cows give a lot of milk; beef cows don't.
Simple: don't milk her, and don't breed her.
Holsteins.
Cows and goats need to be fed on grass and oilseed cakes because grass and oilseed cakes are milk producing food so these help them to produce milk
Artificial Selection
None. There is no breed that gives this colour of milk. All milk from all breeds of dairy cows is white.
Holstein cattle produce more milk than any other breed, however, that does not name the breed as the best lactation. When looking for a breed or even a single cow for dairy production, it is best to research her genetics. These genetics will give you more information on how well she produces, her longevity, and an estimate of the components of her milk. Breed characteristics are only a small affect on the milk produced.
The Holstein.
You don't have to have dairy cows if you are not wanting to make money off of producing milk or want to have milk for yourself and your family. The only time you have to have dairy cows is if you are getting into a dairy operation.
This depends on what is regarded as the most desirable trait. The Holstein cow is known for producing a large amount of milk. The Guernsey is known for producing milk with a rich flavor. The Jersey cows produce milk with a very high butterfat content. Some cows, such as the Ayrshire and Milking Shorthorn are more efficient in producing milk from the amount of feed they get. There are many other breeds with special advantages, such as Indian breeds that can live and produce milk in marginal dry and hot lands.
Dairy cows, those cows that are selected for and bred to produce milk.