Every ambitious farmer is interested in maximum yield from their flock and animals with superior qualities. From a dairy cow, a farmer is basically looking for the highest milk yields and annual calvings. To achieve this, some of the considerations a farmer looks at include animal size, longevity, fat production, udder characteristics and milking aptitude among other needs.
The goal of a cattle farmer should be to only have the best performing animals. To achieve this goal, a farmer selects those with desirable qualities and culls (get rid off through slaughtering) weak ones.