Some dairymen use a combination of factors when grouping their herd. First lactation cows may go in the same group, and fresh cows may be placed in the top producing group and left there as long as production remains above a certain level. These and other factors may be combined to facilitate an orderly system of grouping. Regardless of what factors are considered in grouping cows, it is important that cows be in groups with similar nutritional requirements. The factors influencing nutritional requirements of lactating cows include milk production level, fat percentage of the milk, body weight of the cow and age of the cow.
Age is an important consideration in first and second lactation cows.
These animals are still growing and need extra nutrients above maintenance and production for body growth. First lactation cows need to be fed nutrients at twenty percent above their maintenance requirements to provide for growth, while second lactation cows need to receive additional nutrients at the rate of ten percent above maintenance requirements. Consequently, first and second lactation cows should stay in a group higher than their level of milk indicates because of extra requirements for growth and because of limited feed intake due to smaller body size. Dry matter intake shows a gradual increase as milk production level increases. However, it should be noted that the protein and energy concentration required at each level of production increases also.