Providing a readily available water supply to all locations is an important consideration. The most common basis for grouping cows is the level of milk production. The level of production will vary with the stage of lactation, genetic potential of the herd, and the breed of the herd in question. Some herds are simply divided on the basis of stage of lactation, with the common grouping being early, mid or late lactation. Grouping only by stage of lactation ignores the cow that may have the genetic potential to continue producing at a high level into mid or even late lactation.
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.