A survey of the highest producing herds in the United States revealed that over 67% of producers used a TMR feeding system, and that these producers averaged 2.9 groups of
cows that were fed 2.7 times daily (Jordan and Fourdraine,1993). Several researchers have examined various grouping strategies and suggested that cows might best be grouped by nutrient requirements (Sniffen et al., 1993). Williams and Oltenacu (1992) compared seven grouping strategies using a simulation model that included required nutrients per kilogram of DMI, DIM, test-day milk, dairy merit, and merit weighted by DIM. Grouping systems based on nutrient concentrations were most effective in maximizing return over feed costs, whereas the method based only on test-day milk was least effective.