Confinement feeding systems are widely used on commercial dairy farms where rations are offered as Total Mixed Rations (TMR) consisting of combinations of concentrates (protein, energy and mineral-vitamin premixes) and forages. Economic condition caused by low milk prices and narrow profit margins challenge dairy farmers to find ways to increase farm profitability in order to stay competitive (Muller and Fales, 1998). In addition, environmentally-friendly practices have resulted in an increasing interest in pasture-based dairy farming.