ABSTRACT
One of the most important concepts defined in this publication is that feed nutrient values are not static, but change with level of feed intake and rate of passage. The Dairy NRC model was used to examine feed nutrient values for dairy cows producing 35 or 55 kg of milk per day. The same total mixed ration (TMR) was fed in this example. A 680-kg dairy cow producing 35 kg of milk per day had a predicted dry matter intake (DMI) of 23.6 kg. The net energy (NE)-l value for the TMR was 1.67 Mcal/kg of dry matter (DM). Rumen degradable protein (RDP) was 9.9% of total DM. The cow producing 55 kg of milk had a predicted DMI of 30.2 kg. The TMR had an NE-l value of 1.58 Mcal/kg of DM. RDP was 9.6% of total DM. In this example, the same TMR had a 5% lower energy value when fed to the higher-producing cow.
