Evaluation of the National Research Council (1996) dry matter intake prediction equations and relationships between intake and performance by feedlot cattle

Intake prediction equations of NRC based on initial BW and dietary NE _m concentration were evaluated with a commercial feedlot database consisting of 3,363 pen means collected from 3 feedlots over a 4-yr period. The DMI predicted by NRC equations had significant (P < 0.01) mean and linear biases across the range of observed DMI in the database. In general, DMI was overpredicted by the NRC equations. Adjustment of the NE_m-based prediction by use of a 12% increase in NE_m concentration and a 4% decrease in predicted DMI associated with the feeding of monensin decreased bias. Dry matter intake predicted by the NE_m-based monensin-adjusted, NE_m-based, and initial BW equations explained 67, 66, and 64% of the variation in observed DMI, respectively. Relationships between ADG and G:F with DMI as a percentage of BW and NE_g intake also were examined in the same data set. Across the wide range of average shrunk BW in the database (334.4 to 548.0 kg), ADG was positively related to DMI as a percentage of BW (P < 0.01); however, this relationship was not strong (r² = 0.17). Likewise, G:F showed little relationship with DMI as a percentage of BW (P < 0.01; r² = 0.05). By accounting for differences in maintenance energy requirements of pens with varying average BW, NE_g intake was strongly and positively related to ADG (linear and quadratic, P < 0.01; R² = 0.70); however, G:F showed little relationship with NE _g intake (P -0.02; r² = 0.01). Our evaluations with measurements of DMI by cattle in commercial feedlots indicated the shortcomings of current published equations for predicting DMI and suggest the need for development of new equations with improved accuracy and precision. Furthermore, our data indicate that increasing NE_g intake increased ADG in a quadratic manner but did not affect G:F by pens of cattle in feedlots. These findings suggest a diminishing returns effect of energy intake on energy retention.