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Beef Species Symposium: Difficulties associated with predicting forage intake by grazing beef cows

Sam W. Coleman, S. A. Gunter, J. E. Sprinkle, J. P. S. Neel
Journal of animal science 2014 v.92 no.7 pp. 2775-2784
beef, beef cows, databases, diet, energy density, equations, feed intake, grazing, lactation, models, pastures, physiological state, prediction
The current NRC model to estimate DMI is based on a single equation related to metabolic size and net energy density of the diet; this equation was a significant improvement over previous mod¬els. However, observed DMI by grazing animals can be conceptualized by a function that includes animal demand, largely determined by metabolic or linear size, physiological state, genetics, or any combination of these. Even in the database used to generate the current NRC equation, DMI by cows is poorly predicted at the extremes. In fact, across a wide range of actual DMI, predicted DMI is rather flat, indicating an insensitivity of prediction, so the model requires further refinement. A broad-based database was developed that includes pasture and confinement studies with growing, nonlac-tating, and lactating cattle. New equations are presented