MODELING DIET SELECTION AND INTAKE FOR GRAZING HERBIVORES

This paper presents a mechanistic model which simulates diet selection and animal intake. It incorporates quantitative representations for preference, palatability and availability as they affect diet selection and intake by herbivores. Preference is defined by an index calculated from forage crude protein and digestibility and a user-assigned avoidance parameter. Palatability is related to potential restrictions to forage intake by anti-quality components. Dietary restrictions arising from low forage availability are simulated using a Michaelis-Menten-type function. Inputs of forage quality and availability are obtained from a forage dynamics model, and output from the diet model goes to an animal production model. Sensitivity analyses were conducted to determine the diet selection and intake responses to variations in selected model inputs and functions. Diet selection and nutrient intake were highly responsive to changes in forage growth rates, stock density, forage availability, and the forage quality functions in the desirability index. The model provides a working hypothesis for evaluating biological cause and effect mechanisms of diet selection and intake by grazing ruminants. Additionally, the level of resolution of the combined forage-diet-animal models is appropriate to provide a basis for developing management recommendations.