Calibrating a diet selection model for sheep grazing rangelands
McFarland, A.M.S.; Kothmann, M.M.; Blackburn, H.D.
Agricultural Systems 39(4): 361-386
ISSN/ISBN: 0308-521X DOI: 10.1016/0308-521x(92)90075-y
The objectives of this study were to simulate diet selection by sheep grazing on rangelands and to explore how changes in forage harvestability of different forage pools may affect diet selection. This was done by calibrating linked forage dynamics, diet selection, and sheep production models for three sites in the Edwards Plateau region of Texas. The forage dynamics model simulated the accumulation, removal, and quality dynamics for 33 different forage pools. Harvestability, preference, avoidance, and palatability parameters were associated with each forage pool through the diet selection model. The sheep model was used to calculate intake and to set grazing pressure. Diet selection was adequately represented by the models on each of the three sites. Interaction of forage quality and availability resulted in complex diet selection responses that were strongly tied to seasonal forage dynamics. Sensitivity analyses on harvestability emphasized periods when supplementation may be necessary due to restricted forage availability. The linked models provide an aid to understanding the relationships between forage dynamics and diet selection, especially when used in conjunction with field studies.