Pasture utilisation in hill country 2. A general model describing pasture mass and intake under sheep and cattle grazing

Abstract

A general model describing daily changes in pasture mass and apparent individual herbage intake under mob grazing was developed for future use as a component of feed budgeting within hill country farming systems. The basic concept of the model is that of a negative exponential. The exponent includes animal density, time, and a constant k - the relative rate of pasture disappearance. Where k is unknown, the model is useful in a historical sense for describing pasture mass and intake levels at intermediate stages of a grazing period. Current pasture growth and its consumption are included in the model. The model is restricted by the requirement that the combined herbage intake must exceed current pasture growth rate. In developing and understanding factors affecting k, general relationships between pasture residual mass and allowance were used. k is situation dependent, being influenced by maximum apparent intake per animal, pasture allowance, and green: dead herbage ratio. Established sets of relationships between k and allowance would allow the predictive use of the negative exponential model. General empirical relationships between individual herbage intake and pasture mass were also established for sheep and non-lactating beef cattle. These relationships are applicable for apparent intakes of less than maximum and serve as a simple guide when k is unknown or difficult to determine.

Keywords:

• models
• pasture utilisation
• pasture intake
• hill country