The management of pastoral grazing systems under biological and environmental variation

Abstract

Abstract The demand from meat processors that pastoral farmers supply animals at an agreed time, and to agreed specifications (e.g. carcass weight), requires formal consideration of uncertainty and variability in feed planning. This paper develops this theme by deriving the probability distributions associated with simple feed planning models when pasture growth, initial estimated pasture dry matter and animal growth are regarded as random variables. It is shown that the probability of achieving a goal (e.g. satisfying a contract to deliver animals of a particular type at a given time), becomes an important statistic when the key feed planning variables are random. The feed resources required to achieve a goal with various degrees of certainty can be calculated, and this is demonstrated in the paper. The effect of changing variances in feed planning variables on the resources needed to achieve a goal with specified probability is demonstrated with a simple example. The options a farmer has for managing variability (e.g. feeding supplements), are discussed. It is particularly notable that smaller variances in estimates of initial pasture dry matter and pasture growth rate assist feed planning under variability.