Predicting livestock intake energy at different grazing strategies using agent-based modelling of livestock

Developing an optimal grazing strategy for livestock in spatially heterogeneous vegetation is essential for the animal production. An agent-based model (ABM) is a spatial explicit simulation modelling that predicts the internal state of livestock (e.g., metabolic energy) and external environment (e.g., plant biomass) that influence livestock movement through space. In this study, we used an ABM to predict the effects of various spatial grazing patterns of Mongolian livestock on intake energy. In the ABM, sheep acted as the agent and, vegetation was represented by the environment. The environment (approximately 8 × 8 km) was divided into 976 grid cells; the plant parameters in each cell, such as species composition, biomass, nutrition value and palatability, were measured. The movement pattern of Mongolian sheep is either voluntary or controlled by herders. The voluntary movement pattern was determined by GPS-tracking the actual movement of sheep. For the herder-controlled movement of sheep, we simulated three types of herder strategies by moving the sheep to a neighboring cell with the maximum or relative (probabilistic) high values of (1) biomass or (2) palatability or (3) nutrition of grass on the model. The metabolizable energy intake of sheep was estimated by determining the intake mass × metabolizable energy content of plant × palatability in each cell. The final energy intake of sheep were estimated after 2 months of simulation in summer at three different stocking rates. The energy intake of the freely grazing sheep was intermediate or less than that of the sheep controlled by herders in the maximum and probabilistic movement pattern of the agent, respectively. The biomass-oriented movement strategy was the best grazing strategy. Moreover, the grazing distribution resulting from the application of biomass-oriented movement strategy was spatially dispersed even the stock density was doubled. The best grazing strategy for animal production and grazing distribution is the semi-arid Mongolian grassland would be that herders move their sheep to patches with the most abundant plant biomass.