Optimizing rotational grazing in sheep management systems

Rotational grazing on sheep farms was modeled using an iconic simulation mo deling package. An event-driven modeling approach allowed the simulation of individual paddocks on a farm and their grazing. It permitted the effects of different levels of herbage allowance to be tested and measured with res pect to pre- and post-grazing herbage mass, rotation length, diet quality, animal performance, acid the enterprise gross margin. Validation of the mod el against three experimental data sets indicated a good fit. A genetic alg orithm was implemented to enable the optimum sequence of control and state variables to be determined for the grazing system. This was used to calcula te the optimum stocking rate and monthly sequence of herbage allowance, nit rogen application, winter supplementation, and lamb drafting weight for 12 months on a theoretical farmlet. The farmlet was stocked with 17.5 sheep (e wes)/ha at an initial liveweight of 55 kg, a starting pasture dry matter co ver of 1500 kg/ha, and 130% lambing. Pasture allowances suggested by the op timization were consistent with the recommendations provided to sheep farme rs, while nitrogen applications were higher than expected, reflecting the p revailing high lamb prices compared to the cost of nitrogen boosted pasture . (C) 1999 Elsevier Science Ltd.