A model to find and test decision rules for turnout date and grazing area allocation for a dairy cow system in spring

Use of grazing is decreasing in dairy cow systems in many European countrie s. However, pasture has a lower production cost than most conserved forage. Furthermore, agronomic decision rules are available to provide dairy cows with sufficient quality and quantity of dry matter. The decline in use of g razing is partly due to organisational difficulties in planning the grazing period. Land use at the farm level requires that this plan must be made in September, about 6 months before the turnout date. This area planning depe nds on the decision rule used for the turnout date. So we propose to search for a combination of area planning and turnout decision rules that allows a dairy herd to be fed in the spring by means of grazing without any risk o f an interruption in the feeding. For this we propose to use a simulation m odel combining a grass growth model and a model for scheduling the farmer's decisions. A test of a turnout date rule showed that it is necessary to us e an area allocation decision rule that depends on the turnout date rule an d not the converse. We therefore proposed another turnout date rule based o n the available herbage per ha and we calculated the area to allocate on th e basis of this turnout rule. (C) 1999 Elsevier Science Ltd. All rights res erved.