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 countries. 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 grazing 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 depends 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 of an interruption in the feeding. For this we propose to use a simulation model 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 use an area allocation decision rule that depends on the turnout date rule and not the converse. We therefore proposed another turnout date rule based on the available herbage per ha and we calculated the area to allocate on the basis of this turnout rule. (C) 1999 Elsevier Science Ltd. All rights reserved.