Environmental impact of heifer management decisions on Dutch dairy farms

Dairy farming contributes substantially to Dutch environmental problems. A dynamic heifer rearing model was used to determine the extent to which the rearing activity influences nutrient flows on a dairy farm. Based on current rearing conditions, the economic optimal rearing policy resulted in an average accounting nutrient surplus of 51.4 kg of nitrogen and 17.0 kg of phosphate per heifer per year. To study the sensitivity of the optimal rearing policy to environmental measures as the Dutch mineral accounting system (MINAS), the model was extended with the mineral accounting relationships and a 'least mineral' ration formulator. Optimal rearing policy, in terms of growth rate and breeding decisions, was only slightly influenced by these measures. The effects on ration composition and nutrient surpluses were considerable.