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 curren t rearing conditions, the economic optimal rearing policy resulted in an av erage accounting nutrient surplus of 51.4 kg of nitrogen and 17.0 kg of pho sphate per heifer per year. To study the sensitivity of the optimal rearing policy to environmental mea sures as the Dutch mineral accounting system (MINAS), the model was extende d with the mineral accounting relationships and a 'least mineral' ration fo rmulator. Optimal rearing policy, in terms of growth rate and breeding deci sions, was only slightly influenced by these measures. The effects on ratio n composition and nutrient surpluses were considerable.