Nutrient fluxes and environmental performance indicators for a pasture-based dairy system

ABSTRACT. The aim of this study was to evaluate the nutrient fluxes for lactating cows in a pasture-based dairy system and the impact of a nutritional management strategy on the environmental performance indicators. Fourteen lactating cows were divided into two experimental groups with seven animals each. The nutritional managements were a diet containing 20% crude protein (Group 1) and a diet with adjusted protein (Group 2). The nutrient budget was calculated on a monthly basis for nitrogen, phosphorus, and potassium. The nutritional strategy of adjusted protein reduces the total surplus in the lactation period for nitrogen by 7.6% and for phosphorus by 6.3%. The total potassium surplus of the adjusted protein group was 8.5% higher. The average nitrogen use efficiency was 21% for group 1 and 22.7% for group 2. Phosphorus use efficiency ranged from 13.4 to 35% for group 1 and from 15.5 to 34% for group 2 and potassium average use efficiency was 14.2% for group 1 and 12.6% for group 2. Nutritional management reduced nitrogen and phosphorus surpluses as well as the values of the environmental performance indicator. Based on this, it is possible to improve the environmental efficiency of dairy systems through improved nutritional management.摘要。本研究旨在评估放牧型奶牛养殖系统中泌乳奶牛的养分通量，以及营养管理策略对环境性能指标的影响。将14头泌乳奶牛分为两个试验组，每组7头。试验采用两种营养管理方案：粗蛋白含量为20%的日粮（组1）与调整蛋白日粮（组2）。按月对氮、磷、钾的养分收支进行核算。结果显示，调整蛋白的营养策略可使泌乳期氮总盈余降低7.6%，磷总盈余降低6.3%，但调整蛋白组的钾总盈余高出8.5%。组1的平均氮利用效率为21%，组2为22.7%；组1的磷利用效率区间为13.4%~35%，组2为15.5%~34%；组1的平均钾利用效率为14.2%，组2为12.6%。营养管理可降低氮、磷盈余及环境性能指标数值。据此，可通过优化营养管理提升奶牛养殖系统的环境效率。