Dou Zhengxia, Knowlton Katharine F, Kohn Richard A, Wu Zhiguo, Satter Larry D, Zhang Gangya, Toth John D, Ferguson James D
Center for Animal Health and Productivity, School of Veterinary Medicine, Univ. of Pennsylvania, 382 West Street Road, Kennett Square, PA 19348, USA.
J Environ Qual. 2002 Nov-Dec;31(6):2058-65. doi: 10.2134/jeq2002.2058.
Phosphorus (P) surplus on dairy farms, especially confined operations, contributes to P buildup in soils with increased potential for P loss to waters. One approach to reduce P surplus and improve water quality is to optimize P feeding and improve P balance on farms. Here we report how varying P concentrations in lactating cow diets affects the amount as well as the chemical forms and fraction distribution of P in fecal excretion, and the environmental implications of this effect. Analysis of fecal samples collected from three independent feeding trials indicates that increasing dietary P levels through the use of P minerals not only led to a higher concentration of acid digest total phosphorus (TP) in feces, but more importantly increased the amount and proportion of P that is water soluble and thus most susceptible to loss in the environment. For instance, with diets containing 3.4, 5.1, or 6.7 g P kg(-1) feed dry matter (DM), the water-soluble fraction of fecal P was 2.91, 7.13, and 10.46 g kg(-1) fecal DM, respectively, accounting for 56, 77, and 83% of acid digest TP. The other fecal P fractions (those soluble in dilute alkaline and acid extractants) remained small and were unaffected by dietary P concentration. Excess P in the P supplemented diets was excreted in feces as water-soluble forms. A simple measure of inorganic phosphorus (Pi) in a single water extract is highly responsive to changes in diet P concentrations and hence can be indicative of dietary P status. A fecal P indicator concept is proposed and discussed.
奶牛场，尤其是封闭式养殖场的磷（P）过剩，会导致土壤中磷的积累，增加磷流失到水体中的可能性。减少磷过剩和改善水质的一种方法是优化磷的投喂并改善农场的磷平衡。在此，我们报告了泌乳奶牛日粮中不同磷浓度如何影响粪便排泄物中磷的含量、化学形态和组分分布，以及这种影响对环境的意义。对从三项独立饲养试验中收集的粪便样本进行分析表明，通过使用磷矿物质提高日粮磷水平不仅会导致粪便中酸消化总磷（TP）浓度升高，更重要的是会增加水溶性磷的含量和比例，而水溶性磷在环境中最易流失。例如，日粮中磷含量分别为3.4、5.1或6.7 g P kg⁻¹饲料干物质（DM）时，粪便磷的水溶性组分分别为2.91、7.13和10.46 g kg⁻¹粪便DM，分别占酸消化TP的56%、77%和83%。其他粪便磷组分（可溶于稀碱和酸提取剂的组分）含量仍然较少，且不受日粮磷浓度的影响。添加磷的日粮中过量的磷以水溶性形式随粪便排出。单次水提取物中无机磷（Pi）的简单测定对日粮磷浓度变化高度敏感，因此可指示日粮磷状况。本文提出并讨论了粪便磷指标的概念。
