Chapuis-Lardy L, Fiorini J, Toth J, Dou Z
Center for Animal Health and Productivity, School of Veterinary Medicine, University of Pennsylvania Kennett Square, 19348, USA.
J Dairy Sci. 2004 Dec;87(12):4334-41. doi: 10.3168/jds.S0022-0302(04)73579-1.
Recent data from phosphorus (P) feeding trials have demonstrated that P concentration in dairy feces is directly affected by P levels in diets and that farm P surpluses as well as potential environmental losses can be reduced through dietary manipulation. The current study was conducted to examine the variability of fecal P under farm conditions and to elucidate factors affecting the concentration and solubility of fecal P. Feed and fecal samples from >30 commercial dairies in the Northeast and Mid-Atlantic regions were analyzed. Dietary P concentrations ranged from 3.45 to 5.78 g/kg of feed DM (DM), and P determined in acid digests (TP) of feces from 5.84 to 12.84 g/kg of fecal DM. On average, 50% of fecal TP was water soluble; of the latter, 83% was inorganic (Pi). Across-farm variability (n=33) had CV averaging 18.9% for fecal TP and >20% for Pi and total P (Pt) in water extracts. Within-farm variability based on multiple samples per herd had the same magnitude as across-farm and was independent of sample numbers from individual farms (n=7 to 30). Of all fecal parameters determined, pH and DM had the lowest variability (CV <10%), water-soluble Pi, Pt, and Ca the highest (CV of 20 to 30%), and total P, Ca, and Mg determined by acid digests were intermediate (CV 10 to 20%). Water-soluble Pi concentrations determined in dried-ground fecal samples were lower than in wet samples. The drying-grinding process changes Pi solubility and the change is not linear. This study confirms that dietary P concentration is the dominating factor affecting fecal P excretion; however, Ca concentration, DIM, and fecal pH also made small, but statistically significant contributions, although some of the mechanisms remain to be thoroughly investigated.
近期关于磷（P）饲喂试验的数据表明，奶牛粪便中的磷浓度直接受日粮中磷水平的影响，并且通过日粮调控可以减少农场的磷盈余以及潜在的环境损失。本研究旨在考察农场条件下粪便磷的变异性，并阐明影响粪便磷浓度和溶解性的因素。对来自东北部和大西洋中部地区30多个商业奶牛场的饲料和粪便样本进行了分析。日粮磷浓度范围为每千克饲料干物质（DM）3.45至5.78克，粪便酸消化物中测定的磷（总磷，TP）为每千克粪便干物质5.84至12.84克。平均而言，粪便总磷的50%是水溶性的；其中，83%是无机磷（Pi）。农场间变异性（n = 33）显示，粪便总磷的变异系数（CV）平均为18.9%，水提取物中无机磷和总磷（Pt）的变异系数大于20%。基于每个牛群多个样本的农场内变异性与农场间变异性大小相同，且与各个农场的样本数量（n = 7至30）无关。在所有测定的粪便参数中，pH值和干物质的变异性最低（CV < 10%），水溶性无机磷、总磷和钙的变异性最高（CV为20%至30%），酸消化法测定的总磷、钙和镁处于中间水平（CV为10%至20%）。干磨粪便样本中测定的水溶性无机磷浓度低于湿样本。干燥研磨过程会改变无机磷的溶解性，且这种变化不是线性的。本研究证实，日粮磷浓度是影响粪便磷排泄的主要因素；然而，钙浓度、产犊间隔天数（DIM）和粪便pH值也有较小但具有统计学意义的贡献，尽管其中一些机制仍有待深入研究。
