Kebreab E, Odongo N E, McBride B W, Hanigan M D, France J
National Centre for Livestock and Environment, Department of Animal Science, University of Manitoba, Winnipeg, Manitoba, R3T 2N2, Canada.
J Dairy Sci. 2008 Jan;91(1):241-6. doi: 10.3168/jds.2007-0432.
A major source of environmental pollution has been overfeeding P to dairy cows, caused by the "safety margins" added to diets in order not to compromise the health and production of animals. An extant whole-animal model was evaluated using an experiment conducted in Ontario to assess its applicability for predicting P excretion. The objective of the study was to use the model to estimate P excretion levels and the economic and environmental implications of implementing mitigating options by following recommendations from studies that have reported sufficient levels of P inclusion in the diet. Mean square prediction error and concordance coefficient analysis showed that the overall predictions were close to the mean and that there was only a slight underprediction of fecal P output by the model. The majority of the error was random, with only 8.9% coming from error caused by deviation from the regression line, and the model did not show a systematic trend of over- or underprediction. The model was then used to predict P excretion in Ontario by using diets commonly fed to dairy cows on Ontario farms. It is estimated that Ontario dairy farms produce 7 kt of P annually at current levels of P inclusion in the diet. Reducing P levels from the current 0.41% P of dry matter to 0.35% is estimated to save producers CAN $20/cow per year and the environment 1.3 kt/yr without impairing cow health or productivity. Additionally, the reductions might be from inorganic P sources added to the feed, which are more polluting than organic sources because of their water-soluble nature and liability to leaching and runoff.
环境污染的一个主要来源是给奶牛过量投喂磷，这是由于在日粮中添加了“安全边际量”，目的是不影响动物的健康和生产性能。利用在安大略省进行的一项实验对现有的全动物模型进行了评估，以评估其预测磷排泄的适用性。该研究的目的是使用该模型来估计磷排泄水平，以及按照那些报告了日粮中磷充足添加水平的研究建议实施缓解措施的经济和环境影响。均方预测误差和一致性系数分析表明，总体预测接近均值，并且该模型对粪便磷输出量仅有轻微的预测不足。大部分误差是随机的，只有8.9%来自偏离回归线导致的误差，并且该模型没有显示出系统的高估或低估趋势。然后使用该模型通过采用安大略省农场通常投喂奶牛的日粮来预测安大略省的磷排泄情况。据估计，按照目前日粮中的磷添加水平，安大略省的奶牛场每年产生7千吨磷。将磷水平从目前干物质的0.41%降至0.35%，估计每年可为生产者节省每头奶牛20加元，并为环境每年减少1.3千吨磷，同时不会损害奶牛的健康或生产性能。此外，减少的量可能来自添加到饲料中的无机磷源，由于其水溶性以及易于淋溶和径流的特性，无机磷源比有机磷源污染更严重。
