Tuesday, 8 November 2005
139-4

This presentation is part of: Symposium--Environmental Impact of Strategies to Reduce Dietary Phosphorus

Effect of Dietary Phosphorus Content on Amount and Form of Phosphorus Excretion from Dairy Cows.

Richard Kohn and Zhengxia Dou.

One of the most effective ways to reduce phosphorus surplus on dairy farms is to reduce excess phosphorus in diets. In research trials, excessive mineral P supplements fed to dairy cows were well correlated with high amounts of water soluble P in feces (R2=0.95). The findings led to the development of a technique to use fecal P as an indicator of excessive P feeding. The technique was evaluated on commercial dairies in the northeast US. The relationship between dietary P and water soluble P of feces deteriorated (R2=0.46) as compared to the research trials, mainly due to variations in pH and Ca content of feces on the farms. Using a dilute acid to replace water as extractant helped overcome the impact (R2=0.69), and has the potential to serve as an indicator of excessive P feeding. Many dairy farms import most of their grains while producing forages on farm. With typical P feeding levels, this importation results in accumulation of P in farm soils. If dietary P could be reduced by about 33% without impairing production, farm P balance would be greatly improved. Animal nutritionists need to be aware of farm P balance issues to know when to avoid use of byproducts high in P and unnecessary mineral supplements.

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