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What is your largest phosphorus import?

Randy Pepin, Extension Educator
November 22, 2014

In this series of articles we have been discussing the concept of phosphorus balance on a livestock farm. "What is phosphorus balance again?", you ask. It is the amount of actual phosphorus imported into a farm contained in sources such as feed, fertilizer, animals, and bedding less the phosphorus contained in exported milk, animals, feed, and manure. If the imports of phosphorus remain higher than the exports of phosphorus for a period of time, the usual consequence is an elevated level of soil phosphorus in the fields. Higher than normal soil phosphorus levels result in an increased risk of phosphorus getting into our lakes, rivers, and streams potentially producing blue-green algae blooms.

What is the largest source of imported phosphorus on most dairy farms? On most farms it is purchased or imported feed. What actually is a feed import? A feed import is a feedstuff that comes from a source outside of the system managed as a farm unit on owned or leased land. Almost all dairy farms import proteins and minerals and many also import corn and/or alfalfa and grass hay. A few dairy farms also import other forages such as corn silage and alfalfa haylage. Obviously, farms with fewer imported feedstuffs will have a lower import side of the phosphorus balance sheet.

Are there any options with the proteins and minerals that a dairy farm purchases? One challenge is that many of the commonly fed protein sources for livestock are byproducts. For example, soybean meal and canola meal are byproducts of the vegetable oil industry. Corn distillers, corn gluten meal, and corn gluten feed are byproducts of the starch, corn syrup, or alcohol industries. Most byproducts are a result of extracting a major nutrient for other uses such as oil or starch in the above examples. This leaves the remaining nutrients more concentrated than in the original raw product. For instance, the protein levels in the above byproducts are higher than the protein levels in the original raw products. This process also concentrates the minerals in the byproduct including phosphorus.

Depending on the source, the phosphorus content of corn distillers is similar or slightly higher than that of soybean meal. When corn distillers with a protein content of around 30% is substituted for soybean meal which has a protein content of 47%, nearly twice as much corn distillers as soybean meal must be used to attain the same protein percent in the final mix, depending on the other ingredients in the mix. Higher inclusion of byproduct ingredients usually results in a higher phosphorus content of the mix.

Most nutritionists use ration balancing programs that consider many nutrient and ingredient parameters while simultaneously balancing for least cost formulations; this has served the industry quite well. The use of multiple byproducts with least cost ration balancing has often contributed to ration phosphorus levels above NRC (National Research Council) recommendations. As a result, many livestock farms are feeding phosphorus levels that are above NRC recommendations merely because it is a cheaper ration. It is becoming increasingly rare to add high phosphorus minerals such as mono-calcium phosphate or di-calcium phosphate to livestock rations.

How much would lowering the phosphorus level in a ration increase the cost of the ration? That will of course vary based on many factors such as quality and phosphorus levels of forages, market conditions and availability of commodities, and parameters used by the nutritionist. I have observed that some reduction of phosphorus levels frequently has little or no negative economic consequences. Attaining a phosphorus level right down to the NRC recommended levels may cause the ration cost to increase in some situations.

Is there any herd health or reproduction impact of feeding lower phosphorus levels in a dairy ration? Research has not indicated any additional health benefits of feeding phosphorus above the NRC recommendations. I have personally observed dairy herds with phosphorus levels near the NRC recommended levels with excellent herd health and reproduction.

Research has shown that phosphorus fed in excess of animal requirements ends up in the manure. Therefore, feeding phosphorus closer to NRC recommendations will reduce manure phosphorus levels and decrease phosphorus imports, bringing a dairy farm closer to being in phosphorus balance.

This winter there will be a series of workshops around Minnesota illustrating various strategies for balancing phosphorus imports and exports on livestock farms. Contact your local University of Minnesota Extension Educator later this fall for the time and location of the workshop nearest you or check our website for upcoming events.

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