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Virginia Cooperative Extension - Knowledge for the CommonWealth

Phosphorus content of feeds

Dairy Pipeline: July 2006

Charles C. Stallings
Extension Dairy Scientist, Nutrition and Forage Quality
(540) 231-3066, email:

The National Research Councilís 2001 recommendations for phosphorus in rations in most Virginia herds would be .32 to .38% of the dry matter. Since forages are typically lower in phosphorus than protein meals and certain by-product feeds (cottonseeds, wheat bran and midds, brewers grains, distillers grains) it is possible to sometimes reduce phosphorus by feeding more forage. For this to occur the forage must be of good to excellent quality. See the following table for P concentrations in forages from the 2001 NRC as well as Virginia summaries from Cumberland Valley Analytical Services (CVAS) for 2005.
Alfalfa hay, immature
Alfalfa hay, mature
Grass hay, immature
Grass hay, mature
Barley silage
Corn silage
Rye silage
Pasture, intensively managed
Protein Meals
Cottonseed meal
Peanut meal
Soybean meal
Fish meal
Whole Seeds
Brewers grains, dry
Brewers grains, wet
Corn gluten feed
Distillers grains
Wheat bran
Low P Feeds
Bread waste
Citrus pulp
Cottonseed hulls
Molasses, sugarcane
Soybean hulls
Sugar beet pulp

There are some slight differences but most values are similar. Phosphorus content of forages does vary with maturity. More mature legumes and grasses tend to have less phosphorus. Also, rye silage and intensively managed pastures have higher P concentrations than corn or barley silages. However, overall, forages do have lower concentrations of phosphorus than many other feeds used in dairy rations. When we bring feeds into the ration to supply protein many times we also bring phosphorus. This is especially true for the protein meals, whole seeds, and by-product feeds; while grains such as barley and corn have less.

The question arises as to what can be done when the phosphorus content of the ration is excessive and no inorganic sources are included in the ration. I have identified some feeds that are low in phosphorus (.20% P or less). Some of these—such as citrus pulp, cottonseed hulls, and soybean hulls—are readily available. Others may have application under certain circumstances and limitations. In conclusion, to manage phosphorus content of rations it is necessary to analyze phosphorus levels and in some cases look for alternative feeds.


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