Phosphorus content of feeds

The National Research Council’s 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.

NRC P,
% DM

CVAS P,
% DM

Forages
Alfalfa hay, immature	.31	.34
Alfalfa hay, mature	.28
Grass hay, immature	.34	.27
Grass hay, mature	.26
Barley silage	.30	.36
Corn silage	.26	.23
Rye silage	.42	.42
Pasture, intensively managed	.44
Grains
Barley	.39
Corn	.30	.28
Protein Meals
Cottonseed meal	1.15	1.08
Peanut meal	.64
Soybean meal	.70	.69
Fish meal	3.05	2.68
Whole Seeds
Cottonseeds	.60	.63
Soybeans	.60	.58
By-Products
Brewers grains, dry	.67
Brewers grains, wet	.59	.61
Corn gluten feed	1.00	1.05
Distillers grains	.83	.74
Hominy	.65	.50
Wheat bran	1.18
Low P Feeds
Bread waste	.20	.25
Citrus pulp	.12	.12
Cottonseed hulls	.12	.14
Molasses, sugarcane	.10
Soybean hulls	.17	.15
Sugar beet pulp	.09

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.

By Charles C. Stallings, Extension Dairy Scientist, Nutrition and Forage Quality
Dairy Pipeline newsletter - Virginia Cooperative Extension

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Phosphorus content of feeds