Dairy Cattle Phosphorus Requirements Revisited

Dr. Ronald L. Boman

USU Extension Dairy Nutritionist

At the 2nd annual "Intermountain Nutrition Conference" in Salt Lake City during January, Dr. Larry Satter presented evidence that we are over-feeding PHOSPHORUS in beef and dairy cattle rations. Dr. Satter is a world renowned dairy research nutritionist working at the U.S. Dairy Forage Research Center and the University of Wisconsin. He explained that "NRC recommendations for phosphorus are in fact adequate to excessive. Many dairy producers are feeding phosphorus in excess of these recommendations."

One problem is that the availability of phosphorus in feeds and in phosphorus supplements was underestimated when the recommended levels were published by NRC in 1989. New scientific evidence in the U.S. and Europe indicates that these availabilities are higher than earlier estimated. Also, low phosphorus levels were thought to be linked to low reproductive performance and reduced milk production.

Research was conducted at Utah State University some 20 years ago by Drs. Call and Butcher with dairy cows fed diets containing phosphorus at either 65, 85 or 100% of NRC. There was no statistical difference in milk production or in reproduction due to any of these levels of phosphorus. Dr. Satter summarized several research trials with lactating dairy cows fed a low (.32% of DM) or high phosphorus (.39% of DM) ration. There were 390 cows in each of these groups. There were no differences in reproductive parameters of these two groups. In six trials (125 cows/group) milk production was similar on diets with low phosphorus (.30-39% of DM) compared to high phosphorus (.39-65% of DM).

A very real problem with feeding excess phosphorus (besides the extra cost involved) is that dairy producers now are having to account for this nutrient in their waste management programs. Environmental concerns regarding phosphorus are associated with pollution of streams and lakes. Excess phosphorus in water causes algae and aquatic plants to grow very rapidly. Decomposition of the algae and aquatic plants consumes the oxygen in the water and adversely affects the fish and other aquatic animal life. Excess phosphorus in the diet means more phosphorus in the manure, which limits the amount of manure that can be applied to crop land. Also with current low milk prices, it seems only reasonable to try to reduce the phosphorus in dairy rations, since neither milk production nor reproductive efficiency are improved by exceeding NRC recommendations. THE ONLY EXCEPTION TO LOWERING PHOSPHORUS is in the first 45 to 60 days after calving when dry matter intake is low. During this period 0.65% phosphorus (DM basis) is acceptable. If I can be of further assistance, please feel free to contact me at (435) 797-2163 or ronb@ext.usu.edu.

References

Knowlton, Katherine F., and Rick Kohn. 1999. "We've got to stop overfeeding phosphorus." Hoard's Dairyman. June, page 437.

Satter, L.D., and Z. Wu. 2000. "Phosphorus-Nutritional Management of Phosphorus in Dairy and Beef Rations. Proceedings, 2nd Annual Intermountain Nutrition Conference; Salt Lake City, Utah.

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