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Overfeeding Phosphorus Wastes Money, May Complicate Manure Management

Overfeeding phosphorus costs dairy farmers about $12 to $15 per cow per year in added feed costs, according to Larry Satter, a dairy scientist with the U.S. Dairy Forage Research Center at UW-Madison.

Satter surveyed consultants, feed industry reps and state extension specialists across the nation last year, and found that on average, diets for milking cows contained about .48 percent phosphorus. The National Research Council recommends about .38 percent for typical milking cows (varying slightly according to production levels).

Many producers feed high phosphorus levels in hopes of improving reproductive performance. That”s a barnyard myth, at least for dairy cows. At very low phosphorus levels, .15 percent to .2 percent, reproduction can suffer. Beef cows might encounter these levels grazing corn stalks or winter pasture, for example. “But dairy cows aren”t ever going to hit these low levels on any dairy diet we could put together,” Satter says.

Reducing the amount of supplemental phosphorus to NRC-recommended levels will save money and also reduce the phosphorus in manure by 25 percent to 30 percent. “When and if we face regulations on manure applications based on phosphorus content, this would reduce the amount of land needed for manure applications,” Satter says. Current regulations in Wisconsin are based on nitrogen levels, and apply to herds of 700 cows or more. But this could change; regulators could reduce the minimum herd size and base land requirements on the amount of phosphorus that could be taken up by crops.