A small change in your milking ration could help protect the environment — and save you some money, too.

Most dairy producers are feeding more phosphorus (P) than their cows need, says Larry Satter, a researcher at the U.S. Dairy Forage Research Center, Madison, WI. The excess P ends up in the manure and becomes a threat to streams and lakes.

“Phosphorus is a major environmental threat,” says Satter. “It's what causes algae to grow on our lakes, and agriculture is a major contributor.”

He says P is overfed because of a “deeply imbedded notion” that the nutrient improves reproductive performance. The belief stems from decades-old research in other countries and with rations much lower in P than those fed in the U.S. today.

Also, until the last few years, no research was done on the minimum amount of P needed in dairy cow diets.

“So not knowing where the basement floor was, people were inclined to exaggerate the margin of safety,” says Satter. “That encouraged excessive feeding.”

Another part of the problem: “There's been aggressive marketing of phosphorus supplements,” he says. “It's a profit item for people in the feed industry.”

Recent surveys reveal that dairy producers are feeding an average of 0.48% dietary P. Satter recommends formulating rations with 0.35-0.4% P.

“Depending on the diet ingredients, that may or may not require a little bit of phosphorus supplement,” he says. “In many, many cases, it won't.”

His recommendation is in line with new National Research Council (NRC) guidelines published early this year. Even cows producing 30,000 lbs of milk per year don't need more than 0.38-0.4% P, he says.

Feeding more than recommended levels won't improve reproduction or put more milk in the tank. But it will add to the P load of manure spread on fields. And much of the P in high-phosphorus manure is water soluble, so it's susceptible to runoff.

If you don't know the P level of your total ration, ask your nutritionist or veterinarian. If you're feeding more than is needed, make the necessary adjustments.

The changes will probably take place in the concentrate portion of the ration, not the forages. Although alfalfa is fairly high in phosphorus, soybean meal has twice as much, and some byproduct feeds have even more.

“As a general rule, concentrates have more phosphorus than do forages,” says Satter. “Alfalfa has more phosphorus than does corn silage, and protein supplements have the most of all.”

Since graziers typically use hefty supplement programs, they're not off the hook. If cows are grazing paddocks that are permanently in grass, they're probably depositing more phosphorus in the manure than the grasses can utilize.

“A lot of these folks are going to have a gradual buildup of phosphorus in the paddocks.”

He figures cutting back to recommended P levels could save dairy producers $100 million annually, and might head off tougher manure disposal regulations. Among the numerous environmental challenges facing agriculture, this one is relatively easy to deal with, he says.

“Some of the steps to meet environmental regulations will cost money,” says Satter. “This is one step, however, that saves the dairyman money. So we shouldn't delay with these opportunities.”