Limiting the amount of phosphorus fed can reduce the amount of phosphorus in manure, help protect the environment and save you money.

Cows, crops and the environment do not always work in perfect harmony. For example, cows typically produce manure with a nitrogen-to-phosphorus ratio of 1:1, but most crops require these nutrients at a ratio of about 3:1, says Dennis Frame, a county agent in Trempealeau County, Wis., who specializes in nutrient management.

For years, producers applied manure to meet the nitrogen needs of their fields and over-supplemented phosphorus. “Researchers and producers believed that phosphorus was held in the soil and the over-supplementation did not result in runoff,” says Frame.

However, agronomic research now shows that the soil cannot handle the buildup of phosphorus, and the nutrient can make its way to streams and waterways. In response, many producers are choosing to lower the phosphorus level in manure through nutritional strategies. These ration-based methods to limit phosphorus output do not lower milk production or impair reproduction. Instead, they benefit the environment and save money.

Less phosphorus needed
Some producers may have concerns that reducing the phosphorus level in ration will lead to poor reproductive performance — something attributed to low phosphorus feeding in the past. But, producers can safely lower the recommendation of phosphorus fed from 0.5 percent of ration dry matter to 0.4 percent, says Larry Satter, director of the U.S. Dairy Forage Research Center in Madison, Wis.

Satter reviewed 13 feeding trials involving phosphorus and found no difference in reproductive performance — including days open, services per conception, and pregnancy rate — among cows fed phosphorus at 0.32 and 0.4 percent of dry matter when compared to cows fed the nutrient at 0.39 to 0.61 percent of dry matter.

(For more information on Satter’s summary, see “Feed less phosphorus” on page 92 of last September’s Dairy Herd Management.)

Lower supplementation cost
Some nutritionists, such as Bill Steere, a nutritionist with United Feeds in Ionia, Mich., have already started to lower the amount of phosphorus in their clients’ rations by limiting supplementation. After conducting wet chemistry tests on all ingredients, he finds most of his clients’ base rations already provide phosphorus at 0.36 percent to 0.37 percent of dry matter, so very little supplementation is needed to achieve a diet containing phosphorus at 0.45 of ration dry matter.

Steere finds that cutting back on supplements to meet a dietary need of 0.45 percent phosphorus provides an immediate cost savings of approximately 3 cents per cow per day. According to his calculations, lowering phosphorus from 0.5 percent to 0.4 percent dry matter — the eventual goal — would garner a feed bill savings of 6 cents per cow per day. And, since milk production remains the same, income over feed cost also improves.

An example of how this savings occurs in a typical ration is shown in the chart, “Save money by lowering phosphorus supplementation,” above.

Therefore, if a 100-cow producer reduced the phosphorus level from 0.5 percent to 0.4 percent of dry matter in the ration, he would save $6 per day or $2,190 per year.

“Using different feed combinations would vary the savings some,” says Steere. “The most savings I’ve seen so far when lowering the phosphorus level from 0.5 percent to 0.4 percent of dry matter is 8 cents per cow per day.”

And, the reduction in supplementation also lowers the amount of phosphorus contained in the manure. Satter estimates a 100-cow herd producing 20,000 pounds of milk per year and feeding phosphorus at 0.48 percent of the dry matter would generate 1,600 pounds of phosphorus in manure per year. Lowering the phosphorus feeding rate to 0.38 percent would generate 1,200 pounds of phosphorus in the manure — a reduction of 25 percent to 30 percent.

Remove more P in the milk
However, some producers cannot lower phosphorus in manure by reducing supplementation. That’s because they have high-phosphorus forages, and therefore the phosphorus in their base ration already exceeds 0.4 percent of the ration’s dry matter.

“If you’ve got high phosphorus levels in the soil, it carries over into your crops,” says Jeff Opitz, a 650-cow dairy producer in Saukville, Wis. Opitz has not supplemented his cows with phosphorus for eight years, and hasn’t used any commercial fertilizer on his fields for 13 years.

But, Opitz applied another nutritional strategy that reduces phosphorus in manure — he made his cows more feed efficient. By obtaining a higher milk production with the same volume of feed inputs, his cows excrete more phosphorus in milk, thereby reducing the amount of phosphorus in the manure.

In 1995, Opitz’s base ration contained phosphorus at 0.51 percent of the ration’s dry matter. By replacing some high-phosphorus byproducts with lower phosphorus feeds, he was able to reduce his phosphorus level to 0.44 percent. Then, he began improving his feed efficiency. Specifically, Opitz went from feeding 54 pounds of dry matter per cow per day and producing 72 pounds of milk per day in 1995 to feeding 52 pounds of feed per cow per day and producing 82 pounds of milk in 1999. This increased the phosphorus output in the milk by 14 percent.

Opitz calculates that his feed efficiency (pounds of milk/pounds of dry matter) went from 1.48 to 1.64 in the four-year time period. Nutritionists categorize feed efficiency as:

Low Less than 1.4
Medium 1.4 to 1.6
High more than 1.6

Improving feed efficiency requires paying attention to the interaction of feeds in the rumen, especially rumen-degradable protein and carbohydrate sources. The rumen microbes produce the greatest amount of milk when proteins and carbohydrates are available at the same time.

As the chart, “Feed efficiency lowered manure phosphorus values” at right shows, improving the feed efficiency increased Opitz’s ration cost by 9 cents per cow per day. “Feeding for efficiency hits your pocketbook first,” says Opitz. However, over the four-year period, he saw his income over feed cost increase by $1.06 per cow per day, recouping his investment and then some. That extra $1.06 for Opitz’s 650 cows generates an additional income of $386.90 per cow per year, or $251,485 for the herd.

And, the level of phosphorus in the manure of Opitz’s cows declined. His semi-solid manure test shows phosphorus dropping by 9 percent, and the liquid manure test shows a decline in phosphorus of 22 percent.

The time is now

With environmental pressures rising in many states to stop phosphorus runoff, dairy producers need to take the first step in reducing manure phosphorus levels. “We do not know what regulators are going to do,” says Satter. “But if we continue to let phosphorus build up in the soil, the government will force constraints on the dairy industry.”

Talk to your nutritionist or feed representative about implementing these money-making nutritional changes that reduce phosphorus levels in manure.