Phosphorous management begins with feed
By Cindy Snyder, Ag Weekly correspondent
Friday, November 21, 2008 1:58 PM CST
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CINDY SNYDER/Ag Weekly
Michael Musser, a dairy producer from Gooding, left, talks with Charles Stallings, extension dairy specialist from Virginia Tech, during a phosphorus management workshop at Jerome. Stallings is involved with a project in Virginia that is looking for ways to reduce phosphorus levels in manure by reducing phosphorus in dairy cattle diets. |
JEROME, Idaho - “You are what you eat” applies to dairy cows as much as it does to humans.
And that’s opening the door for something Charles Stallings refers to as “precision feeding.” Stallings is an extension dairy specialist from Virginia Tech. He was in Idaho for a series of phosphorus-management workshops held in Preston, Burley, Jerome, and Caldwell. The workshops were sponsored by the United Dairymen of Idaho and the University of Idaho Cooperative Extension Service.
Precision feeding, a takeoff of precision farming, is quite simply matching the ration to the cow’s nutritional needs. But it can also have implications for a dairy’s nutrient-management plan.
For most of his 30-some-year career as a dairy nutritionist, Stallings focused on the nutrients going into the animal. But as dairy production has become more intensive and environmental concerns have become more important, nutritionists are taking a closer look at the nutrients in animal waste. And they’re finding a direct relationship between what’s going in and what’s coming out, especially with phosphorus.
Research shows that every gram of phosphorus fed above a cow’s daily requirement comes out in the feces, Stallings said. But it’s also clear that there isn’t a one-size-fits-all phosphorus requirement. Milk production controls dry-matter intake and the amount of phosphorus required.
Stallings has been working with 187 dairy herds representing over 31,000 cows in the Chesapeake Bay area over the last two years on a voluntary program to reduce phosphorus levels. That’s about one-third of the dairy herd in Virginia.
The participating herds send in a feed sample to be tested for nutrients including phosphorus six times a year and were eligible for an incentive payment if target phosphorus levels in manure were met. For example, farms that were within 5 percent of the target were eligible for a $12 per cow annual payment, while those that were within 15 to 25 percent of the target received $3 per cow. About half of the farms that participated in the first year qualified for a payment.
Stalling was surprised to see that phosphorus levels in the initial rations submitted for the program averaged around 0.42 percent phosphorus on a dry-matter basis.
“That tells me nutritionists had already started reducing phosphorus levels,” he said.
Throughout the first year of the program, phosphorus levels continued to drop every two months when feed was sampled ,reaching a low of around 0.385 percent at the end of the first year. But phosphorus levels began to climb at the start of the second year back to over 0.4 percent.
Stallings thinks economics played a role, and that illustrates just how important ingredient selection in the ration can be. Corn prices skyrocketed in the first half of 2008, which made feeding many byproducts — such as dried distillers grains — relatively inexpensive. While whole corn is considered a relatively low-phosphorus feed ingredient with a phosphorus content of 0.3 percent, DDGs are high at 0.83 percent.
Now that corn prices have fallen, Stallings is looking forward to seeing whether phosphorus levels in the ration come back down as well. But he also recognizes that dairies don’t often select a feed ingredient they’re not already using just to reduce the phosphorus levels in the ration. But for dairies with limited land for applying manure or those with high soil-phosphorus tests, changing ingredients may be one option to help meet their nutrient-management plan.
Stallings estimates that in Virginia, a dairy feeding a ration containing the recommended level of 0.35 percent phosphorus and using a 50-50 alfalfa-corn silage crop rotation would need roughly 1 acre per cow to apply the manure and meet the soil-phosphorus target. Feeding a ration with a 0.45 percent phosphorus boosts the land requirement to approximately 1.5 acres per cow.
Even pastures aren’t as low in phosphorus as some may hope. Mature alfalfa hay has a phosphorus content of 0.28 percent on a dry-matter basis compared with intensively managed pasture at 0.44 percent.
Maturity matters when it comes to forages. Immature grass hay has a phosphorus content of 0.34 percent compared with 0.26 percent for mature grass hay. Corn silage has a phosphorus content of 0.26 percent.
“Certainly, using feed management to reduce phosphorus in diet can influence a waste-management plan,” Stallings said.
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