Many Feed Cattle More Phosphorus Than Needed

5/18/2013 7:00 AM
By Teresa McMinn Southeastern Pa. Correspondent

LANCASTER, Pa. — Jamie Jarrett said she gets excited when folks talk phosphorus.

Jarrett a native of Bakersfield, Calif., has a doctorate in dairy cattle nutrition from Virginia Tech. Her research included ways to improve estimations of phosphorus bioavailability in lactating dairy cows.

Today, Jarrett is a dairy marketing nutritionist for Purina Animal Nutrition.

Recently, she was at a feed management conference at the Lancaster County Extension office to explain ways phosphorus can be applied to feed management. Roughly 50 folks were at the event.

“There’s phosphorus in different forms,” Jarrett said as she discussed the implications of the chemical element leaching into the Chesapeake Bay watershed.

A 2001 recommendation by the National Research Council indicates that a cow’s diet should contain between roughly 0.32 and 0.42 percent phosphorus.

“We still see producers feeding much beyond this requirement,” Jarrett said.

That might be because farmers are worried that a change in their feeding habits could result in a negative effect on milk production or reproductive performance, according to her presentation.

Jarrett discussed a chart that showed, in theory, how phytate should be completely hydrolyzed in the cow’s rumen.

“There are limitations to this model,” she said, adding that the majority of phosphorus is absorbed in a cow’s small intestine.

She also said phosphorus is recycled in the animal’s saliva.

“That animal does a great job of recycling phosphorus and you can see that,” she said.

Jarrett said her research at Purina included several studies of cows on various diets.

“We had a positive control,” she said, adding that the studies collected samples of urine, serum and milk.

The goal of the study focused on digestion and absorption in the large and small intestines.

A reduction in phosphorus in the cow’s diet does not create a negative impact on reproductive performance, she said.

“We’re looking to make our animals better,” she said of efforts to fine-tune the nutrients in feed. “I think people are starting to catch on.”

Denise Coleman, state conservationist for the Natural Resources Conservation Service, said nitrogen and phosphorus feed algal blooms that block sunlight to underwater grasses and suck up life supporting oxygen when they die and decompose.

“These resulting dead zones of low or no oxygen can stress and even kill fish and shellfish,” she said via email. “Algal blooms can also trigger spikes in pH levels, stressing fish, and create conditions that spur the growth of parasites.”

Coleman said NRCS in Pennsylvania focuses on issues such as proper nutrient management, erosion reduction and other measures producers can take when spreading manure on their crop fields.

Dan Ludwig, southeast Pennsylvania grazing specialist and Pennsylvania feed management specialist for the NRCS, said it’s important for dairy farmers to know the correct phosphorus balance animals need for growth, production and reproduction.

“Their rations should be balanced to avoid oversupplementation,” he said via email.

Excess nutrients that are not used by animals are excreted in the manure.

“When that manure is spread as fertilizer, any excess phosphorus that is not taken up and utilized by the crop remains in the soil,” Ludwig said.

That can lead to phosphorus accumulation in the soil over time, which could limit the amount of manure a producer can spread on fields, he said.

“Feed rations are balanced to provide the nutrient needs of the animals, but the costs of the feed ingredients used does play a role,” he said. “In many instances, byproduct feeds are used as a method to provide the nutrient needs of the animals and control the feed costs.”

Those byproduct feeds are typically higher in phosphorus than the whole grain from which they were derived, he said.

“Since the combination of forages and grain mixes used to create rations typically can provide the phosphorus needs of the animals, additional inorganic phosphorus may not need to be added to the rations,” he said.

“This in itself can make an impact on the price a producer pays to create their rations.”

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