UNIVERSITY PARK, Pa. -- For years, dairy producers have added phosphorus to the diets fed to cows to improve their health, but now environmental concerns associated with overfeeding the mineral to production animals have spurred research into the practice.

Zhiguo Wu, assistant professor of ruminant nutrition in Penn State's College of Agricultural Sciences, has teamed with groups from the University of Pennsylvania, Cornell, Virginia Tech, University of Maryland and University of Delaware to study dairy herds across the Mid-Atlantic Region.

The phosphorus study, headed by Zhengxia Dou at the University of Pennsylvania, is sampling dairy herds in Pennsylvania, Virginia, New York, Maryland and Delaware.

"Farmers have known for decades that phosphorus is an essential mineral required by both plants and animals for processes such as cell division, protein synthesis and energy metabolism," says Travis Edwards, a research technician working with Wu on the study. "But studies have shown that as the level of phosphorus in the diet is increased above the animal's requirement, the amount of phosphorus in the manure increases as well."

What the animals do not utilize is passed through to be excreted in manure. The manure then is applied to farmland, adding to the phosphorus level of the soil. If the crops grown on that land do not use the mineral, the level continues to build. Eventually, phosphorus can leach into ground and surface water.

"The increased nutrient level of the water promotes an increase in algal growth. As these algae die, bacterial decomposition takes place," Edwards explains. "This decomposition uses oxygen in the water, leaving less for fish. In particularly heavy concentration, this can cause areas of fish kill. This process is known as eutrophication and is seen everywhere from farm ponds to the Chesapeake Bay." According to Edwards, recent studies have indicated that the level of phosphorus in dairy cow rations can be reduced to .35-.38 percent of the total ration. "The state average is about .45 percent, but is decreasing at a rapid rate thanks to the cooperation of feed industry and independent nutritionists," says Edwards. "However, the demonstrated sufficient level has not yet been accepted by everyone. Some think that elevated levels of phosphorus in the ration may help improve the breeding performance of dairy cows, and others feel that the requirements are underestimated in general."

Studies on the effect of phosphorus on breeding and milk production -- which led to the conclusion that more was better -- were conducted from the 1920s through the 1950s. But, Edwards points out, at that time animals were being fed diets low in phosphorus, energy and protein due to poor forage and pasture sources.

"Dairy cows in today's industry are fed much higher-quality feeds to maintain increased levels of milk production," says Edwards. "Therefore, reviewing the studies today reveals that the response they saw with phosphorus supplementation probably was due to the basal level of phosphorus being very low, while low energy and protein content exacerbated the situation and had adverse effects on milk production and breeding performance."

More recent studies showed no benefit to increased phosphorus levels, but Edwards points out that those results were obtained using smaller numbers of animals. He notes that the current study is designed to overcome this issue by sampling private herds across the region, involving thousands of animals.

Penn State is studying 27 herds to determine what effects phosphorus level may have on milk production and reproductive performance. The study is to be conducted over a three-year period, with the first year finished this June. Four times per year, feed and manure samples are taken from each farm involved in the study. Samples are analyzed for their phosphorus content.

"By analyzing the feed and manure, we can gain an estimate of phosphorus utilization -- in other words, the phosphorus going in versus the phosphorus coming out," says Edwards. "Monthly reports on each herd's milk production and reproductive performance are tracked and compiled."

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EDITORS: Contact Travis Edwards at 814-863-4204 or tedwards@das.psu.edu.

Contact:

Jeff Mulhollem jjm29@psu.edu 814-863-2719 814-863-9877 fax #151