Animal scientists have long searched for ways to improve what goes into an animal and how the animal uses it.

In the 1990s, what comes out of an animal - waste - is getting increasing attention.

Institute of Agriculture and Natural Resources research shows that carefully formulating the amount of protein in cattle and swine diets can decrease the nitrogen waste released into the environment and sometimes reduce feed costs.

"How we manage our feedlots is going to be a bigger and bigger problem from an environmental standpoint," IANR Beef Nutritionist Terry Klopfenstein said.

Nitrogen is one of the waste products when cattle digest protein. It causes strong odors when released into the air as ammonia and can become nitrate, a potential water pollutant.

IANR researchers studying how efficiently beef cattle, dairy cattle and swine use dietary protein have found that rations often supply too much protein. Animals can perform well on less.

Klopfenstein, who has studied protein use in beef cattle for 30 years, was instrumental in writing the new National Research Council Nutrient Requirements for Beef Cattle, released in April.

The new NRC model classifies protein as rumen degradable and rumen undegradable types.

In cattle's complex digestive systems, rumen microbes digest feed. Rumen degradable protein fuels these microbes. Rumen undegradable protein passes through the rumen and the animal absorbs it for muscle growth. When cattle eat excess protein, both types produce nitrogen waste.

"The main idea about waste management is that if you don't overfeed, the animal doesn't over-excrete," Klopfenstein said.

Klopfenstein used the NRC's computer program to predict feedlot cattle's optimum daily protein needs. Producers can obtain this program, which lets them tailor rations to cattle's needs, from National Academy Press, 2101 Constitution Ave. NW, Lockbox 285, Washington, DC, 20055; World Wide Web: http://www.nap.edu/

"Now we can change the feed protein amount every two weeks, as opposed to 180 days in the past," he said. The more balanced the diet, the less waste nitrogen.

Cattle fed the NRC diet containing 15 percent less protein released 37 percent less nitrogen in urine. This diet costs the same as other diets and produces the same average daily gains and feed-to-gain ratios.

Dairy Scientist Rick Grant formulated a dietary supplement high in rumen undegradable protein that increases milk production and yields better protein response with minimal nitrogen waste.

Lactating dairy cattle eat a high-quality alfalfa diet rich in degradable protein. Grant wanted to use feather meal, an inexpensive source of undegradable protein, to better meet animals' requirements without feeding more protein. But he had to solve one problem.

"Feather meal alone doesn't supply the right balance of amino acids to increase milk protein, but mixing it with blood meal gave a good balance," Grant said.

Feeding lactating cows an 85 percent feather meal/15 percent blood meal mix along with alfalfa rations minimizes total protein fed, maintains milk production and produces higher protein milk for about the same cost as conventional rations.

"We know from previous research that reducing the protein input will mean less nitrogen is excreted, so that's a benefit, too," Grant said.

Swine Scientist Phil Miller found that decreasing crude protein fed to swine from 20 to 16 percent reduced ammonia released from waste by 70 percent.

This diet required mixing synthetic amino acids with feed, an added expense, but one that may become more economically feasible in the future, Miller said.

"Undigested nitrogen is a prime suspect in producing swine containment facility odors, which is becoming a real issue," Miller said. "Manipulating diet in this way is probably going to be important down the road."

The Southeastern Poultry and Egg Association helps fund Grant's research. The Nebraska Pork Producers Association helps fund Miller's research.

-Monica Manton Norby

IANR animal scientists are studying the relationship between diet and waste. Their research shows that carefully formulating the amount of protein in beef, dairy and swine diets can reduce the amount of nitrogen released into the environment through livestock waste.

Beef Nutritionist Terry Klopfenstein's team used runoff ponds at NU's Agricultural Research and Development Center in research to determine what happens to waste excreted by feedlot cattle. This work was part of research on the relationship between dietary protein and waste.