The key to less odor is using amino acids to balance pig diets.

Odors from pork operations have become one of the major issues in the hog industry. In response, researchers are looking at many ways to reduce odor, including diets.

Recent studies conducted jointly at Purdue University and Pennsylvania State University have focused on the role of diet and hog odors. Since most odors come from the manure excreted by the pig, changing the diet may reduce odor-causing agents in the manure. Diet changes could be a relatively easy and cost-effective way to reduce odors.

Overall, research shows that manipulating crude protein in pig diets will reduce odors. The researchers found manipulating crude protein in pig diets will reduce nitrogen excretion, pH, volatile fatty acids and some other volatile organic compounds in the air.

However, changing the diets came with a cost. Researchers found certain synthetic amino acids increase feed costs $1-2 per pig marketed.

Changing Protein Levels In one research study, typical corn-soybean meal diets fed to grow-finish hogs were compared to protein-deficient and protein-excess diets. The standard diet with 13% crude protein (CP) was compared to a protein deficient diet with 10% CP and the excessive diet with 18% CP. Also compared in the study was a 10% CP diet supplemented with four synthetic amino acids (lysine, methionine, threonine and tryptophan).

Researchers analyzed the fresh manure excreted from the pigs and manure stored in a simulated anaerobic pit. Also analyzed were air samples taken from the headspace. Odor-causing compounds were identified and measured.

The results are shown in Figure 1. Reducing the CP by 3% and adding the amino acids worked the best. This diet reduced nitrogen excretion and ammonium by 28% in the fresh manure and 43% in stored manure compared to the standard diet.

Volatile fatty acids were reduced 50% in the manure from the low CP-amino acid diet compared to the standard diet. Other volatile organic compounds in the air samples were also lower with the low CP-amino acid diet.

Adding Cellulose In another study, researchers added to the 10% CP-amino acid diets either 5% cellulose or 2% oligosaccharide (which was sucrose thermal oligosaccharide caramel in this study, a byproduct of the sugar industry). Pig performance was compared to a standard diet with 13% CP.

Adding the cellulose reduced the pH of fresh manure from 7.8 to 6.4, which also reduces the chances of ammonia emissions into the air. It also reduced ammonium excretion by 68%.

In stored manure, total nitrogen was reduced only 35% as shown in Figure 2, but ammonium nitrogen was reduced 73% (Figure 3).

Adding oligosaccharide to the diet reduced total nitrogen 55% and ammonium nitrogen 62%, compared to the standard diet.

Bacterial fermentation was increased in the colon of the pigs fed the cellulose diet, as shown with increased volatile fatty acid concentrations and lower ammonium nitrogen in fresh manure.

Results from diets with both cellulose and oligosaccharide show volatile fatty acids in stored manure was reduced. Other volatile organic compounds in air samples also were reduced. This results in less odors from the stored manure.

Volatile compounds containing sulfur can create odors in very small quantities. These were cut only 12% with the cellulose added to the diet.

Reducing Sulfur Odors Researchers conducted further study to reduce odors, especially the sulfur-containing odors. They used synthetic amino acids and reduced the use of sulfur-containing minerals like copper sulfate and ferrous sulfate in pig diets.

Standard diets with 13% CP were compared to 8% CP diets supplemented with lysine, threonine, trytophan and methionine to meet required dietary amino acid levels. The researchers substituted copper oxide and ferric chloride for the most of the mineral sulfates.

As in the previous studies, reducing the crude protein and supplementing with essential amino acids reduced ammonium nitrogen in fresh manure 45% and dropped pH levels by one unit. Similar responses were noted in stored manure.

Diets with the low CP-amino acid diets reduced volatile fatty acids by as much as 61%.

Overall, replacing most of the mineral sulfates in the diets across different CP levels reduced volatile sulfur compounds 49%.

Diets with the low CP-amino acids and copper oxide and ferric chloride reduced volatile organic compounds. Plus, the sulfur compounds found in the air samples dropped 63% on this diet compared to the standard diet.

It is apparent that manipulating hog diets can reduce nitrogen excretion, pH, volatile fatty acids and some other volatile organic compounds in the air. Researchers found some solutions by changing the crude protein, especially by balancing the available amino acids, and the changing the carbohydrate components with fiber ingredients.

These measures can help. Reducing the nitrogen excretion means almost 50% less land needed for manure application. Reducing the volatile organic compounds means less odorous compounds for entering the air.

The diet changes came at a cost of $1-2/pig marketed.

Contributing researchers from Purdue University: Alan Sutton, John Patterson, O. Layi Adeola, Brian Richert and Dan Kelly, Animal Sciences; Albert Hebe r and Don Jones, Agricultural and Biological Engineering.

Contributing researchers from Pennsylvania State University: Ken Kephart, Dairy and Animal Sciences, and Ralph Mumma and Ed Bogus, Entomology. This research was partially funded by the National Pork Producers Council.

University of Minnesota researchers are investigating whether manipulating pig diets can reduce hydrogen sulfide emissions.

Pigs are involved in feeding trials right now for these experiments.

The researchers are feeding a low sulfur diet instead of a typical starter diet sequence.

"We are trying to measure the effects of those diets on hydrogen sulfide gas, as well as on general overall odor," says Jerry Shurson, extension swine specialist, University of Minnesota.

"We think by paying attention to the sulfur content of ingredients, we can deliver the same amount of nutrition to support optimum performance while still minimizing sulfur excretion," Shurson explains. "This may have some influence on odor and hydrogen sulfide levels in confinement buildings."

Results of these experiments will be available in mid-to-late 1998.