Hog odors can be reduced by feeding highly digestible, low-fiber ingredients, reducing the protein content and adjusting the macro minerals of the diet, according to researchers at North Carolina State University (NCSU).

NCSU researcher Theo van Kempen is studying the acidification of pig urine through the addition of phosphoric acid to the diet instead of dicalcium phosphate . Van Kempen says the acidification works well for reducing ammonia emissions and methane production.

The phosphoric acid and gypsum replaced dicalcium phosphate and limestone as sources of phosphorus and calcium in the study. Ammonia emissions were reduced from 20% to 50% and methane was also reduced.

Preliminary data from the study suggests odor emissions actually increased with the phosphoric acid treatment.

The North Carolina research conflicts with earlier Dutch research findings that the phosphoric acid reduces hog odors.

Researchers are also studying ways to remove ammonia from the environment and ways to convert it into non-odorous compounds.

High ammonia levels in barns are irritating for pigs and humans. In people, the irritation can result in lung damage, greater susceptibility to opportunistic infections, loss of productivity through increased sick leave and even disability. In hogs, the effects are similar, but appear as "failure to thrive" and result in low market weights and reduced profitability.

The NCSU research focused on engineering microorganisms to be more efficient in removing ammonia from their environment and converting it into stable, non-odorous compounds. The microorganisms can be engineered to efficiently utilize ammonia. Used as a probiotic or in bio-filters, they may help to reduce ammonia levels.

The researchers also tested feed ingredients as a contributor to hog smell. Most odor compounds are derived from remnants of the digestive process and end up fermenting in the large intestines or in the manure.

The fermentation of protein results in odorous compounds such as para-cresol and phenol, which have the highest correlation to odor sensation. The key to reducing odor production is reduce the remnants of the digestive process, particularly protein, and the undigested secretions made by the animal.

Both can be reduced, according to the researchers, by choosing highly and easily digestible feed ingredients. Fibrous ingredients are not only poorly digestible, but they also increase the protein secretions by the intestines.

In highly fibrous diets, fiber-degrading enzymes may reduce the impact of the fiber on odor production. The NCSU researchers admit that research in this area is scant, but point to a 2-3% improvement in protein digestibility. That change can reduce the indigestible protein by 13% to 20% and has a positive impact on odor emission.

Researchers: Theo van Kempen and Jeanne Koger, North Carolina State University. Phone van Kempen at (919) 515-4016 or e-mail t_vankempen@ncsu. edu.