By Charmain Tan Courcelle

MISSISSIPPI STATE -- Supplementing poultry diets with activated carbon or other odor absorbers may help take the stink out of chicken manure.

Russell Bazemore, aroma chemist with the Mississippi Agricultural and Forestry Experiment Station, is working on methods to control the odor of poultry manure using absorbers, deodorizers and other chemical compounds. His research may provide relief from unwanted odors for farmers and their neighbors.

"Mississippi and the state's poultry industry continue to grow, and as more people move to areas where poultry is raised, there's increased concern about foul odors," Bazemore said.

His group has examined the odor-reducing ability of three absorbent materials -- chitosan, copper chlorophyllin complex and activated carbon -- when added as poultry diet supplements. Chitosan is produced from chitin that forms the hard shell of crabs and shrimp. It is often used in agriculture as a fertilizer or food preservative, but it also has odor-absorbing traits.

Copper chlorophyllin complex is derived from chlorophyll, which is found in green plants. It can bind to nitrogen-containing compounds such as ammonia. Activated carbon is a highly porous material that can bind to and absorb different compounds.

Smells are a mixture of volatile, or easily evaporated, chemical molecules called odorants. More than 70 odorants contribute to the smell of poultry manure. Odor control strategies are based on capturing these molecules before they get to the nose.

Each industry manages odor differently. For example, livestock facilities treat manure and manure pits with odor absorbers, filter exhaust from enclosed animal operations and trap odors from waste lagoons with manure covers.

"Alternatively, we can try to trap odorous compounds before they exit the animal," Bazemore said.

Bazemore's team raised chicks on a standard poultry diet for their first three weeks. For the next four weeks, the birds received either the standard, control diet or one of five diets that included the standard feed supplemented with various odor absorbent treatments -- chitosan, copper chlorophyllin complex and activated carbon.

The researchers collected manure every week after the treatments were started and analyzed their odor. Odor intensity and unpleasantness were judged by a human "sniff" panel. Manure samples were also analyzed using techniques that allow individual odorants to be identified and scored for importance as odorous components.

The group recorded the live weight of the chickens to determine bird health with and without treatment.

"The treatments did not appear to have a physiological effect on the birds," Bazemore said. "Weight gain was similar for birds fed diets with supplements and those fed standard diets."

Results from the odor analysis showed treatment with copper chlorophyllin complex and chitosan were most effective at lowering the intensity and unpleasantness of poultry manure. However, all of the treatments tested reduced odor to some degree.

"The longer the birds were on the supplemented diets, the better the odors became," Bazemore said.

Further work will be required to determine whether additional odor reduction can be obtained if birds are fed supplemented diets before three weeks of age, Bazemore said.

Because most odor complaints are made after manure is applied to fields as a fertilizer, the scientists evaluated the effect of soil properties on odor.

"We were interested to see whether acidic soils had an effect on manure odor," Bazemore said.

Soils in north central Mississippi are mildly acidic, and results from this study showed that manure odor is more intense and unpleasant on these soils.

"The pH of soil may account, in part, for the overpowering odor of manure after it's initially spread onto a field," Bazemore said. "The degree of odor intensity and unpleasantness can be affected by adjusting the pH."

The smell of ammonia within poultry houses is another common complaint. However, the manure samples collected for this study did not smell strongly of ammonia. Bazemore found the cause of this difference to lie in the pH of the manure -- more alkaline conditions in poultry houses seemed to result in higher ammonia levels.

Bazemore said unwanted odors are not the only reason farmers should be concerned about the pH conditions in their poultry houses. Conditions that favor high ammonia levels are potentially dangerous to the health of humans and chickens.

Released: June 17, 2002
Contact: Dr. Russell Bazemore, (662) 325-3200