Swine nutritionists at the University of Kentucky (UK) cooperated with UK agricultural engineers to investigate ways of reducing ammonia in stored pig manure. The researchers found ammonia concentration above manure pits was related to dietary protein.

Simulated anaerobic manure pits were constructed containing monitoring instruments to measure production of gases in the pits. Researchers measured ammonia, methane and carbon dioxide in the space above the anaerobic pits over 2- to 3-week periods. Concentrations of volatile fatty acids in the manure were also monitored.

The odorous gases produced by manure are normal end-products produced by anaerobic microorganisms in the manure. A number of volatile gases (some researchers estimate more than 200) are thought to contribute to the odor of swine manure. These gases include ammonia, hydrogen sulfide and other sulfur-containing compounds.

Most of the odorous compounds in manure originate from nitrogen-containing products that have passed through the gut and urinary tract. For example, ammonia results from the decomposition of urea nitrogen in urine and undigested protein in feces. Indole, phenol, para-cresol and skatole are degradation products of the amino acids tryptophan, phenylalanine and tyrosine. Hydrogen sulfide and other sulfide-based odors originate from the breakdown of the sulfur amino acids, methionine and cystine, and from other sulfur compounds.

Results of one of the UK experiments are shown in Figure 1. Finishing pigs in the experiment were fed the following four, corn-soybean meal diets. The first diet was an excess protein diet that had 2% more protein than the amount needed to meet the lysine requirement. The second diet was an adequate protein diet that met the lysine requirement. The third diet was a reduced protein diet that contained 2% less protein than diet 2, but was supplemented with L-lysine. The fourth diet contained very low protein that was 4% below diet 2, but was supplemented with L-lysine, L-tryptophan and L-threonine.

Manure was collected from the pigs and placed in the pits. Note the ammonia concentrations in the air above the manure pits was closely related to the amount of protein in the diet. Ammonia levels in pits containing manure from pigs fed the lowest protein diet were less than half of those of pigs fed the highest protein diet. Volatile fatty acid levels were also altered by the diets. Researchers: Gary Cromwell, Merlin Lindemann, Jim Monegue, Animal Science Dept.; Larry Turner, Richard Gates, Joe Taraba, Biosystems and Agricultural Engineering Dept., University of Kentucky. Phone Cromwell at (606) 257-7534.