Researchers at the University of Illinois evaluated the impact of different levels of crude protein (CP) on fecal odor in growing pigs. They found that fecal odor can be reduced by feeding reduced CP diets

Five typical corn-soybean meal diets were fed to five, 80-lb. barrows. The diets contained 12, 14, 16, 18 and 20% CP, which was adjusted by increasing or decreasing the levels of corn and soybean meal in the diets. Crystalline amino acids were included in order to maintain the ideal protein pattern.

The pigs were housed in metabolism crates in a Latin square design, which allows each pig to consume all of the diets throughout the experiment. Pigs were allowed four days to adapt to each diet and then total feces were collected for five days. Upon collection, feces were frozen until odor analysis.

The feces were thawed and mixed and then analyzed by a trained human odor panel. The 10-member panel consisted of non-smoking, non-pregnant women between the ages of 30 and 55 who were not taking medications.

The panel evaluated the following odor characteristics: manure/fecal, urine/ammonia, musty/wet hay, overall odor intensity, tolerability (for a 24-hour period) and offensiveness. A 15-point scale was used, with increased scored indicating fecal odor was worsening.

When the CP level increased from 12% to 16%, fecal odor scores increased for offensiveness, tolerability and overall intensity. However, when CP levels increased from 16% to 20%, odor scores for offensiveness, tolerability and overall intensity were similar to those from 12% and 14% CP diets.

Researchers: Jennifer Wubben, David M. Albin, Michelle Smiricky and Vince Gabert, University of Illinois. Phone Gabert at (217) 244-2870 or e-mail him at