Use of Soybean Hulls to Mitigate Swine Lagoon Odors

One of the greatest problems facing pig producers today is manure and lagoon management. There is a constant pressure to produce an excellent product and to keep the consumer satisfied with the environment. Large-scale swine production units give off an unpleasant odor, which upsets many neighbors. In addition, carbon dioxide, hydrogen sulfide, and ammonia are found in manure on the feedlot floor. These chemicals, in high concentrations, can be deadly to pigs or feedlot employees. High levels of carbon dioxide cause the pH of the surface manure to rise, which in turn causes the levels of ammonia to rise. The accelerated ammonia release has an adverse affect on the pH and the concentrations of both chemicals rise until they reach equilibrium. Also, the excess nitrogen seeps into the ground from the manure and causes a variety of environmental problems.

However, new studies are showing that the addition of a dietary fiber source, such as soybean hulls, can significantly increase the retention of nitrogen in manure, resulting in less being volatized into the air. One study done with grow-finish pigs (DeCamp et al., 2001) showed that 10% soybean hulls added to the diet decreased the manure pH, and the ammonia. From a performance perspective, there was one adverse effect on the pigs' carcass merit: a greater adjusted backfat at the end of the trial, from 14.7 mm to 15.8 mm. A second study with growing barrows found similar results, using soybean hulls, coconut expeller, and dried sugar beet pulp (Canh et al., 1998). The study found that the soybean hulls were the greatest reducer of pH and ammonia. The addition of such nonstarch polysaccharides (NSP) increases the volatile fatty acid concentration, which in turn reduces the pH and ammonia release. In a similar study with finishing pigs, soybean hulls were most effective at reducing the ratio of fecal and urinary nitrogen. This reduction in ratio is what causes the ammonia levels to decrease (Mroz et al., 2000).

Although the results from these studies are promising from the standpoint of nitrogen reduction, there are still many unanswered questions. High fiber diets typically yield less energy to grow-finish hogs than traditional diets, and can interfere in the use by the pigs of other nutrients like protein, vitamins, and minerals. In addition, bacterial breakdown of fiber may result in a different objectionable odor than that of ammonia. More work needs to be done in this area before recommendations are made to producers.

By Amy Keys and C. M. Wood, Animal & Poultry Sciences, VA Tech

Literature Cited

Canh, T. T., A. L. Sutton, A. J. Aarnink, M. W. Verstegen, J. W. Schrama, and G. C. Bakker. 1998. Dietary carbohydrates alter the fecal composition and pH and the ammonia emission from the slurry of growing pigs. J. Anim. Sci. 76:1887-1895.

DeCamp, S. A., B. E. Hill, S. L. Hankins, D. C. Kendall, B. T. Richert, A. L. Sutton, D. T. Kelly, M. L. Cobb, D. W. Bundy, and W. J. Powers. 2001. Effects of soybean hulls in a commercial diet on pig performance, manure composition, and selected air quality parameters in swine facilities. J. Anim. Sci. 79(Suppl.1):1039.

Mroz, Z., A. J. Moeser, K. Vreman, J. T. van Diepen, T. van Kempen, T. T. Canh, and A. W. Jongblied. 2000. Effects of dietary carbohydrates and buffering capacity on nutrient digestibility and manure characteristics in finishing pigs. J. Anim. Sci. 78:3096-3106.

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Use of Soybean Hulls to Mitigate Swine Lagoon Odors