Purdue University 1996 Swine Day Report

Swine Diets to Reduce Ammonia and Odor Emissions

A. Sutton, J. Patterson, D. Kelly, D. Jones, and A. Heber
Departments of Animal Sciences and Agricultural and Biological Engineering, Purdue University

K. Kephart, R. Mumma, and E. Bogus
Departments of Animal Science and Entomology, Pennsylvania State University

The threat of odors from pork production operations in some areas of the country has restricted growth of the industry and has created negative relations between neighbors. Odors from manure result from microbial decomposition. Reducing nutrient excretions and controlling compounds creating the odors in manure are needed to significantly reduce odors from pork production. Minimizing nutrient excesses in diets, improving nutrient digestibility and utilization, and balancing nutrient levels to meet the needs of the pig and the microflora in the digestive system are approaches needing evaluation as potential methods of odor control. Reducing the dietary crude protein level and supplementing with synthetic amino acids have reduced nitrogen excretion from pigs, with a 25 to 30% reduction reported and a 40 to 50% reduction theoretically possible. Changing the carbohydrate structure in the diet to increase bacterial utilization of nitrogen in the cecum and colon results in a significant reduction of nitrogen excretion in urine. The objectives of this study were to determine the sources and concentrations of odorous compounds in cecal contents, fresh manure and anaerobically stored manure from swine, and to determine the effects of dietary nitrogen manipulation on production of odorous compounds.

Materials and Methods

Three groups of four crossbred gilts (12 total), averaging 100 lbs., were surgically cannulated in the cecum. The pigs were fed each of four diets in 4 X 4 replicated Latin Square designed experiments with three replicate trials. Dietary treatments (Table 1) included (1) 10% crude protein (protein deficient diet); (2) 10% crude protein with four synthetic essential amino acids (lysine, threonine, tryptophan and methionine; amino acid supplemented diet); (3) 13% crude protein (standard commercial diet); and (4) 18% crude protein (protein excess diet). All diets were corn-soy base fortified with a vitamin and mineral premix and tylan. After a 2 week adaptation to each diet and placement in digestibility crates, cecal samples were collected on three separate days, four hours after feeding. Manure and urine samples were collected over a 24-hr period on three separate days. The manure and urine were mixed and initial manure samples were obtained; subsamples were used for 90-day anaerobic incubations. During the incubations, fresh manure was added three times per week. Separate gas samples were collected from the daily cecal and fresh manure samples on thermal desorption tubes, sealed, stored frozen and shipped to the Pennsylvania State University Pesticide Research Laboratory for analysis of organic compounds using gas chromatography and mass spectrometry procedures. Gas samples were collected from anaerobic incubation flasks each week from 60 to 90 days after initiation of the study using the same techniques. Liquid matrix subsamples were analyzed for short chained volatile fatty acids with gas chromatography methods. Ammonia and total nitrogen was assayed using micro-Kjeldahl techniques.

Results and Discussion

The different levels of dietary nitrogen significantly affected nitrogenous compounds and volatile fatty acid concentrations in fresh manure and manure stored in anaerobic incubations. Other odorous compounds in the head space from cecal, fresh manure and anaerobic manure varied in composition and concentrations between dietary treatments.

The pH and ammonia nitrogen concentrations in cecal contents were not affected by dietary treatments (Table 2). However, total nitrogen concentrations in cecal contents were lower (P<.05) in pigs fed the deficient protein diet and the amino acid supplemented diet, as compared to the standard and excess protein diets. From 17% to 20% less nitrogen was present in the cecal contents of the amino acid supplemented diet compared to the higher protein diets. The dry matter content of cecal contents from pigs fed the standard and excess protein diets was lower (P<.05) than the other diets. Propionic and valeric acids were higher in cecal contents of pigs fed the standard diet compared to the other diets, except for propionic concentrations being similar in the amino acid supplemented diet (P<.05). On a molar % basis, the lowest proportion of butyric acid in the total VFA concentrations was observed with the amino acid supplemented diet. The propionic acid concentrations and molar percentage proportion of the total VFA in cecal contents of pigs fed the excess protein was numerically lower than the other diets. Higher propionate levels in cecal contents favor more efficient energy utilization for the pig. Lower butyric acid concentrations in cecal contents of pigs fed the amino acid supplemented diet resulted from either reduction of microbial populations metabolizing butyric acid, or reduced levels of protein degradation of existent bacterial populations. Since ammonia concentrations were not changed by diet and total nitrogen was lower in the cecal contents, it appears that reduced protein degradation resulted.

The amino acid supplemented diet significantly reduced (P<.05) pH, ammonia nitrogen, and total nitrogen in fresh manure compared to the other dietary treatments (Table 3). Dry matter level was higher in fresh manure from pigs fed the amino acid supplemented diet, and dry matter was decreased with increasing levels of dietary crude protein (P<.05). Ammonia nitrogen levels were reduced 25%, 28% and 40% (P<.05) in fresh manure on a dry matter basis when comparing the amino acid supplemented diet with the deficient protein, standard and excess protein diets, respectively. Total nitrogen was reduced 20%, 28% and 42% (P<.05) in fresh manure on a dry matter basis when comparing the amino acid supplemented diet with the deficient protein, standard and excess protein diets, respectively. The only change in volatile fatty acid concentrations were reduced propionic, butyric and valeric acid concentrations in fresh manure from pigs fed the excess protein diet (P<.05). On a molar percentage basis, there was a higher proportion of propionic acid with the amino acid supplemented diet compared to the other diets, suggesting a change in the microbial fermentation process in the colon. Butyric and propionic acid levels were lower in manure from the excess protein diet, probably due to excess ammonia or the elevated pH level (8.13) of the manure suppressing microbial metabolism. Reduced levels of ammonia and total nitrogen in fresh manure compared to cecal contents suggested that much of the ammonia and total nitrogen reaching the colon was used for further bacterial growth and less absorbed for excretion in urine. Similarly, less volatile fatty acids were excreted in fresh manure and proportionally more efficiently used by the pig and/or the intestinal bacteria.

Similar responses to the dietary treatments were evident during the anaerobic incubation of the manures (Table 4). The pH of manure from pigs fed the amino acid supplemented diet was lower (P<.05) than the other dietary treatments. Ammonia and total nitrogen concentrations were significantly lower in stored manure from pigs fed the amino acid supplemented diet, followed by incremental increases of nitrogen compounds in manure from the deficient protein diet, standard protein diet and excess protein diet, respectively. Ammonia nitrogen concentrations on a wet basis were reduced by 32%, 43% and 56% from pigs fed the amino acid supplemented diet compared to the deficient, standard and excess protein diets, respectively, when incubated anaerobically (P<.05). Similarly, total nitrogen levels in the manure were reduced by 29%, 43% and 55% when comparing the amino acid supplemented diet with the deficient protein, standard and excess protein diets, respectively (P<.05).

Total volatile fatty acid concentrations were highest with the standard diet with a very high proportion of acetic acid. Conversely, volatile fatty acids were reduced with the deficient and excess protein diets. This response reflects a similar trend in the fresh manure from pigs fed the excess protein, but is not similar to VFA production in the manure from pigs fed the deficient protein diet. Therefore, it appears that there was insufficient nitrogen in the deficient diet to promote microbial decomposition in the anaerobically stored manure. Also, there was an imbalance in the C:N ratio or insufficient carbohydrate in the excess protein diet to promote enhanced microbial decomposition. Although the reduced pH in the amino acid supplemented diet was not solely due to increased VFA, the lower pH and less ammonia and total nitrogen excretion suppressed ammonia volatilization from stored manure. Also, reduced microbial metabolism and growth was evident by lowered VFA production in manure from the amino acid supplemented diet compared to the standard diet.

Bifidobacteria, lactobacilli and total anaerobic bacterial concentrations in cecal contents are summarized in Table 5. There was no apparent dietary effect on the microbes analyzed, except for a trend towards increased populations of total anaerobic bacteria in cecal contents of pigs fed increasing levels of dietary protein. Additional study is needed to identify specific groups of microorganisms and their end products which may be important in cecal metabolism.

Mass spectrophotometry analysis of gas collected from cecal content has identified ethanol, propanol, butanol, n-propyl acetate, dimethyl disulfide, dimethyl sulfide, s-methyl propanethionate, 2-butanone, and the ethyl esters of propanioc acid and butanoic acid. Similar compounds were identified in gas collected from fresh manure at relatively lower concentrations, but with ethanol, propanol, dimethyl disulfide and 2-butanone as the primary organic compounds. Prevalent concentrations of ethanol, propanol, dimethyl sulfide, dimethyl disulfide, and carbon disulfide were observed in gas collected from anaerobically stored manures. Further studies need to be conducted to discern specific metabolic microbial pathways creating these compounds and develop means to reduce specific sulfide compounds causing odors.

Conclusions

Based upon this study, reducing the crude protein level of pig diets and supplementing with essential amino acids to meet the pig's lean tissue production requirement, significantly reduced total nitrogen excretion and ammonia concentrations, and altered the concentrations and ratios of selected volatile fatty acid concentrations and other odorous compounds identified in fresh manure. Similar more pronounced results were observed with anaerobically stored manures. Current standard diets often meet the nutritional needs of the pig for the most limiting amino acids, but exceed other amino acids requirements, resulting in excessive nitrogen excretions. Degradation of these excess proteins could result in production of obnoxious odors. Reducing the crude protein levels of a typical corn-soy based diet and balancing with essential amino acids resulted in more efficient nitrogen utilization by the pig, and less excretion of nitrogenous compounds and odors in manures. Direct measurement of aerial ammonia concentrations from the incubation flasks supported this observation. Similarly, enhancing microbial utilization by fermentation of excess nutrients in the digestive system to alter excretion products may be possible to reduce odorous compounds through proper diet manipulation. Additional work is needed to determine the optimal levels and balance of nutrients for efficient animal growth and microbial utilization to reduce odors, especially from sulfide compounds.

Other methods to improve dietary nutrient digestibilities and efficiencies in pigs are phase-feeding, split-sex feeding, fineness of grind, and pelleting. Diets should be formulated on a nutrient availability basis and adjusted to meet the specific requirements if the genetic lines of the pigs for efficient, profitable performance.

Acknowledgments

A grant in aid provided by the National Pork Producers Council in support of this project is greatly appreciated. Laboratory and surgical assistance by Dr. Judith Nielsen and Mrs. Meredith Cobb on the project is also greatly appreciated.

Table 1. Experimental Diets

¹ Ingredients (amounts/kilogram of premix): vitamin A 6, 098.4 IU; menadione, 1.6 mg; vitamin E, 23.1 IU: vitamin B12, .03 mg; riboflavin, 6.1 mg; d-pantothenic acid, 22.4 mg; and niacin, 34.9 mg.
² Ingredients (milligrams / kilogram of diet): Fe,89.9; Mn, 30; Zn, 75; Cu, 8.75, and I, 1.0
³ Ingredients (milligrams / kilogram of diet): Ca, 370; Se, .29.

Table 2. Effect of diet on pH, nitrogen components and volatile fatty acids in cecal contents.¹

¹ Different letter superscripts within a column are significantly different (P< 0.05).
² TKN = Total Kjeldahl nitrogen.
³ Volatile fatty acids = acetic (Ac), propionic (Pro), isobutyric (iBut), butyric (But), isovaleric (iVal), valeric (Val).

Table 3. Effect of diet on pH, nitrogen components and volatile fatty acids in fresh manure.¹

¹ Different letter superscripts within a column are significantly different (P< 0.05).
² TKN = Total Kjeldahl nitrogen.
³ Volatile fatty acids = acetic (Ac), propionic (Pro), isobutyric (iBut), butyric (But), isovaleric (iVal), valeric (Val).

Table 4. Effect of diet on pH, nitrogen components and volatile fatty acids in anaerobically stored manure.¹

¹ Different letter superscripts within a column are significantly different (P<0.05).
² TKN = Total Kjeldahl nitrogen.
³ Volatile fatty acids = acetic (Ac), propionic (Pro), isobutyric (iBut), butyric (But), isovaleric (iVal), valeric (Val).

Table 5. Effect of diet on bifidobacteria, lactobacilli and total anaerobic bacteria concentrations¹ (Log₁₀ g cells/g cecal contents).

¹ Colonies expressed on wet weight basis.

Index of 1996 Purdue Swine Day Articles

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