J. Anim. Sci. 2003. 81:3211-3215
© 2003 American Society of Animal Science
Diet and evaluators affect perception of swine waste odor: An educational demonstration
A. J. Moeser*,1,
M. T. See*,
E. van Heugten*,
W. E. M. Morrow* and
T. A. T. G. van Kempen*,2
* Department of Animal Science, North Carolina State University, Raleigh, 27695
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Abstract
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An educational program was developed for extension agents, faculty, and graduate students to illustrate the effect of diet composition on odor from swine manure. Participants in this program first received a 2-h detailed review on odorous compounds in manure and the effect of diet on odor. For the second portion of the training, nine manure samples were used from pigs fed diets formulated with feed ingredients predicted to have different effects on odor emission or a nutritionally adequate corn–soybean meal diet. Participants were instructed to rate the odor from these samples for pleasantness, irritation, and intensity on a scale of 0 (best) to 8 (worst), using manure from the corn–soybean meal fed pig as the reference with a score defined as 4 for each variable. Results obtained were summarized and discussed before concluding the program. Participants were Cooperative Extension Agents (n = 13) with swine responsibilities and graduate students and faculty (n = 8). The manure from the diet with the worst odor scores (1% garlic) was rated at 70% more odorous across the three odor variables (P < 0.05) than the diet with the least odorous manure (purified diet). Even though a reference sample was used, individual participants differed in their perception of irritation across samples (P < 0.05), ranging in average score across diets from 2.4 (moderately better than reference) to 5.0 (slightly worse than reference). With extension agents, a 1 to 7 scale (very interesting to not at all interesting) was used for evaluation of the training session. Participants found the material to be interesting (mean = 1.7, SD = 0.7) and the training exercise to be well organized and coherent in its presentation (mean = 1.8, SD = 0.7). Participants enjoyed this training and learned that differences in odor are achievable through altering diet composition, and that the response to swine odor depends on individual odor perception.
Key Words: Extension • Manure • Odor • Pigs • Teaching
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Introduction
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Odors emanating from swine operations are recognized and regulated as a public nuisance in the United States (Miner, 1997
). These odors are a complex array of volatile organic compounds resulting from the fermentative degradation of carbohydrates, fats, and proteins by a variety of indigenous bacterial species present in the large intestine and manure of swine (Zhu and Jacobson, 1999). Therefore, it is likely that diet composition will affect odor emission from swine manure (e.g., high-protein diets increase odorants; Hobbs et al., 1996). However, accurately quantifying odor emission is difficult because individuals experiencing the odor may perceive it differently depending on their previous experiences with the particular odor, but also because of factors such as their mood, health, or age. This may explain why people who work with livestock on a daily basis cannot fully understand the complaints from neighbors who have less exposure to these odors (Shiffman, 1998).
Our objective was to develop a teaching exercise for swine extension agents, graduate students, and faculty in animal science to demonstrate the effect of diet composition on odor emission, and to illustrate the potential for differences in perception of odor among individuals.
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Materials and Methods
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Manure Samples
Manure samples for odor assessment were obtained from nine grower pigs of approximately 50 kg each that were housed in individual concrete pens (1 x 1.5 m). At the start of the experiment, each pig was randomly assigned to one of nine diets. All diets were formulated to contain 17% CP (with the exception of the high-CP diet) using a range of feed ingredients that was expected to impact odor production from manure (Table 1). Animals were allowed ad libitum access to the respective experimental diets and water throughout the 6-d experiment. On d 6 of the experiment, feces and urine were collected from the pigs after the morning feeding and mixed to form a manure-slurry that consisted of a 2:1 urine-to-feces ratio. After homogenous mixing, manure samples labeled by treatment number only were stored in opened Nalgene bottles (Fisher Scientific, Rochester, NY) at room temperature for approximately 24 h until odor assessment by extension agents (n = 13) at an in-service training program. Following evaluation by the extension agents, manure samples were frozen and then thawed approximately 1 mo later. After storage at room temperature for 24 h, samples were evaluated for odor by graduate students and faculty (n = 8) in a swine nutrition seminar.
Odor Exercise
Participants in this exercise first received a 2-h lecture based on Lesson 10 from the Livestock and Poultry Environmental Stewardship curriculum (van Kempen and van Heugten, 2000), which provided a detailed review on odorous compounds in manure and the impact of diet on odor.
Subsequently, the participants were instructed on how to evaluate samples for odor and how to record their findings. The odor evaluation sheet entailed a nominal odor scale with three odor variables (pleasantness, irritation, and intensity) to be evaluated for each sample (Figure 1). This score was based on the method of Schiffman and Williams (1999) and used a scale of 0 to 8 (0 = extremely pleasant, no irritability, or no intensity; 8 = extremely unpleasant, most irritable, and most intense). Evaluators were allowed to sniff the samples and evaluate the odor by comparing it to a reference sample. The reference sample used was manure produced from pigs fed a standard corn–soybean meal diet and was assigned a value of 4 (neutral) on the odor scale.
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Figure 1. Odor evaluation sheet used to assess manure samples. Odor evaluators were asked to assess three odor variables (pleasantness, irritation, and intensity) for each of nine manure samples relative to a control manure sample, which was defined as rating 4 on each scale. Manure samples were stored in 250-mL plastic bottles and were distributed to each evaluator.
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Upon completion of sample evaluation, data were summarized on a blackboard, diet compositions were disclosed, and the findings were discussed. This allowed the participants to learn why samples differed in odor perception and also allowed them to recognize odor characteristics since samples were kept available during this discussion.
Participant Evaluation
At the end of the first session, 11 of the 13 participants completed an assessment form consisting of six questions (Table 2). Responses to the questions were scored on a 1 to 7 Likert-type scale describing the quality, organization, relevance, and usefulness of the exercise, the ability of the material and instructors to stimulate interest, and an assessment of how much they learned from the session. Furthermore, written comments were collected from participants.
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Table 2. Postsession evaluation questions and summary of participating extension agents’ responses for a swine odor teaching exercise. Responses to a Likert-type scale were given a numerical value (1 to 7)
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Statistics
Responses from the odor evaluation sheets were analyzed using conditional ANOVA with the SAS statistical package (Version 8.2, SAS Inst., Inc., Cary, NC). The statistical model included fixed effects of diet and session (agent in-service training or swine nutrition seminar). Participant nested within session was included in the model as a random effect and used as the error term in constructing the F-test for the session effect. Diet x session interaction was not significant and not included in the analysis. Differences among diets and participant means were determined by Tukey’s studentized range test (P < 0.05).
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Results and Discussion
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Effect of Diet Composition on Perceived Odor
It is important to note that the outlined experiment was not designed to result in recommendations for feed formulations that minimize odor. Treatments were not replicated, manure was not collected under circumstances that mimic commercial farms, and diet effects on manure volume and characteristics other than odor that may affect odor emission under field conditions (e.g., stickiness) were ignored. Also, before the second evaluation, manure was frozen. Instead, the objective was to teach the participants about the nature of odor and possible dietary effects on odor. Nevertheless, diet composition resulted in a range of odor scores for manure (Table 3). The diet that yielded manure with the worst odor contained 1% garlic powder. Odor scores for this manure were worse by 56% for pleasantness, 103% for irritation, and 50% for intensity than for manure from the purified diet, which received the lowest odor scores (P < 0.05).
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Table 3. Pleasantness, irritation, and intensity of odor from manure samples from pigs fed diets varying in ingredient compositiona
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Data from this study concur with others (e.g., Hobbs et al., 1995) that dietary sulfur intake is a major factor influencing odor of manure. Participants rated manure from pigs fed a diet containing 1% garlic high on the odor scale with regard to unpleasantness, irritability, and intensity. Garlic contains volatile sulfur compounds in the form of methanethiol, allyl mercaptan, and allyl methyl sulfide, which are thought to be poorly metabolized by the gut and liver and excreted in the urine (Suarez et al., 1999). Likewise, the high-sulfur diet containing feather meal and gypsum produced manure that ranked among the highest in the odor scoring for pleasantness and irritation. Manure from the fishmeal diet also produced high odor responses, which may be attributable to its relatively high sulfur content, but also to trimethyl amine and oxidation products of n-3 fatty acids (Lin, 1994).
Numerically, the purified diet was ranked as the most pleasant, least irritating, and least intense, which was expected even though effects on manure volume and characteristics that were expected to reduce odor further under field conditions were ignored. The purified diet was composed of cornstarch and casein, both assumed to be completely digested in the small intestine (Nyachoti et al., 1997). The highly digestible nature of this diet, in essence, was expected to minimize odor production by supplying fewer bacterial fermentable substrates in the large intestine.
For the high-protein diet, it was assumed that by increasing the amount of dietary protein twofold (34% vs. 17% protein), urinary ammonia would be increased, which is a major irritant. Yet participants were unable to detect a difference compared with the reference manure sample. This may well be an artifact of the experimental design since urine and feces were mixed in fixed ratios; increased nitrogen (urea) excretion is expected to increase urinary volume, possibly without major effects on the concentration of urea (N. L. Trottier, personal communication).
Effect of Session and Evaluator on Perceived Odor From Swine Manure
Differences in perception of odor by individuals are partly dependent on previous experiences with the particular odor. For example, people who are exposed to livestock odors on a daily basis may not consider this odor to be a nuisance or a threat to their health. On the other hand, communities with neighboring swine farms, which have intermittent exposure to these types of odors, often perceive them as strong and offensive, and this has resulted in numerous lawsuits in recent years (Schiffman, 1998).
In this study, individual participants differed in their perception of irritation (P < 0.01) as well, ranging in average score across diets from 2.4 (moderately better) to 5.0 (slightly worse) (Table 4). The extension agent group (SD = 0.8) was more variable in their average perception of irritation than were the graduate students and faculty (SD = 0.4). A subjective evaluation of these data suggested that samples with extreme pleasantness appeared to be rated as more extreme by those with less exposure to odor. However, since participants were not surveyed for odor exposure, a firm conclusion could not be drawn. Exercises like this may thus yield more interesting data if participant exposure were rated (e.g., daily, weekly, monthly).
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Table 4. Main effect means for participants within session and session for pleasantness, irritation, and intensity score of odor from manure samples from pigs fed nine diets varying in ingredient compositiona
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It should be noted that there was a significant correlation between the three odor variables, with Pearson’s correlation coefficients ranging from 0.64 to 0.70 (P < 0.05). Although it is possible that these odor variables responded in tandem to changes in diet composition, it is more likely that these correlations are a result of using an untrained panel for evaluation odors. Thus, panelist may not have been discriminating enough in distinguishing irritation, pleasantness, and intensity.
Evaluation of the Exercise by Extension Agents
Overall, this exercise was determined to be of high quality, well organized, and an interesting educational tool (Table 2
) for teaching about odor. Although participants found the exercise to be relevant to their needs and felt it would be useful in the future, these responses were lower and more variable than the responses to questions one to three. The increased variation in response to questions four and six is likely a reflection on the extent of each individual’s role in interacting with the swine industry and involvement in issues surrounding swine odor. Most of the agents that participated are not involved in nutrition decisions at the farm. Instead, their involvement is mainly to aid with paperwork dealing with waste management. Written comments from participants indicated an appreciation for the participatory nature of the activity and indicated that they enjoyed this exercise.
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Implications
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Malodor from swine production sites is a predominant socioeconomic issue in the swine industry. However, the complexities of odor perception pose a problem when attempting to validate odor nuisance complaints. If teachers and extension professionals in animal science wish to clearly demonstrate that factors such as diet composition and individual perception affect perceived odor emission, they could consider using an odor comparison exercise.
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Footnotes
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1 Current address: College of Veterinary Medicine, North Carolina State University. 
2 Correspondence: 123 Polk Hall (phone: 919-515-4016; fax: 919-515-7780; E-mail: t_vankempen{at}ncsu.edu).
Received for publication February 10, 2003.
Accepted for publication August 4, 2003.
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Literature Cited
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Hobbs, P. J., T. H. Misselbrook, and B. F. Pain. 1995. Assessment of odors from livestock wastes by photoionization detector, an electronic nose, olfactory and gas-chromatography-mass spectometry. J. Agric. Eng. Res. 60:137–144.
Hobbs, P. J., B. F. Pain, R. M. Kay, and P. A. Lee. 1996. Reduction of odorous compounds in fresh pig slurry by dietary control of crude protein. J. Sci. Food Agric. 71: 508–514.
Lin, C. F. 1994. Flavor chemistry of fish oil. Pages 208–232 in ACS Symposium Series. Am. Chem. Soc., Washington, DC.
Miner, R. J. 1997. Nuisance concerns and odor control. J. Dairy Sci. 80:2667–2672.[Abstract]
Nyachoti, C. M., C. F. M. de Lange, B. W. McBride, and H. Schulze. 1997. Significance of endogenous gut nitrogen losses in the nutrition of growing pigs: A review. Can. J. Anim. Sci. 77:149–163.
Schiffman, S. S. 1998. Livestock odors: Implications for human health and well-being. J. Anim. Sci. 76:1343–1355.[Abstract/Free Full Text]
Schiffman, S. S., and C. M. Williams. 1999. Evaluation of swine odor control products using human odor panels. Pages 110–118 in Proc. Anim. Waste Manag. Symp., North Carolina State Univ., Raleigh.
Suarez, F., J. Springfield, J. Furne, and M. Levitt. 1999. Differentation of mouth versus gut as site of origin of odiferous breath gases after ingestion. Am. J. Physiol. 276:425–430.
van Kempen, T., and E. van Heugten. 2000. Reducing pig waste and odor through nutritional means. Lesson 10 in USDA/EPA National Manure Stewardship Curriculum. USDA, Washington, D.C.
Zhu, J., and L. D. Jacobson. 1999. Correlating microbes to major odorous compounds in swine manure. J. Environ. Qual. 28:737–744.[Abstract/Free Full Text]
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Abstract
Introduction
