J APPL POULT RES 2006. 15:531-537
© 2006 Poultry Science Association
Effects of In-House Composting of Litter on Bacterial Levels
K. S. Macklin1,
J. B. Hess,
S. F. Bilgili and
R. A. Norton
Department of Poultry Science, Auburn University, Auburn, AL 36849
1 Corresponding author: macklks{at}auburn.edu
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SUMMARY
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Placing 1-d-old chicks on used litter may lead to unexpected health problems due to high bacteriological counts. Composting litter between flocks is one possible method of decreasing bacteriological counts. At the end of two 7-wk broiler growouts, in-house composting of pine shaving litter was performed, and bacterial counts were taken. In the first trial, composted pine shavings attained an internal temperature of 55°C that lasted for 40 h. After the initial temperature gain, the composted litter maintained a steady temperature of 35°C. Aerobic and anaerobic bacterial counts were lower in composted vs. uncomposted litter. Moisture content was lower in the uncomposted pile than the compost pile. Water activity was higher in the composted pile than in the uncomposted litter. Among the 8 treatments in the second trial, litter that was composted, wetted, and covered achieved the highest internal temperatures of >50°C, which was sustained until trial termination (7 d). The other treatments did not achieve a temperature increase of this magnitude and, if not wetted, the observed temperature increase lasted <24 h. In litter that had been composted for 1 wk, moisture content was lower regardless of treatment. Water activity was highest in treatments that had water added and that were not covered. Composted, covered, not wetted pine shavings produced the lowest aerobic and anaerobic bacterial counts. The results of these 2 trials show that in-house composting of pine shaving litter can reduce bacterial counts, especially when the compost pile is covered.
Key Words: bacterial count • compost • in-house
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DESCRIPTION OF PROBLEM
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Composting of poultry litter is a common practice after litter has been removed from a broiler chicken house. When composting is performed properly, the biodegradable waste is transformed into a stable, relatively odorless compost product. This product is devoid of harmful bacteria and can be safely used to augment nutrients in the soil. Additionally, it is known that composting is an efficient method for the destruction of pathogenic microorganisms [1].
Between flocks, bacterial numbers in litter can be reduced either by desiccation that occurs naturally or by the addition of a litter treatment. Desiccation of the litter, though of no cost to the grower, may not maximize the potential bacterial reduction and does not insure that bacteria are reduced. Conversely, some litter treatments have been shown [2] to significantly reduce bacterial numbers and to decrease or eliminate the number of pathogenic bacteria. However, the use of litter treatments adds an extra financial burden to the grower. A possible alternative in reducing the bacterial numbers is in-house composting of the litter between flocks. Composting between flocks, though labor intensive, would be a safe alternative that can reduce bacterial numbers.
Little research has been done on in-house composting [3, 4, 5, 6], and it was the goal of these trials to determine if this technique is efficient in reducing bacterial numbers. To determine this, 2 trials were performed in which composted vs. uncomposted pine shaving litter was compared. Moisture levels, water activity, and aerobic and anaerobic bacterial counts were measured. In addition to comparing composted vs. uncomposted litter in the second trial, additional treatments measuring the effects of adding water to the composted piles were measured. This was performed to determine if this additional step increased the efficacy of bacterial reduction.
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MATERIALS AND METHODS
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Litter History
Trials were run in pens that contained used pine shaving litter that in trials 1 and 2 had 3 and 4 total flocks reared on it, respectively. Each 4.7 x 2.3 m packed dirt floor pen had been used previously in a production experiment that consisted of 50 birds/pen. Birds were reared under nonstressed conditions and given appropriate feed for a total of 7 wk. One day after the termination of the production experiment, the litter was used in these trials.
Trial 1: Experimental Treatments
After bird removal, composting of the litter was performed in 4 pens. This was accomplished by piling the litter in the middle of the pen, then covering it with a nonbreathable polymesh tarp. The purpose of using a tarp was to trap as much heat and moisture to assist in the composting process. The litter was piled in the middle of the pen to a depth of approximately 0.9 m, with a width of 1.0 to 1.5 m.
Trial 2: Experimental Treatments
After bird removal, each of the 8 pens (4.7 x 2.3 m) was divided to give 16 work areas (2.35 x 1.15 m each). These work areas were then treated in 1 of 8 possible ways (Table 1
). Half of the pens were either composted at a depth of 0.9 m with a base width of 0.5 to 0.7 m or not composted. Half of the composted and half of the uncomposted pens then had 7.6 L of water added. Water was added to increase the moisture content in the litter with the goal of this assisting in temperature gain. A nonbreathable polymesh tarp was then placed in half of the groups. This produced a total of 2 replicates for each treatment.
Temperature Readings
Ambient temperature and compost litter temperature were taken every 4 h for the first trial and every 6 h in the second trial using a temperature squirrel [7]. Compost pile temperature readings were taken by placing the temperature probe approximately 30 cm into the center of the compost pile.
Sample Collection
For the first trial, litter samples were collected at the time of bird removal (time 0) and 2 wk later (time 14) from each pen. In the second trial, litter was collected at the time of bird removal (time 0) and 1 wk later (time 7). Collection of uncomposted litter in both trials was performed in 3 areas within each pen. In trial 1, composted pens had samples collected from 2 areas on the top and 2 areas at a depth of at least 30 cm into the compost pile. Trial 2 had samples taken from 2 areas in the compost pile at a depth of at least 30 cm.
Moisture Content
For each litter sample, 1 g was weighed and placed in a drying oven overnight at 150°C. The following day, the dried samples were weighed and the percentage of moisture determined.
Water Activity
Water activity (Aw) was performed by placing approximately 1 gal of litter into a Aw meter [8]. The number that was present when the meter became stable was recorded.
Litter Microbiology
Populations of aerobic and anaerobic bacteria were enumerated for each pen. This was performed by diluting the samples 1:10 in sterile filter bags with sterile physiological saline (0.85% NaCl). These bags were then placed in a stomacher [9] for 1 min. After being stomached, this 1:10 dilution was serially diluted in sterile physiological saline until a final dilution of 1:100,000,000 was obtained. Dilutions were then spiral-plated using a spiral plater [10] in triplicate onto 2 different media types. The media utilized were plate count agar (PCA) [11] and reduced blood agar (RBA) [12]. The plates were incubated under the following conditions: PCA was incubated aerobically at 37°C, and RBA was incubated at 37°C in an anaerobic chamber [13] containing 5% CO2, 5% H2, and 90% N2. After 24 h, colonies were quantified on a digital plate reader [14], and, using the software included with the plate reader, the average bacterial count for each media was obtained.
Statistical Analysis
Before analysis, bacterial counts on PCA and RBA were transformed from colony-forming units per gram using log10 transformation. These data were then analyzed, comparing the initial bacterial counts to the final bacterial counts using a T-test (P < 0.05). Moisture content results were collected as a percentage; however, for an accurate statistical analysis, these percentages were transformed using arcsine. These transformed numbers, as well as the actual numbers from the Aw results, were compiled for each treatment and analyzed using a T-test (P < 0.05), in which the initial readings were compared with the final readings [15].
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RESULTS AND DISCUSSION
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Litter temperatures were measured for both trials, and the results are presented in Figures 1 and 2. For trial 1 (Figure 1), compost internal temperature attained 50°C by 32 h. This temperature or higher was maintained for 32 h, after which it decreased steadily for the remainder of the monitored period. In trial 2, the temperatures for 2 of the uncomposted piles (treatments A and B) never exceeded ambient temperature (data not shown). In Figure 2, the uncomposted treatment that was supplemented with water and covered with a tarp (C) had typically a 5 to 10°C increase in temperature over the ambient readings. The uncomposted treatment that was supplemented with water and not covered with a tarp (D) typically had a 5°C increase that lasted for 48 h. The 4 composted treatments in this trial attained 50°C by 42 h and maintained at least this temperature for 12 h. The addition of water in treatments C, D, G, and H only produced an increase in temperature when the treatment included the use of a tarp (C and G). Because the use of a nonbreathable polymesh tarp was used, this increase in temperature could be due to the retention of water by the compost pile. This inhibition allowed the litter to maintain a higher moisture content, which should lead to higher temperatures. Final moisture content was higher in the 4 treatments that were covered with a tarp (A, C, E, and G; Table 2); however, in figure 2, only treatment G was able to maintain a high internal temperature.
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Figure 2. Temperature readings (°C) of 7 of the treatments in trial 2. Each mark on the X-axis represents a 24-h interval that temperature was taken. C = uncomposted, water added, covered; D = uncomposted, water added, uncovered; E = composted, no water added, covered; F = composted, no water added, uncovered; G = composted, water added, covered; H = composted, water added, uncovered.
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Table 2
shows the moisture content and Aw that was associated with composted vs. uncomposted litter for both trials. The first trial had no difference in moisture content among the 3 treatments. In the second trial, all 8 treatments had a reduction in moisture content after 1 wk. Unlike trial 1, moisture content levels decreased significantly in all 4 of the composted treatments, with 3 of the 4 having a statistically significant decrease. The only exception was the composted pile that had water added and was covered (treatment G).
A good measure of bacterial activity, as well as odor, is Aw. Water activity is the measurement of how tightly water is bound to a substrate, in this case the pine shavings. Eriksson de Rezende et al. [16] have shown that an Aw <0.85 is inhospitable to bacteria. In general, the lower the Aw, the less bacteria present; this reduction in bacteria typically leads to less odor being produced. The Aw for trial 1 showed that composted litter had no change in Aw when comparing the initial Aw level to the measurement that was taken 2 wk later. However, in this trial, uncomposted litter had a significant decline in Aw. This decline in Aw did not lead to a significant decrease in aerobic bacterial numbers for the uncomposted litter (Figure 3); however, the 2 composted treatments had significant bacterial reductions with no change in Aw. The Aw levels for trial 2 were, in general, lower. The only exceptions were 2 of the treatments that were wetted only (D and H). Unlike the first trial, in which covered composted litter had no change in its Aw, all 4 covered treatments had lower Aw after 1 wk, with treatment C having statistically significant lower Aw measurements. In this trial, there was more of a correlation between Aw and bacterial numbers. The 2 treatments (D and H) that had an Aw >0.85 had slightly higher aerobic bacterial counts than the other 6 treatments (Figure 4) after 1 wk. In these 2 trials, Aw was not an accurate measure of bacterial levels. This is probably due to the complex nature of used poultry litter.
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Figure 3. Aerobic bacterial counts (log10) for trial 1. Time 0 is initial sampling, and time 2 is sampling performed 2 wk later. Statistical differences at P < 0.01 are denoted by double asterisks (**).
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Figure 4. Aerobic bacterial counts (log10) for all 8 treatments for trial 2. Time 0 is initial sampling, and trial 1 is sampling performed 1 wk later. A = uncomposted, no water added, covered; B = uncomposted, no water added, uncovered; C = uncomposted, water added, covered; D = uncomposted, water added, uncovered; E = composted, no water added, covered; F = composted, no water added, uncovered; G = composted, water added, covered; H = composted, water added, uncovered. Statistical difference at P < 0.05 is signified by an asterisk (*).
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Overall aerobic and anaerobic bacterial counts for trial 1 were lower in composted litter regardless of where samples were taken (Figures 3 and 5). The decrease for aerobic bacteria was 1 logarithm and for anaerobic bacteria 2 logarithms. Anaerobic bacterial levels decreased even in the uncomposted piles for trial 1. For the second trial, aerobic bacteria (Figure 4) were significantly lower only in treatment E. Interestingly, this treatment was piled and covered. Most of the treatments lowered the anaerobic bacterial numbers (Figure 6). The lone exception is treatment B, which was the untreated control. The results from the 2 trials show that covering the compost pile is an effective way to reduce bacterial numbers. The observation about a reduction in anaerobic numbers using in-house composting had been observed previously [6].
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Figure 5. Anaerobic counts (log10) for trial 1. Time 0 and 2 represent initial and counts taken 2 wk later. Statistical differences between sampling times are expressed using a single asterisk (*) for P < 0.05 and double asterisks (**) for P < 0.01.
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Figure 6. Anaerobic counts for all 8 treatments for trial 2. Time 0 signifies initial samples, with time 1 signifying samples taken 1 wk later. A = uncomposted, no water added, covered; B = uncomposted, no water added, uncovered; C = uncomposted, water added, covered; D = uncomposted, water added, uncovered; E = composted, no water added, covered; F = composted, no water added, uncovered; G = composted, water added, covered; H = composted, water added, uncovered. Statistical differences between the 2 times are differentiated using a single asterisk (*) for P < 0.05 and double asterisks (**) for P < 0.01.
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The results presented show that in-house composting of litter for 1 wk using a non-breathable polymesh tarp to cover the pile reduces total aerobic and anaerobic bacterial numbers. These 2 trials were performed for different lengths of time. The data presented imply that the majority of bacterial reduction using this method is complete after 1 wk. An additional week did not reduce the bacterial numbers any further. As is shown in both trials, the addition of the tarp resulted in a significant reduction of bacterial numbers.
For a compost pile to work effectively, the temperature must rise above 50°C and be maintained at that temperature for at least 1 d to kill bacteria [1, 17]. Typically, a compost pile is mixed every few days. Mixing introduces O to the bacteria, allowing them to further break down organic material in the compost and to generate heat. In these 2 trials, mixing was not performed. If it had been, there might have been a greater reduction in overall bacterial numbers because the internal temperature of the compost pile would have been maintained at a higher temperature for a longer period of time. The primary reason why mixing wasn’t performed is that in-house composting must be shown to be practical to perform for a typical commercial poultry grower. As observed in Figures 1 and 2, all of the litter that was composted attained 50°C by 42 h. The significance of attaining this temperature is not only important for killing bacteria, it is also at this temperature that most viruses, fungi, and parasitic eggs are killed [1, 17].
In addition to the heat that was produced in the compost piles, ammonia may have played a role in bacterial reduction. The treatments that had the highest level of bacterial reduction involved the use of a nonbreathable polymesh tarp to cover the pile. An observation that was noted throughout this trial was that ammonia was more noticeable in the treatments that included the addition of a tarp. The tarp may have acted as an impermeable barrier that allowed ammonia to build up in the compost pile and assisted in decreasing the bacterial numbers. The only exception to this hypothesis is seen with aerobic bacteria in Figure 4 with treatment G. The only difference from this treatment and the other similar treatment (E) is that water was added. Perhaps the addition of water diluted the toxic affects of ammonia, thus allowing the bacteria to survive. Further research needs to be performed to determine the levels of ammonia that are being produced in these compost piles and if they are contributing to reducing bacterial numbers.
It is also interesting to note that bacterial counts from the top of the compost pile in trial 1 were just as low as the samples taken from the middle of the compost pile. The addition of the tarp may have allowed ammonia to build up to a toxic level for the bacteria or it may have trapped some of the internal heat to affect the top of the compost pile. Because the temperature was not measured at the top of the compost pile, it is difficult to confirm if this supposition is true.
Given the trend by the poultry industry to minimize downtime between flocks (<14 d), it appears that in-house composting of litter may be a practical method to reduce bacterial numbers.
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CONCLUSIONS AND APPLICATIONS
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- In-house composting of litter between flocks is an effective way of reducing bacterial levels. These trials demonstrate that 1 wk of in-house composting is sufficient to see a significant decrease in bacteria.
- Covering of the in-house compost pile is recommended in reducing bacterial numbers.
- The addition of water to the litter does not appear to aid in bacterial reduction.
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REFERENCES AND NOTES
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- Dumontet, S., H. Dinel, and S. B. Baloda. 1999. Pathogen reduction in sewage sludge by composting and other biological treatments: A review. Biol. Agric. Hortic. 16:409–430.
- Pope, M. J., and T. E. Cherry. 2000. An evaluation of the presence of pathogens on broilers raised on poultry litter treatment-treated litter. Poult. Sci. 79:1351–1355.[Abstract/Free Full Text]
- Hess, J. B., K. S. Macklin, J. P. Blake, and T. Lavergne. 2005. Managing broiler litter for bird health and performance. 2005 Midwest Poult. Fed. Conv., St. Paul, MN.
- Hess, J. B., K. S. Macklin, and S. F. Bilgili. 2005. Disease suppression and performance enhancement through litter composting between flocks. Ala. Poult. Mon. 5:7.
- Hess, J. B., K. S. Macklin, and S. F. Bilgili. 2005. Litter composting in-house. Ala. Poult. Mon. 5:7.
- Lavergne, T., W. A. Carney Jr., and D. A. Schellinger. 2005. Making poultry litter safe for re-use: In-house pasteurization. La. Agric. 47:10–11.
- Grant Instruments Squirrel SQ800 data logger, Grant Instruments (Cambridge) Ltd., Cambridgeshire, UK.
- AquaLab Series 3, Decagon Devices Inc., Pullman, WA.
- Easy Mix, Microbiology Int., Frederick, MD.
- DW spiral platter, DW Scientific, Microbiology Int., Frederick, MD.
- Difco Laboratories, Detroit, MI.
- BD Biosciences, Sparks Glencoe, MD.
- Bactron IV, Shel Lab, Cornelius, OR.
- ProtoCol, Microbiology Int.
- SPSS for Windows, Release 12.0, SPSS Inc., Chicago, IL.
- Eriksson de Rezende, C. L., E. T. Mallinson, A. Gupte, and S. W. Joseph. 2001. Salmonella spp. are affected by different levels of water activity in closed microcosms. J. Ind. Microbiol. Biotechnol. 26:222–225.[Web of Science][Medline]
- Jones, P., and M. Martin. 2003. A Review of the Literature on the Occurrence and Survival of Pathogens of Animals and Humans in Green Compost. WARP Standards Report. WARP, Oxon, UK.
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TOP
SUMMARY
DESCRIPTION OF PROBLEM
) and compost (
) temperatures for trial 1. Each mark on X-axis indicates a 24-h time interval.