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Fermentation characteristics of integral cassava tuber meal ensiled with swine waste
Biological Wastes 28 (1989) 293-301
Fermentation Characteristics of Integral Cassava Tuber Meal Ensiled With Swine Waste G. Iniguez Covarrubias, Ma. de J. Franco Gomez, V. Ruiz. Carrera Centro de Investigacion y de Estudios Avanzados del I.P.N. Departmento de Biotecnologia y Bioingenieria, Apartado Postal 14-740, 07360 Mexico, D.F., Mexico
&
T. A. McCaskey* Department of Animal and Dairy Sciences and Alabama Agricultural Experiment Station, Auburn University, Alabama 36849, USA (Received 15 October 1987; revised version received 28 October 1988;
accepted 9 November 1988)
ABSTRACT Swine waste was mixed and ensiled with integral cassava tuber meal in the following proportions on a wet basis to obtain about 40% moisture content: 42:58, 53:47, 65:35 and 80:20. The mixtures (1 kg each) were packed in double polyethylene bags 1 mil thick, individually sealed and stored at 28 +_2°C. After fermentation for 42 days, the polyethylene bags were opened and samples from the central part of the bags were analysed to determine proximate composition and fermentation characteristics of the mixture. Acid production in the ensiled mixtures was directly related to the level of tuber meal combined with swine waste. Mixtures with 47 parts or more of tuber meal achieved p H values of 4.5 or less. After fermentation, the 53:47 mixture achieved p H 4.5 and contained 6.6% lactic acid and 2"4% volatile fatty acid ( V F A ) . The proximate composition of the mixture was (dry matter basis) 8"6% crude protein, 7"9% crude fiber, 6% ash, 2"7% ether extract and 74"8% nitrogen-free extract. Mixtures of swine waste and cassava tuber meal might have potential value as an alternate, low-cost feed resource. * To whom correspondence should be addressed. 293 Biological Wastes 0269-7483/89/$03.50 © 1989 Elsevier Science Publishers Ltd. England. Printed in Great Britain
294
G. lniguez Covarrubias et al.
INTRODUCTION The high cost and shortages of traditional feed ingredients during recent years have highlighted the need for alternate sources of feed to support the swine industries of many tropical countries. One feed source which could play an important role in this context is cassava. Cassava tuber meal (CTM) is primarily a source of energy with nitrogen-free extract of about 90% (Oke, 1978) which consists of 80% starch and 20% sugars (Vogt, 1966). The high starch content makes CTM highly digestible for non-ruminant animals. One of the major problems in utilizing C T M in animal feeding is its low protein content when compared with that of corn (Ravindran et al., 1983). The chemical composition of swine waste (Kornegay et al., 1977), especially the high nitrogen content, and the high source of energy of C T M suggest that both resources mixed together would be feasible for animal feeding after an ensilage period in order to destroy potential pathogenic organisms in swine waste. Feed supplemented with wastes should be processed to eliminate the potential risk of disease (McCaskey & Anthony, 1979). Whole corn plant forage and swine waste mixtures have been demonstrated to ferment readily and to achieve acidities that preserve the mixtures and eliminate enteric bacteria (McCaskey et al., 1985). The objective of this work was to study the fermentative and chemical characteristics of integral cassava tuber meal ensiled with varying amounts of swine waste.
METHODS Ensilage was prepared from mixtures of hog manure obtained from a farm in La Piedad, Michoacan, Mexico, combined with dried cassava tuber meal (M-Pan 51 variety) from Huimanguillo, Tabasco, Mexico. The manure was collected from hogs in the final production stage maintained on a diet of 90% cracked sorghum grain and 10% concentrate mix of minerals, vitamins and protein supplement. The manure was collected daily by manually scraping the concrete floor of an entire pen of animals maintained in confinement. The manure consisted of wet fecal solids of about 74% water content. The integral cassava tuber meal (ICTM) was obtained from washed fresh tubers which were chopped in slices 0.2-0-5 cm wide. The slices were dried to 4.5% moisture in a forced-draft oven at a maximum temperature of 60°C for 48 h. After drying, the slices were ground in a Wiley mill through a 1-mm screen. The waste (73% moisture) and the ICTM (4"5% moisture) were ensiled in the following proportions on a wet basis: 42:58, 53:47, 65:35 and 80:20. Swine waste without cassava meal was treated as the control fermentation.
Fermentation o f cassava tuber meal with swine waste
295
In order to obtain about 40% moisture content in all the mixtures, water was added to the waste for the first mixture, and the waste for the last two mixtures was sun-dried. Although drying the waste will add cost, it was deemed necessary to dry the swine waste to avoid undesirable butyric acid fermentations that occur with fermenting waste mixtures of 40% moisture or more. No drying or addition of water to the waste was required to achieve 40% moisture with the 53:47 mixture. Six 1-kg portions of each mixture were packed in doubled polyethylene bags (1 mil thick), which were pressed to expel the air and then individually sealed. The polyethylene bags were stored at 28 + 2°C to promote fermentation of the mixtures. After a fermentation period of 42 days, the polyethylene bags were opened and the appearance and odor of the ensilage were evaluated. Three replicate samples from the central part of each bag were taken and frozen for later analysis. Total nitrogen, dry matter, ether extract and ash were determined by AOAC procedures (1980). Crude fiber was determined by the procedure of Van de Kamer and Van Ginkel (1952). Water-soluble carbohydrate (WSC) content was estimated according to the method of Dubois e t al. (1956) as adapted to corn plants by Johnson et al. (1966). Lactic acid content was determined by the method of Barker & Summerson (1941), and lactic acid buffering capacity of the waste/ICTM mixtures was measured by the procedure of McDonald & Henderson (1962). Levels of VFA were determined by the method of Kroman et al. (1967). Sample preparation for ammonia-nitrogen and titratable acidity determinations was according to the procedure of Jakhmola et aL (1984). The analyses for ammonia-nitrogen and titratable acidity were conducted according to APHA (1980). Sample preparation for pH determination (electrometrically) was according to the procedure of Weiner (1977). The data were subjected to analysis of variance including a linear effect for increasing levels of swine waste (orthogonal polynomial, Steel & Torrie, 1980).
RESULTS A N D DISCUSSION The proximal composition of the integral cassava tuber meal is presented in Table 1. The tuber meal was low in crude protein, fiber, fat and ash content, but high in nitrogen-free extract. The composition was in agreement with values reported by Gerpacio (1979), Khajarern et al. (1977) and Ravindran et al. (1982). However, the swine waste was high in crude protein and relatively low in nitrogen-free extract as previously reported by Kornegay et al. (1977). Mixtures of the two substrates potentially should provide an alternative, low-cost nutrient feed source.
G. Iniguez Covarrubias et al.
296
TABLE 1 Proximal Composition of the Dried Integral Cassava Tuber Meal
AnaO'ses (dry basis) Moisture Crude protein (N × 6'25) Crude fiber Ash Ether extract Nitrogen-free extract a a
% 4-54 2-20 4"59 2.17 0.56 90.48
The nitrogen-free extract was calculated by difference.
Studies conducted by Caswell et aL (1975) with broiler chicken waste and Knight et al. (1977) with beef cattle waste showed that the optimum moisture level for lactic fermentation of these wastes ensiled with conventional feed ingredients is 40%. Mixtures of swine waste and ICTM were prepared to have a moisture content of approximately 40%. The pH of the mixtures before ensiling ranged from 6.3 to 6"6 and the water-soluble carbohydrate levels ranged from 1"9% (dry basis) for the swine waste alone to 11"3% for the highest proportion of tuber meal blended with swine waste (Table 2). After the mixtures were ensiled for 42 days at 28°C, acid was produced in all mixtures including the swine waste ensiled alone. The swine waste without tuber meal achieved a pH of 5.7 after fermentation. Mixtures of tuber meal and waste had lower pH values after ensiling. The mixture containing the highest level of tuber meal (42 parts) achieved the lowest pH (4.2). These results indicate that the addition of tuber meal to swine waste improved the fermentation characteristics of the waste. The biological production of acid is associated with the fermentation of carbohydrates. The data in Table 2 show a direct relationship between the level of WSC in the mixtures with acid development as measured by pH. Lactic acid was produced in all the mixtures but reached highest levels in mixtures containing 20-35 parts of tuber meal. Levels of volatile fatty acids increased with increasing proportions of swine waste in the mixtures. Higher ratios of lactic acid to VFA, which are indicative of good quality silage, were demonstrated in mixtures containing the higher levels of tuber meal. Acid production in the ensiled mixtures was directly related to the level of cassava tuber meal in the mixtures. When the mixtures contained 47 parts or more of cassava meal, acid development as revealed by pH was 4.5 or lower, which is sufficient to preserve-the mixtures and to eliminate most enteric pathogens that might be encountered in the swine waste (Weiner, 1984).
297
Fermentation o f cassava tuber meal with swine waste TABLE 2
Fermentation Characteristics of Varied Levelsof Swine Waste and Integral Cassava Tuber Meal on pH, Water-Soluble Carbohydrates, Volatile Fatty Acids and Lactic Acid Analyses~
Proportions o f swine waste and integral cassava tuber meal (wet basis) 42:58
53:47
65:35
80:20
100
SEM
Before ensiled: Moisture (%) pH WSCb (%) Volatile fatty acids (%) Lactic acid (%) Ratio lactic acid to VFA
40-77 6'32 11.30 0"73 1'09 1.49
37-53 6.64 9-90 1'42 1'35 0.95
38.77 6"52 6"93 2"24 1.54 0.69
39-51 6"58 5-83 3'43 1'94 0.57
39.10 6.55 1.85 4.93 2.10 0.42
0.29 0-01 0.19 0-30 0"10 0.08
After ensiled (42 days): pHc WSCc (%) Volatile fatty acidsc (%) Lactic acidc (%) Ratio lactic acid to VFAc
4.15 32.47 1.54 6'12 3'97
4.48 29"33 2-38 6"57 2'76
4.62 21.62 3.41 8"08 2'37
4.93 13.51 4-88 7"98 1'64
5-68 1-58 5.86 3'58 1.64
0-03 0.31 0-03 0"15 0"11
a Each value represents the mean of three samples. All analysesexcept moisture and pH are expressed on a dry basis. b Water-soluble carbohydrates. c Linear effect of treatment (P < 0.01). On a wet basis, the cassava meal contained about 20% WSC and the swine waste about 1.9%. To achieve a pH of 4.5 or less in the ensiled mixtures, about 10% WSC was required in the swine waste/ICTM mixture. Therefore, the data in Table 2 indicate that about 47 parts of cassava tuber meal are required to achieve a pH of 4.5 or less in the ensiled mixture. The WSC level of the fermented samples increased after the ensilage period, it being higher for those samples with higher cassava tuber meal content. This could be due to the activity of extracellular amylolytic enzymes produced by starchhydrolyzing L a c t o b a c i l l u s . N a k a m u r a & Crowell (1979) isolated several starch-hydrolysing L a c t o b a c i l l u s strains from swine waste-corn fermentation. Langston e t al. (1962) reported that m a n y silage organisms hydrolyse and ferment starch, especially high acid-producing lactobacilli. The lactic acid-buffer capacity (LBC) of the mixtures before fermentation increased with increasing proportions of swine waste in the mixtures (Table 3). Similar results were reported by K a m a r a e t al. (1984) for ensiled cattle waste. It is clear that if animal waste intended for silage has a high buffering capacity, more acid must be produced during fermentation to achieve a low pH to insure the microbial safety of the product. McCaskey & W a n g (1985)
298
G. Iniguez Covarrubias et al. TABLE 3
Lactic Acid BufferCapacity, Titratable Acidity and Ammonia-Nitrogen Levels of Waste and Integral Cassava Tuber Meal Mixtures Analyses~
Before ensiled: Lactic buffer capacity (mg lactic acid/g DM) After ensiled: Titratable acidityb'c (mM acid/100g DM) Ammonia-nitrogen c (% DM) (% Total-N)
Proportions of swine waste and integral cassava tuber meal (wet basis) 42:58
53:47
65:35
80:20
100
SEM
42.22
78-82
112-60
150"15
242"09
0"60
30.62
36.52
44-18
40.77
13-40
0.30
0.08 11.28
0.21 15-69
0.37 17.05
0.65 19.76
1-02 23.68
0.09
a Each value represents the mean of three samples. b Titratable acidity is expressed as mM of lactic acid equivalent in 100g dry matter of mixtures. The samples were titrated with 0"05N NaOH to pH 7. c Linear effect of treatment (P < 0.01). reported a higher LBC for poultry litter silage than for bovine manure silage, and corn silage had the lowest buffering capacity. Animal wastes that have high crude protein levels tend to also have a high acid-buffering capacity. Drying the swine waste to achieve 40% moisture in the 65:35 and 80:20 (waste :meal) blends might have decreased the nitrogen content of these blends. Therefore, ammonia and crude protein contents o f these blends might be higher than reported in this study. Examination o f the ammonia-nitrogen data (Table 3) for the fermented mixtures indicates that swine waste at each level caused an increase in the proportion of ammonianitrogen. The degradation o f nitrogenous substances in the swine waste is the obvious source of the ammonia. H a r m o n et al. (1975) reported that ammonia-nitrogen content o f fermented silages tended to increase with increasing proportions o f broiler litter in the silages. High-quality silages contain high levels of lactic acid relative to volatile acids, a low p H (Langston et al., 1962) and a relatively low level of ammonia-nitrogen, generally less than 15°/0 of the total nitrogen (Nillison, 1956). Although microbiological analyses were not conducted on the ensiled mixtures, the ensiling process has been demonstrated to be an effective method of eliminating undesirable microorganisms. Coliform bacteria in bovine manure-blended rations were eliminated after the rations were ensiled I0 days and reached p H values of 4.7 and 4.5 (Knight et al., 1977).
Fermentation o f cassava tuber meal with swine waste
299
TABLE 4
Proximate Composition of SwineWaste and Integral Cassava Tuber Meal Mixtures After Fermentation Proportions o f swine waste and integral cassava tuber meal (wet basis)
Analyses (dry basis)
Moisture (%) Crude protein b (N × 6.25) (%) Crude fiberb (%) Ash b (%) Ether extract b (%) Nitrogen-free extract "'b (%)
42:58
53:47
65:35
80:20
100
SEM
41.89 4'37 6.00 3.01 0.82 85.80
40.76 8-55 7-93 6-04 2.73 74-75
41.87 13.57 8"67 9.87 4.45 63.44
41-79 20-56 11-64 13"64 6.80 44"05
38.73 26.81 13.72 18"18 11.13 30'16
0'12 0.43 0-29 0'25 0.19 0'75
" The nitrogen-free extract was calculated by difference.
b Linear effectof treatment (P < 0.01).
Salmonella typhimurium, Escherichia coli and species of Mycobacterium were eliminated from bovine manure silage when the pH decreased to 4.5 or less (McCaskey & Shehane, 1980; McCaskey & Wang, 1985). Fermentation of bovine manure-feed mixtures to a pH of about 4"5 or less will eliminate Brucella abortus if the organism is present in manure (McCaskey, 1985). In this study, mixtures of swine waste and tuber meal that contained 47 parts or more tuber meal had pH values of 4-5 or less after the ensiling process (Table 2). The proximate composition of the ensiled swine waste and tuber meal mixtures is shown in Table 4. The crude protein levels of the mixtures ranged from 4.4% to 20-56% (dry basis) and were directly related to the level of swine waste in the ensiled mixtures. Similar trends were observed for crude fiber, ash and ether extract. The ensiled mixture (53 parts waste to 47 parts tuber meal) that achieved just under pH 4-5 contained 8-6% crude protein, 7.9% crude fiber, 6% ash and 2-7% ether extract. This mixture represents the highest nutrient level that should be considered safe from zoonotic diseases. This study demonstrated that ICTM can be used as a carbohydrate source to improve the fermentation of swine waste. At a ratio of 53:47 wet basis (swine waste to cassava tuber meal), the mixture with 40% moisture achieved pH 4.5 which has been demonstrated with ensiled animal waste mixtures to be sufficient acidity to preserve the mixture and eliminate potential pathogens such as Salmonella (McCaskey et aL, 1985). Swine waste treated and preserved by fermentation with cassava tuber meal might serve as a process to convert these available resources into a low-cost, alternate feed source.
300
G. Iniguez Covarrubias et al. ACKNOWLEDGEMENTS
The authors express thanks to Consejo del Sistema Nacional de Educacion Tecnologica (COSNET, Mexico) for financial support o f this study, and to the faculty at A u b u r n University who edited the manuscript. Special thanks is given to Sarah H u n t who typed the manuscript.
REFERENCES APHA (1980). Standard Methods for the Examination of Water and Wastewater (14th edn). American Public Health Association, New York. AOAC (1980). Official Methods of Analysis (llth edn). Association of Official Analytical Chemists, Washington, DC. Barker, S. B. & Summerson, W. H. (1941). The colorimetric determination of lactic acid in biological materials. J. Biol. Chem., 38, 535. Caswell, L. F., Fontenot, J. P. & Webb, K. E., Jr (1975). Ensiled broiler litter with different moisture levels. J. Anim. Sci., 40, 200. Dubois, M., Gilles, K. A., Hamilton, J. K., Rebers, P. A. & Smith, F. (1956). Colorimetric method for determination of sugars and related substances. Anal Chem., 28, 350. Gerpacio, A. L. (1979). The influence of cassava and sweet potato root meal on the availability of nutrients in mixed broiler rations and broiler performance. ASPAC Tech. Bull. No. 43. Taipei, Taiwan. p. 13. Harmon, B. W., Fontenot, J. P. & Webb, K. E., Jr (1975). Ensiled broiler litter and corn forage. I. Fermentation chracteristics. J. Anon. Sci., 40, 144. Jakhmola, R. C., Kamra, D. N., Rameshwar Singh & Pathak, N. N. (1984). Fermentation of cattle waste for animal feeding. Agric. Wastes, 10, 229. Johnson, R. R., Balwani, T. L., Johnson, L. J., McClure, K. E. & Dehority, B. A. (1966). Corn plant maturity. II. Effect on 'in vitro' cellulose digestibility and soluble carbohydrate content. J. Anim. Sci., 25, 617. Kamara, D. N., Jakhmola, R. C. & Rameshwar Singh (1984). Ensiling of cattle waste and wheat straw with or without green maize. Agric. Wastes, 9, 309. Khajarern, S., Khajarern, J. M., Kitpanit, N. & Muller, Z. O. (1977). Cassava in the nutrition of swine. In Cassava as Animal Feed. Proceedings of a workshop. University of Guelph, Ontario, pp. 56--64. Knight, E. F., McCaskey, T. A., Anthony, W. B. & Waiters, J. C. (1977). Microbial populations changes and fermentation characteristics of ensiled bovine manure-blended rations. J. Dairy Sci., 60, 416. Kornegay, E. T., Holland, M. R., Webb, Jr, K. E., Bovard, K. P. & Hedges, J. D. (1977). Nutrient characterization of swine fecal waste and utilization of these nutrients by swine. J. Anim. Sci., 44, 608. Kroman, R. P., Mayer, J, H. & Stielan, W. J. (1967). Steam distillation of volatile fatty acids in rumen ingesta. J. Dairy Sci., 50, 73. Langston, C. W., Wiseman, H. G., Gordon, C. H., Jacobson, W. C., Melin, C. G., Moore, L. A. & McCalmont, J. R. (1962). Chemical and bacteriological changes in grass silage during the early stages of fermentation. I. Chemical changes. J. Dairy Sci., 45, 396.
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McCaskey, T. A. (1985). Evaluation of the ensiling process to achieve safety from Brucella abortus in cattle manure-feed mixtures. In Agricultural Waste Utilization and Management (Proceedings 5th International Symposium on Agricultural Wastes). American Society of Agricultural Engineers, St Joseph, Michigan, pp. 167-174. McCaskey, T. A. & Anthony, W. B. (1979). Human and animal health aspects of feeding livestock excreta. J. Anita. Sci., 48, 163. McCaskey, T. A. & Shehane, J. D. (1980). Lactic acid fermentation reduces risk of mycobacteria transmission by bovine manure-formulated rations. In Livestock Waste: A Renewable Resource (Proceedings 4th International Symposium Livestock Wastes). American Society of Agricultural Engineers, St Joseph, Michigan, p. 73. McCaskey, T. A. & Wang, Y. D. (1985). Evaluation of the lactic acid fermentation process for elimination of mycobacteria from wastelage. J. Dairy Sci., 68, 1401. McCaskey, T. A., Sutton, A. L., Lincoln, E. P., Dobson, D. C. & Fontenot, J. P. (1985). Safety aspects of feeding animal wastes. In Agricultural Waste Utilization and Management (Proceedings 5th International Symposium on Agricultural Wastes). Amercan Society Agricultural Engineers, St Joseph, Michigan, p. 275. McDonald, P. & Henderson, A. R. (1962). Buffering capacity of herbage samples as a factor in ensiling. J. Sci. Fd Agric., 13, 395. Nakamura, L. K. & Crowell, C. D. (1979). Lactobacillus amylophilus. A new starchhydrolyzing species from swine waste-corn fermentation. In Developments in Industrial Microbiology (Proceedings of the Thirty-fifth General Meeting). Society for Industrial Microbiology, 20, p. 531. Nillison, R. (1956). Quoted in Herbage Abstracts, 30, 1-8. Oke, O. L. (1978). Problems in the use of cassava as animal feed. Anita. Feed Sci. Tech., 3, 345. Ravindran, V., Kornegay, E. T., Webb, K. E., Jr & Rajaguru, A. S. B. (1982). Nutrient characterization of some feedstuffs of Sri Lanka. J. Natl. Agric. Soc. Ceylon, 19, 19. Ravindran, V., Kornegay, E. T. & Rajaguru, A. S. B. (1983). Utilization of the whole cassava plant as swine feed. World Rev. Anim. Prod., 19(1), 7-14. Steel, R. D. G. & Torrie, J. H. (1980). Principles and Procedures of Statistics. A Biometrical Approach. McGraw-Hill, Toronto. Van de Kamer, S. H. & Van Ginkel, L. (1952). Rapid determination of crude fiber in cereal. Cereal Chem., 29, 239. Vogt, H. (1966). The use of tapioca meal in poultry rations. Wld Poultry Sci. J., 22, 113. Weiner, B. A. (1977). Characteristics of aerobic, solid substrate ferementation of swine waste-corn mixtures. Eur. J. Appl. Microbiol., 4, 51. Weiner, B. A. (1984). Swine waste-corn silage and the survival of dysentery bacteria. Trans. ASAE, 27, 177.
Fermentation Characteristics of Integral Cassava Tuber Meal Ensiled With Swine Waste G. Iniguez Covarrubias, Ma. de J. Franco Gomez, V. Ruiz. Carrera Centro de Investigacion y de Estudios Avanzados del I.P.N. Departmento de Biotecnologia y Bioingenieria, Apartado Postal 14-740, 07360 Mexico, D.F., Mexico
&
T. A. McCaskey* Department of Animal and Dairy Sciences and Alabama Agricultural Experiment Station, Auburn University, Alabama 36849, USA (Received 15 October 1987; revised version received 28 October 1988;
accepted 9 November 1988)
ABSTRACT Swine waste was mixed and ensiled with integral cassava tuber meal in the following proportions on a wet basis to obtain about 40% moisture content: 42:58, 53:47, 65:35 and 80:20. The mixtures (1 kg each) were packed in double polyethylene bags 1 mil thick, individually sealed and stored at 28 +_2°C. After fermentation for 42 days, the polyethylene bags were opened and samples from the central part of the bags were analysed to determine proximate composition and fermentation characteristics of the mixture. Acid production in the ensiled mixtures was directly related to the level of tuber meal combined with swine waste. Mixtures with 47 parts or more of tuber meal achieved p H values of 4.5 or less. After fermentation, the 53:47 mixture achieved p H 4.5 and contained 6.6% lactic acid and 2"4% volatile fatty acid ( V F A ) . The proximate composition of the mixture was (dry matter basis) 8"6% crude protein, 7"9% crude fiber, 6% ash, 2"7% ether extract and 74"8% nitrogen-free extract. Mixtures of swine waste and cassava tuber meal might have potential value as an alternate, low-cost feed resource. * To whom correspondence should be addressed. 293 Biological Wastes 0269-7483/89/$03.50 © 1989 Elsevier Science Publishers Ltd. England. Printed in Great Britain
294
G. lniguez Covarrubias et al.
INTRODUCTION The high cost and shortages of traditional feed ingredients during recent years have highlighted the need for alternate sources of feed to support the swine industries of many tropical countries. One feed source which could play an important role in this context is cassava. Cassava tuber meal (CTM) is primarily a source of energy with nitrogen-free extract of about 90% (Oke, 1978) which consists of 80% starch and 20% sugars (Vogt, 1966). The high starch content makes CTM highly digestible for non-ruminant animals. One of the major problems in utilizing C T M in animal feeding is its low protein content when compared with that of corn (Ravindran et al., 1983). The chemical composition of swine waste (Kornegay et al., 1977), especially the high nitrogen content, and the high source of energy of C T M suggest that both resources mixed together would be feasible for animal feeding after an ensilage period in order to destroy potential pathogenic organisms in swine waste. Feed supplemented with wastes should be processed to eliminate the potential risk of disease (McCaskey & Anthony, 1979). Whole corn plant forage and swine waste mixtures have been demonstrated to ferment readily and to achieve acidities that preserve the mixtures and eliminate enteric bacteria (McCaskey et al., 1985). The objective of this work was to study the fermentative and chemical characteristics of integral cassava tuber meal ensiled with varying amounts of swine waste.
METHODS Ensilage was prepared from mixtures of hog manure obtained from a farm in La Piedad, Michoacan, Mexico, combined with dried cassava tuber meal (M-Pan 51 variety) from Huimanguillo, Tabasco, Mexico. The manure was collected from hogs in the final production stage maintained on a diet of 90% cracked sorghum grain and 10% concentrate mix of minerals, vitamins and protein supplement. The manure was collected daily by manually scraping the concrete floor of an entire pen of animals maintained in confinement. The manure consisted of wet fecal solids of about 74% water content. The integral cassava tuber meal (ICTM) was obtained from washed fresh tubers which were chopped in slices 0.2-0-5 cm wide. The slices were dried to 4.5% moisture in a forced-draft oven at a maximum temperature of 60°C for 48 h. After drying, the slices were ground in a Wiley mill through a 1-mm screen. The waste (73% moisture) and the ICTM (4"5% moisture) were ensiled in the following proportions on a wet basis: 42:58, 53:47, 65:35 and 80:20. Swine waste without cassava meal was treated as the control fermentation.
Fermentation o f cassava tuber meal with swine waste
295
In order to obtain about 40% moisture content in all the mixtures, water was added to the waste for the first mixture, and the waste for the last two mixtures was sun-dried. Although drying the waste will add cost, it was deemed necessary to dry the swine waste to avoid undesirable butyric acid fermentations that occur with fermenting waste mixtures of 40% moisture or more. No drying or addition of water to the waste was required to achieve 40% moisture with the 53:47 mixture. Six 1-kg portions of each mixture were packed in doubled polyethylene bags (1 mil thick), which were pressed to expel the air and then individually sealed. The polyethylene bags were stored at 28 + 2°C to promote fermentation of the mixtures. After a fermentation period of 42 days, the polyethylene bags were opened and the appearance and odor of the ensilage were evaluated. Three replicate samples from the central part of each bag were taken and frozen for later analysis. Total nitrogen, dry matter, ether extract and ash were determined by AOAC procedures (1980). Crude fiber was determined by the procedure of Van de Kamer and Van Ginkel (1952). Water-soluble carbohydrate (WSC) content was estimated according to the method of Dubois e t al. (1956) as adapted to corn plants by Johnson et al. (1966). Lactic acid content was determined by the method of Barker & Summerson (1941), and lactic acid buffering capacity of the waste/ICTM mixtures was measured by the procedure of McDonald & Henderson (1962). Levels of VFA were determined by the method of Kroman et al. (1967). Sample preparation for ammonia-nitrogen and titratable acidity determinations was according to the procedure of Jakhmola et aL (1984). The analyses for ammonia-nitrogen and titratable acidity were conducted according to APHA (1980). Sample preparation for pH determination (electrometrically) was according to the procedure of Weiner (1977). The data were subjected to analysis of variance including a linear effect for increasing levels of swine waste (orthogonal polynomial, Steel & Torrie, 1980).
RESULTS A N D DISCUSSION The proximal composition of the integral cassava tuber meal is presented in Table 1. The tuber meal was low in crude protein, fiber, fat and ash content, but high in nitrogen-free extract. The composition was in agreement with values reported by Gerpacio (1979), Khajarern et al. (1977) and Ravindran et al. (1982). However, the swine waste was high in crude protein and relatively low in nitrogen-free extract as previously reported by Kornegay et al. (1977). Mixtures of the two substrates potentially should provide an alternative, low-cost nutrient feed source.
G. Iniguez Covarrubias et al.
296
TABLE 1 Proximal Composition of the Dried Integral Cassava Tuber Meal
AnaO'ses (dry basis) Moisture Crude protein (N × 6'25) Crude fiber Ash Ether extract Nitrogen-free extract a a
% 4-54 2-20 4"59 2.17 0.56 90.48
The nitrogen-free extract was calculated by difference.
Studies conducted by Caswell et aL (1975) with broiler chicken waste and Knight et al. (1977) with beef cattle waste showed that the optimum moisture level for lactic fermentation of these wastes ensiled with conventional feed ingredients is 40%. Mixtures of swine waste and ICTM were prepared to have a moisture content of approximately 40%. The pH of the mixtures before ensiling ranged from 6.3 to 6"6 and the water-soluble carbohydrate levels ranged from 1"9% (dry basis) for the swine waste alone to 11"3% for the highest proportion of tuber meal blended with swine waste (Table 2). After the mixtures were ensiled for 42 days at 28°C, acid was produced in all mixtures including the swine waste ensiled alone. The swine waste without tuber meal achieved a pH of 5.7 after fermentation. Mixtures of tuber meal and waste had lower pH values after ensiling. The mixture containing the highest level of tuber meal (42 parts) achieved the lowest pH (4.2). These results indicate that the addition of tuber meal to swine waste improved the fermentation characteristics of the waste. The biological production of acid is associated with the fermentation of carbohydrates. The data in Table 2 show a direct relationship between the level of WSC in the mixtures with acid development as measured by pH. Lactic acid was produced in all the mixtures but reached highest levels in mixtures containing 20-35 parts of tuber meal. Levels of volatile fatty acids increased with increasing proportions of swine waste in the mixtures. Higher ratios of lactic acid to VFA, which are indicative of good quality silage, were demonstrated in mixtures containing the higher levels of tuber meal. Acid production in the ensiled mixtures was directly related to the level of cassava tuber meal in the mixtures. When the mixtures contained 47 parts or more of cassava meal, acid development as revealed by pH was 4.5 or lower, which is sufficient to preserve-the mixtures and to eliminate most enteric pathogens that might be encountered in the swine waste (Weiner, 1984).
297
Fermentation o f cassava tuber meal with swine waste TABLE 2
Fermentation Characteristics of Varied Levelsof Swine Waste and Integral Cassava Tuber Meal on pH, Water-Soluble Carbohydrates, Volatile Fatty Acids and Lactic Acid Analyses~
Proportions o f swine waste and integral cassava tuber meal (wet basis) 42:58
53:47
65:35
80:20
100
SEM
Before ensiled: Moisture (%) pH WSCb (%) Volatile fatty acids (%) Lactic acid (%) Ratio lactic acid to VFA
40-77 6'32 11.30 0"73 1'09 1.49
37-53 6.64 9-90 1'42 1'35 0.95
38.77 6"52 6"93 2"24 1.54 0.69
39-51 6"58 5-83 3'43 1'94 0.57
39.10 6.55 1.85 4.93 2.10 0.42
0.29 0-01 0.19 0-30 0"10 0.08
After ensiled (42 days): pHc WSCc (%) Volatile fatty acidsc (%) Lactic acidc (%) Ratio lactic acid to VFAc
4.15 32.47 1.54 6'12 3'97
4.48 29"33 2-38 6"57 2'76
4.62 21.62 3.41 8"08 2'37
4.93 13.51 4-88 7"98 1'64
5-68 1-58 5.86 3'58 1.64
0-03 0.31 0-03 0"15 0"11
a Each value represents the mean of three samples. All analysesexcept moisture and pH are expressed on a dry basis. b Water-soluble carbohydrates. c Linear effect of treatment (P < 0.01). On a wet basis, the cassava meal contained about 20% WSC and the swine waste about 1.9%. To achieve a pH of 4.5 or less in the ensiled mixtures, about 10% WSC was required in the swine waste/ICTM mixture. Therefore, the data in Table 2 indicate that about 47 parts of cassava tuber meal are required to achieve a pH of 4.5 or less in the ensiled mixture. The WSC level of the fermented samples increased after the ensilage period, it being higher for those samples with higher cassava tuber meal content. This could be due to the activity of extracellular amylolytic enzymes produced by starchhydrolyzing L a c t o b a c i l l u s . N a k a m u r a & Crowell (1979) isolated several starch-hydrolysing L a c t o b a c i l l u s strains from swine waste-corn fermentation. Langston e t al. (1962) reported that m a n y silage organisms hydrolyse and ferment starch, especially high acid-producing lactobacilli. The lactic acid-buffer capacity (LBC) of the mixtures before fermentation increased with increasing proportions of swine waste in the mixtures (Table 3). Similar results were reported by K a m a r a e t al. (1984) for ensiled cattle waste. It is clear that if animal waste intended for silage has a high buffering capacity, more acid must be produced during fermentation to achieve a low pH to insure the microbial safety of the product. McCaskey & W a n g (1985)
298
G. Iniguez Covarrubias et al. TABLE 3
Lactic Acid BufferCapacity, Titratable Acidity and Ammonia-Nitrogen Levels of Waste and Integral Cassava Tuber Meal Mixtures Analyses~
Before ensiled: Lactic buffer capacity (mg lactic acid/g DM) After ensiled: Titratable acidityb'c (mM acid/100g DM) Ammonia-nitrogen c (% DM) (% Total-N)
Proportions of swine waste and integral cassava tuber meal (wet basis) 42:58
53:47
65:35
80:20
100
SEM
42.22
78-82
112-60
150"15
242"09
0"60
30.62
36.52
44-18
40.77
13-40
0.30
0.08 11.28
0.21 15-69
0.37 17.05
0.65 19.76
1-02 23.68
0.09
a Each value represents the mean of three samples. b Titratable acidity is expressed as mM of lactic acid equivalent in 100g dry matter of mixtures. The samples were titrated with 0"05N NaOH to pH 7. c Linear effect of treatment (P < 0.01). reported a higher LBC for poultry litter silage than for bovine manure silage, and corn silage had the lowest buffering capacity. Animal wastes that have high crude protein levels tend to also have a high acid-buffering capacity. Drying the swine waste to achieve 40% moisture in the 65:35 and 80:20 (waste :meal) blends might have decreased the nitrogen content of these blends. Therefore, ammonia and crude protein contents o f these blends might be higher than reported in this study. Examination o f the ammonia-nitrogen data (Table 3) for the fermented mixtures indicates that swine waste at each level caused an increase in the proportion of ammonianitrogen. The degradation o f nitrogenous substances in the swine waste is the obvious source of the ammonia. H a r m o n et al. (1975) reported that ammonia-nitrogen content o f fermented silages tended to increase with increasing proportions o f broiler litter in the silages. High-quality silages contain high levels of lactic acid relative to volatile acids, a low p H (Langston et al., 1962) and a relatively low level of ammonia-nitrogen, generally less than 15°/0 of the total nitrogen (Nillison, 1956). Although microbiological analyses were not conducted on the ensiled mixtures, the ensiling process has been demonstrated to be an effective method of eliminating undesirable microorganisms. Coliform bacteria in bovine manure-blended rations were eliminated after the rations were ensiled I0 days and reached p H values of 4.7 and 4.5 (Knight et al., 1977).
Fermentation o f cassava tuber meal with swine waste
299
TABLE 4
Proximate Composition of SwineWaste and Integral Cassava Tuber Meal Mixtures After Fermentation Proportions o f swine waste and integral cassava tuber meal (wet basis)
Analyses (dry basis)
Moisture (%) Crude protein b (N × 6.25) (%) Crude fiberb (%) Ash b (%) Ether extract b (%) Nitrogen-free extract "'b (%)
42:58
53:47
65:35
80:20
100
SEM
41.89 4'37 6.00 3.01 0.82 85.80
40.76 8-55 7-93 6-04 2.73 74-75
41.87 13.57 8"67 9.87 4.45 63.44
41-79 20-56 11-64 13"64 6.80 44"05
38.73 26.81 13.72 18"18 11.13 30'16
0'12 0.43 0-29 0'25 0.19 0'75
" The nitrogen-free extract was calculated by difference.
b Linear effectof treatment (P < 0.01).
Salmonella typhimurium, Escherichia coli and species of Mycobacterium were eliminated from bovine manure silage when the pH decreased to 4.5 or less (McCaskey & Shehane, 1980; McCaskey & Wang, 1985). Fermentation of bovine manure-feed mixtures to a pH of about 4"5 or less will eliminate Brucella abortus if the organism is present in manure (McCaskey, 1985). In this study, mixtures of swine waste and tuber meal that contained 47 parts or more tuber meal had pH values of 4-5 or less after the ensiling process (Table 2). The proximate composition of the ensiled swine waste and tuber meal mixtures is shown in Table 4. The crude protein levels of the mixtures ranged from 4.4% to 20-56% (dry basis) and were directly related to the level of swine waste in the ensiled mixtures. Similar trends were observed for crude fiber, ash and ether extract. The ensiled mixture (53 parts waste to 47 parts tuber meal) that achieved just under pH 4-5 contained 8-6% crude protein, 7.9% crude fiber, 6% ash and 2-7% ether extract. This mixture represents the highest nutrient level that should be considered safe from zoonotic diseases. This study demonstrated that ICTM can be used as a carbohydrate source to improve the fermentation of swine waste. At a ratio of 53:47 wet basis (swine waste to cassava tuber meal), the mixture with 40% moisture achieved pH 4.5 which has been demonstrated with ensiled animal waste mixtures to be sufficient acidity to preserve the mixture and eliminate potential pathogens such as Salmonella (McCaskey et aL, 1985). Swine waste treated and preserved by fermentation with cassava tuber meal might serve as a process to convert these available resources into a low-cost, alternate feed source.
300
G. Iniguez Covarrubias et al. ACKNOWLEDGEMENTS
The authors express thanks to Consejo del Sistema Nacional de Educacion Tecnologica (COSNET, Mexico) for financial support o f this study, and to the faculty at A u b u r n University who edited the manuscript. Special thanks is given to Sarah H u n t who typed the manuscript.
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