Methane Digester Effluent as a Feedstuff for Layers1

Methane Digester Effluent as a Feedstuff for Layers1

Methane Digester Effluent as a Feedstuff for Layers1 J. M. CALDWELL, J. J. LYONS, and J. M. VANDEPOPULIERE Animal Sciences Department, University of M...

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Methane Digester Effluent as a Feedstuff for Layers1 J. M. CALDWELL, J. J. LYONS, and J. M. VANDEPOPULIERE Animal Sciences Department, University of Missouri, Columbia, Missouri 65211 (Received for publication January 2, 1985


Due to high energy costs, farmers are searching for alternate fuel sources to power equipment. Encroaching urban sprawl brings greater population pressures, and producers face more stringent regulations on sanitation and manure removal. As an energy converter, the methane digester could help solve some of these dilemmas. An anaerobic digester produces two products from the digestion of animal excreta, methane gas and a digester effluent. Methane digester effluent (MDE) containing approximately 98% moisture is a source of amino acids, ammonia nitrogen, energy, and minerals (Iannotti et al, 1979). Schmid and Upper (1969) observed digester effluent to have a pH of 7 with volatile fatty acids content ranging from 15,000 to 20,000 mg/liter. Consumption of wastes by animals has long been recognized as a source of nutrients. The advantage of direct incorporation of effluent into livestock diets is better utilization of the


Contribution from the Missouri Agricultural Experiment Station. Journal Series Number 9894.

effluent nutrients, particularly nitrogen (Hashimoto et al, 1978). Because of crude protein content and total amino acid concentration, Hashimoto and co-workers indicated that the effluent biomass was more valuable than the methane produced. Developing an application for MDE could reduce waste disposal problems encountered in intensive animal production; however the composition of the effluent must be determined before its feeding value can be judged (Iannotti et al, 1979). Smith et al. (1979) cited cultural stigma related to excreta, legislation and regulations which prohibit usage of sewage products in feed, and lack of technology to develop quality-controlled products as constraints to its use. They concluded that recycling of sewage solids would result if valid assessments indicated that usage would provide benefits which substantially outweigh costs and risks. Because the current costs of moisture removal using drying or centrifugation are prohibitive for this byproduct, it would be desirable to use it as a feedstuff in its natural, wet state. Considering the preceding factors, MDE was evaluated as a nutrient source in caged layer diets.


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ABSTRACT Methane digester effluent (MDE) from a full-scale digester (FD) was studied as a potential wet feedstuff for caged layers. Hens fed corn-soybean meal diets meeting National Research Council (NRC, 1977) nutrient requirements and containing up to .5% MDE, dry matter (DM) basis, showed no significant difference in hen-day egg production when compared with controls. Higher MDE levels (1.0 to 2.6%) produced a significant reduction in egg production. Egg weight and specific gravity were not affected by level of MDE. Haugh unit was adversely affected only in eggs laid by hens fed the highest level of MDE. True metabolizable energy (TME) and nitrogen corrected true metabolizable energy (TME n ) values of MDE samples from two types of digesters, pilot (PD) and full-scale were determined. Dry matter content was 2.92 and 1.58% for PD and FD, respectively. Mean gross energy values were 3502 and 3792 kcal/kg, and mean TME values were 1076 and 692 kcal/kg for PD and FD, respectively (dry matter basis). Both MDE samples had high gross energy values but comparatively low TME values, indicating that a large part of the nutrients in MDE were not digestible. The TME n values were 936 and 531 kcal/kg for PD and FD, respectively. Based on this study, .5% full-scale MDE (DM basis) is suggested as the maximum level that should be used in a caged layer diet. (Key words: methane digester effluent, egg production, egg quality, true metabolizable energy, digestibility) 1986 Poultry Science 65:147-152



Weeks 8, 12, and 16. Duncan's new multiple range tests were conducted for all parameters measured (Snedecor and Cochran, 1980). Egg Taste Panel. A triangle taste panel was conducted with hard-cooked eggs produced by hens fed the 0, .5, 1.6, and 2.6% MDE diets. Eggs were collected and refrigerated for 1 day and for 3 weeks prior to preparation. Eggs were prepared as follows: One cup of water was used for every egg to be hard-cooked. Tap water was placed in large 2-quart cooking pans and brought to a boil. When the water began to boil, the eggs were introduced with a large metal spoon. The water was maintained at 90 ± 2 C for 20 min, utilizing probe thermometers and adjusting the heating element manually. After 20 min, the hot water was poured off and the eggs were placed in a cold tap water stream for 5 min. After cooking, the eggs were stored in a refrigerator. Peeled and quartered egg samples were placed in small paper cups and evaluated by a panel of 39 untrained judges as to which two egg quarters were alike. Panelists rinsed their mouth with water before tasting each sample. Red lights were used for illumination to minimize color discrimination. The results were subjected to a Chi-square test to determine significance (P<.05) (Snedecor and Cochran, 1980). True Metabolizable Energy Trials. Twentyfour Single Comb White Leghorn roosters were housed in stair-step wire cages. Feathers and filoplumes around the cloaca were clipped to minimize contamination on the collection trays. All birds were weighed and sorted according to body weight. Plywood trays, 2.5 cm deep, 30.5 cm wide, and 61 cm long, were

TABLE 1. Mineral composition of methane digester effluent1'2

(%) p Ca K Na Mg Fe Zn Mn Cu

2.90 4.80 4.00 2.20 1.20 .20 .10 .05 .02


Calculated from Iannotti et al, 1979.


Dry matter basis.

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Caged Layer Feeding Trials. Based on plans and operating conditions for an energy selfsufficient, confinement pork production facility (Fischer et al, 1981), a 140 cubic meter, insulated, stave, full-scale silo digester was developed. Manure from a swine confinement unit was used to charge the methane digester with a loading rate of ca. 4 kg of volatile solids (VS)/m3. The effluent from this digester was used as an ingredient in caged laying hen diets. The MDE nutrient values were obtained from Iannotti et al, 1979 (Table 1). Six diets were formulated utilizing increasing levels of MDE 0, .5, 1.0, 1.6, 2.1, and 2.6% on a dry matter basis (Table 2). The control was a corn-soybean meal diet meeting NRC requirements for laying hens (NRC, 1977). Twelve-hundred H & N Pfizer, day-old pullets were obtained from a commercial hatchery. The chicks were vaccinated for Marek's disease at the hatchery and beaktrimmed at 14 days of age. The chicks were fed a chick prestarter for 2 weeks followed by the chick starter until 6 weeks of age. The chick grower was fed from 6 weeks of age until they were moved into the cage layer facility at 20 weeks of age. The unit consisted of two rooms each containing two banks of 120 wire cages in a stair-step arrangement. The cages were arranged in groups of five, each group sharing a common feed trough. Two pullets were placed in each cage for a total of 960 pullets housed. They were then fed a pre-experimental layer diet until 26 weeks of age. The 960 pullets were started on the MDE diets at 26 weeks of age. The basic design of the experiment was a 16-week randomized complete block with repeated measurements, producing a splitplot in time. The MDE was mixed with dry ingredients in a batch mixer weekly. Aflaban (Monsanto Chemical Co., St. Louis, Mo.) was added at a level of .05% to the diets containing MDE. As the percent MDE increased in the diets, they became noticeably wetter, and it was necessary to store the diets in plastic barrels. Feed not used immediately was stored at 7 C. Hens were fed daily and troughs of those fed the wet diets were cleaned weekly or more often as needed. Feed consumption in grams and hen-day egg production percentage were recorded weekly. Egg quality parameters such as egg weight, specific gravity, and Haugh units were determined on eggs from all hens the last day of



TABLE 2. Layer diets with graded levels of methane digester effluent1 Diet Ingredient





69.269 3.831

69.794 2.558

70.275 1.286




1.383 14.208 3.543 7.389

1.370 14.847 3.106 7.038 .500 .003 .270 .050 .025 .256 .183 100.000

1.377 15.473 2.709 6.669 1.000

1.340 16.168 2.310 6.565 1.600

1.346 14.068 3.854 6.155 2.100

.047 1.353 12.087 5.320 5.745 2.600

.271 .050

.273 .050

.274 .050

.275 .050

.514 .376 100.000

.490 .333 100.000

.474 .297 100.000

.448 .252 100.000

.009 .268 .050 .050 100.000


Calculated to contain 3.25% Ca and .5% P.


Dry matter basis.

'Provided per kilogram of diet: vitamin A, 8818 USP; vitamin D 3 , 3307 ICU; vitamin E, 9.5 IU; vitamin B n , .0088 mg; riboflavin, 5.5 mg; niacin, 55 mg; D-pantothenic acid, 15.45 mg; menadione, .75 mg; folic acid, 1.1 mg; pyridoxine, 1.1 mg; thiamine, .55 mg; Ethoxyquin (Monsanto Chemical Co., St. Louis, MO), 55.1 mg. "Contained (g/kg): manganese, 244; iron, 80; copper, 8; cobalt, 2.6; iodine, 4; zinc, 200; calcium, 2.5. 'Contained (g/kg): M n S 0 4 - H 2 0 67.8; ground limestone, 932.2. 'Contained (g/kg): ZnO, 27.5; ground limestone, 972.5.

covered with 914 Reynolds (Reynolds Metals Co., Richmond, VA) film and used for excreta collection. Eight true metabolizable energy (TME) trials were conducted according to the method of Sibbald (1983). Nine roosters were used per trial; three for endogenous measurements, three were precision-fed MDE from a full-scale digester (FD), and three from a pilot digester (PD). Dry matter content of both types of MDE was determined by drying samples in a 95-C forced-air oven for 24 hr. Mean TME values were calculated for both types of MDE and standard deviations derived. A Student's t-test was conducted for gross energy and TME values to determine significance (P<.05) (Snedecor and Cochran, 1980). Excreta energy values were corrected to zero nitrogen balance and nitrogen corrected TME values (TME n ) were calculated according to the equations derived by Sibbald (1983) and Sibbald and Morse (1983). Nitrogen Determination. The nitrogen contents of MDE samples were determined by the micro-Kjeldahl method Association of Official

Analytical Chemists (AOAC, 1975) modified as follows: The samples were digested for 30 min past the time of clear digestion, and a thin film of petroleum jelly was not placed on the rim of the flask after digestion and before distillation. The nitrogen content of the excreta samples was determined by the macro-Kjeldahl method (AOAC, 1975) Excreta samples of ca. .50 and .25 g were used for precision-fed and control roosters, respectively. For sample distillation, a Kjeltec system 1003 (Tecator AB, Hoganas, Sweden) was employed. Fiber and Ash Analyses. Neutral-detergent fiber (NDF) and acid-detergent fiber (ADF) were determined according to the procedure cited in Forage Fiber Analyses (1970). Hemicellulose content was calculated by subtracting ADF from NDF. The percent ash was determined for both MDE samples according to the method of AOAC (1975). RESULTS AND DISCUSSION

Body Weight Gain. As shown in Table 3, hens fed the .5, 1.6, and 2.6% MDE diets were not significantly different in body weight gain

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Ground corn Wheat middlings Stabilized fat Dehydrated alfalfa meal, 17 Soybean meal, 44 Meat and bone meal, 50 Ground limestone Methane digester effluent2 DL-Methionine Salt, NaCl Vitamin premix 3 Trace mineral premix 4 Manganese premix 5 Zinc premix 6 Total




CALDWELL ET AL. TABLE 3. Production performance of hens fed methane digester effluent


<% M D E ) 1

(% DM) 1




90.0 70.2 59.2 50.2 43.9 38.8

25.4C 52.4ab 70.1a 40.0b 20.4C 30.6bc

88.0a 87.4a 82.1° 73.4C 7 3.4 C 70.9C

.5 1.0 1.6 2.1 2.6


Hen-day production

Feed consumption, DM /

Feed consumption, w e t basis


, j

94.1d 104.0b 108.0a 99.5C 98.6C 96.9cd

Feed efficiency (g egg/g feed DM)

104.5f 148.le 182.5d 198.0C 224.7b 249.8a

.52a .46b .42b .41c .41c .41c

Column means with different letters are significantly different (P<.05). MDE = Methane digester effluent, DM = dry matter.

but gained less than hens fed the 1% MDE diet. Hens fed the control diet and the two highest levels of MDE, 2.1 and 2.6%, were not significantly different. Hens had comparable body weights when fed wet diets containing high levels of MDE. No loose droppings were observed with hens fed high levels of MDE. Apparently, the hens were able to adjust water intake to compensate for the moisture levels in the diets, probably by reducing water consumption. Hen-Day Production. Hens fed 0 and .5% MDE diets laid at comparable rates, exhibiting no significant difference. As the dietary dry matter decreased below 70%, hen-day production decreased (Table 3). The depressing effect of MDE on hen-day production appeared to level off in the diets containing 1.6 to 2.6% MDE. Even with Aflaban added as a mold inhibitor and the feed stored in a cooler, mold and fungal growth were observed in the diets containing MDE. The suppression in performance may be due in part to mold and fungal development. Dry Matter Consumption. Dry matter (DM) consumption varied; however, the highest was on the diet containing 1% MDE diet (Table 3). Even with increased levels of DM feed consumption, the higher MDE levels produced a decrease in hen-day production. The lowest levels of DM consumption were exhibited by the hens fed the control and the 2.6% MDE diets. This indicated that DM consumption was not adversely influenced by the moisture content of the diets. It appeared that the hens could adjust their wet-basis feed consumption to maintain DM intake comparable to, or

greater than, the control; however the feed efficiency was significantly better for the control (Table 3). The Relationship of Dietary Methane Digester Effluent Level with Nutrient Intake. Protein and energy intake were evaluated (Table 4). On the MDE diets, the nutrients obtained from ingredients other than MDE should have been adequate to support production comparable to the control diet. Protein and energy intake were higher than for the control diet with the exception of the protein intake of the hens consuming the 2.6% MDE diet. However, hen-day production was significantly lower on diets with higher levels of MDE (1, 1.6, 2.1, and 2.6%). This indicates that the nutrients were rendered less available, or conditions developed that suppressed egg

TABLE 4. Daily nutrient intake of protein and energy excluding MDE1 co ntribution Protein, excluding MDE

Energy, excluding MDE

(% MDE)



14.1 15.5 16.0 14.7 14.5 14.0

(kcal ME/ hen) 268.2 296.4 307.7 284.1 281.5 276.7

.5 1.0 1.6 2.1 2.6 1

MDE = Methane digester effluent.

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Body weight



TABLE 5. Mean nutrient values of methane digester effluent samples from two sources Full scale digester Gross energy, kcal/kg 2 TME, kcal/kg 2 TME n , kcal/kg 2 N, % CP, % NDF, % cell wall ADF, % lignocellulose Hemicellulose,3 % Ash, %

3791.8a ± 31.2' 691.6b ± 113.6 507.4b ± 74.6 .02 3.45b ± .12 21.56° ± 39.4a ± .9 1.4 31.0a ±




a ' b Row means with different letter are significantly different (P<.05). 1

Standard error of the mean.


Dry matter basis.


Determined by subtracting ADF from NDF, no standard error determined.

Pilot digester 3502.5b 1067.3a 911.6a 3.77a 23.57a 17.9b 7.6b 10.3

± 24.7 ± 104.9 ± 58.9 ± .04 ± .26 + .3 ± .3 ±


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Sibbald and Morse (1983) recommended correcting the excreta energy values to zero nitrogen balance to reduce variation and error mean squares. The TME and TME n values were evaluated for the full scale digester and for the pilot digester (Table 5). A realized power of the F-test calculation following the method of Tiku (1967) indicated that small differences can be detected with greater power with TME n than with TME. One appreciable source of error in the bioassay was contamination of excreta by scale and feathers. The development of a suitable collection device should be encouraged to eliminate contamination. Sibbald (1983) reported the successful use of a self-adhesive, plastic colostomy bag. Crude Protein. As shown in Table 5, crude protein percentages for FD and PD were substantially higher than that observed by Iannotti et al. (1979). However, Iannotti and co-workers were careful to exclude ammonia nitrogen from their crude protein value. They reported that ca. 75% of MDE nitrogen was ammonia nitrogen due to its volatile nature. The nitrogen content calculated probably reflected crude protein available for poultry because of the inability of monogastrics to utilize nonprotein nitrogen (ammonia) sources to any great extent. Methane Digester Effluent Fiber Assays. The FD sample exhibited the highest fiber content; however, it contained a lower level of hemi-

production. This could include spoilage, the development of aflatoxins, or water intake associated with the wet feed consumption. Egg Quality Parameters. Egg weight and specific gravity exhibited no significant differences among treatments. Although not significantly greater, the 2.6% MDE treatment exhibited the largest egg weight; however, Haugh unit measurements were significantly lower when compared to the other five treatments. An explanation for this difference in Haugh units is not apparent. Egg Taste Panels. There was no significant difference in the flavor of eggs produced on diets with and without MDE. At the levels fed, MDE did not affect the gross organoleptic properties of the egg. True Metabolizable Energy Trials. The MDE samples used in the TME studies contained dry matter levels of 2.92 and 1.58% for PD and FD, respectively. Differences between samples could be attributed to digester inputs. The PD inputs were more closely controlled, while the FD inputs were variable, containing not only manure but some wasted feed and bedding. The PD was charged with manure from hogs fed a 14% corn-soybean meal diet and raised on a concrete and wood floor, avoiding straw and other bedding materials. The FD was charged with hog manure and beef cattle manure from a feedlot. As shown in Table 5, FD had a higher gross energy value but a lower TME value than PD suggesting a lower digestibility.



cellulose than the PD source (Table 5). This could be a partial explanation of the higher TMEof PD. The PD had a higher ash content than the FD (Table 5). Obviously the feed, bedding, and cattle manure of the FD were of a fibrous nature containing a low level of ash.


REFERENCES Association of Official Analytical Chemists, 1975. Official Methods of Analysis. 12th ed. Benjamin Franklin Station, Washington, DC. Fischer, J. R., N. F. Meador, C. D. Fulhage, and F. D. Harris, 1981. Energy-self-sufficient swine production system — a model. Trans, of the ASAE 24:1264-1268, 1272. Forage Fiber Analyses, 1970. Agric. Handbook No. 379. Agric. Res. Service, USDA. Jacket No. 387-598. US Gov. Printing Office, Washington DC. 20302. Hashimoto, A. G., R. L. Prior, and Y. R. Chen, 1978.

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The authors gratefully acknowledge Ruth Baldwin, Gary Krause, and J. R. Fischer for their expertise and technical assistance.

Methane and biomass production systems for beef cattle manure. Great Plains Seminar on Methane Production from Livestock Manure. Liberal, KS. lannotti, E. L, J. H. Porter, J. R. Fischer, and D. M. Sievers, 1979. Changes in swine manure during anaerobic digestion. Dev. Ind. Microbiol. 20: 519-529. National Research Council, 1977. Pages 2 9 - 3 0 in Nutrient requirements of poultry. 7th ed. Natl. Acad. Sci., Washington, DC. 20418. Schmid, L. A., and R. L. Lipper, 1969. Swine waste characterization and anaerobic digestion. Pages 50—57 in Proc. Agric. Waste Manage. Conf., Cornell Univ. Ithaca, NY. Sibbald, I. R., 1983. The TME system of feed evaluation. Anim. Res. Centre, Ottawa, Ontario, Canada. Sibbald, I. R., and P. M. Morse, 1983. Effects of the nitrogen correction and of feed intake on true metabolizable energy values. Poultry Sci. 62: 138--142. Smith, G. S., H. W. Kiesling, and E. E. Ray, 1979. Prospective usage of sewage solid as feed for cattle. Pages 190-200 in Proc. 8th Natl. Conf., Miami Beach, Fl. Snedecor, G. W., and W. G. Cochran, 1980. Statistical methods. 7th ed. Iowa State Univ. Press, Ames, IA. Tiku, M. L., 1967. Tables of the power of the F-test. J. Am. Statist. Assoc. 62:525-539.