PART IV (Contd.)

CHAPTER 18
SYSTEMS FOR THE INDIRECT RECYCLING BY USING ANIMAL AND MUNICIPAL WASTES AS A SUBSTRATE FOR PROTEIN PRODUCTION

by

C.C. Calvert

Feed Energy Conservation Laboratory
Animal Physiology and Genetics Institute
Agricultural Research Service
United States Department of Agriculture
Beltsville, Maryland 20705

Resumen

Los millones de toneladas de desperdicios animales y municipales que se recojen y eliminan diariamente en todo el mundo representan un recurso potencialmente valioso para su transformación en alimentos para el ganado y las aves.

Actualmente se están estudiando atentamente estos desperdicios, porque ha aumentado la demando de proteínas vegetales para la alimentación humana y se está considerando el potencial de sistemas nuevos y antiguos para transformar los desperdicios animales y municipales en alimentos aceptables para los animales. En el presente informe se hace una reseña de los diversos sistemas de utilización indirecta de los desperdicios animales y municipales, mediante la transformación de los nutrientes que contienen en proteínas idóneas para la alimentación de los animales. Se ha referencia al empleo de organismos unicelulares e invertebrados, incluso algas, levaduras, hongos, cultivos mixtos de bacterias, larvas de mosca doméstica y lombrices de tierra, a partir de desperdicios.

La investigación mediante cultivo en estanque de algas unicelulares revela que este sistema permite producir proteínas de alta calidad (48–50 por ciento de proteína total), a partir de desperdicios, con rendimientos de 30–40 toneladas de algas secas/acre de superficie de estanque, al año. La evaluación nutritiva de las algas secas revela que éstas se pueden usar, con buenos resultados, como fuente de proteínas, en alimentos para animales.

Las larvas de mosca doméstica y las lombrices de tierra también dieron buenos resultados en la separación de las proteínas que contienen los desechos animales. Las pupas y los ejemplares adultos de mosca doméstica, derivados de larvas, secos contienen 63 y 75 por ciento de proteína total respectivamente y resultaron equivalentes a la proteína de la soya, en ensayos de cría de pollitos. Las lombrices de tierra secas contienen 58 por ciento de proteína total, pero no se ha informado de ningún ensayo de alimentación.

Se necesita más información sobre el rendimiento, la producción y los costs, para evaluar plenamente el potencial económico de estos sistemas de producción de proteínas. Los costos pueden limitar o entorpecer su aplicación. Los cultivos mixtos de microrganismos, según el sistema de zanjas de oxidación, producen un material proteináceo que se le ha agregado a los alimentos para cerdos y vacunos. Antes de poder usar estos materiales extensivamente, es preciso determinar su valor nutritivo y la cantidad que se le puede agregar, sin peligro, a los alimentos. Se están investigando otros sistemas potencialmente útiles de utilización de desechos animales como substratos; es posible que algunos den buenos resultados y permitan producir proteínas con diversos substratos que no sean desechos animales y municipales. Su potencial de utilización con desechos animales y municipales es real, pero hay que hacer investigaciones más extensivas en esta área.

18.1 Introduction

The millions of kilograms of nitrogen collected and disposed of each day in animal manure and municipal wastes represent a valuable reservoir of nitrogen potentially available for conversion to protein for livestock and poultry feed. Traditionally this nitrogen has been applied to land, where some of it is recycled into plant protein. However, these so-called waste materials are now coming under close scrutiny because of increased demand for plant proteins for human food; as a result, new and old systems are now being considered for their potential for converting animal and municipal wastes into acceptable animal feedstuffs.

This review concerns the various systems using animal waste nitrogen in the indirect production of protein suitable for livestock and poultry feed. In some systems, wastes from sources other than livestock and poultry have been used to produce protein materials, and these will be discussed if they can be used with animal waste.

The general subjects that will be reviewed will be the use, for protein production from animal wastes, of both unicellular organisms and invertebrates, including algae, yeasts, bacteria, mixed cultures of micro-organisms, fungi, molds, housefly larvae, earthworms, and miscellaneous invertebrates. The technical aspects of the various systems used, the nutritional value of the product, and the potential practicability of the proposed systems for protein production will be discussed.

18.2 Micro-organisms Utilized in the Production of Protein from Wastes

18.2.1 Algae

18.2.1.1 Production Systems

The large-scale culture of numerous algal species and their use as feed sources began in the early 1950s. As pointed out in reviews by Krauss (1962) and Priestley (1976), the total capacity of mass culture systems increased almost logarithmically up to about 1968. The total capacity in 1968 (Oswald and Golueke, 1968) was estimated at about 10⁷ litres. Whether the projected capacity of 10¹⁰ litres has been achieved in 1976 is difficult to determine, but if interest in algal culture continues as proposed by Priestley and others, by 1989 a total volume of 10¹⁵ litres could supply enough feed for livestock to cover the world's projected animal protein needs.

Much of the early research on the use of algae deals with the treatment of sewage effluents for water clarification, in which algae served as a source of oxygen for aerobic digestion of organic materials. Algal protein was a byproduct of these systems. The early experiments of Ludwig et al. (1950, 1951), Gotaas et al. (1951), and Oswald et al. (1953a, b) established many of the criteria for loading rates of lagoons, photosynthetic requirements, growth characteristics, and other technical parameters necessary for the use of algae in the treatment of sewage effluents.

For a comprehensive discussion of algae production in systems for other than animal wastes, the following reviews are useful; Krauss (1962), Litchfield (1968), Dabbah (1970), Lipinsky and Litchfield (1970), Reed and Peppler (1973), and Priestley (1976).

Currently, two systems in which algae are used for the treatment of animal wastes have been investigated on a pilot-plant scale. The first of these was described by Dugan et al., (1969, 1971), and a schematic diagram of this operation is shown in Figure 18.1. Manure from a caged layer operation is flushed into a sedimentation tank, supernatant from this tank is pumped directly to an algae pond, and the sediment is pumped to an anaerobic digester for methane generation. The methane generated is used as an energy source to heat the digesta, any excess being stored for further use within the system. Effluent from the anaerobic digester is pumped into the algae pond. After algae separation, water is recycled in the system.

In the operating pilot plant, the following observations were made: 1) depth: not greater than 30.5 cm; 2) pond area needed: approximately 0.18 m²/bird; 3) amount of water needed to establish the overall system: 56.8 litre/bird; 4) gas production for the system: about 0.75 m³/kg of volatile solids introduced, methane constituting about 50 to 60% of the gas produced; 5) potential algal yield: 11 to 15 metric tons DM/ha/year; and 6) operating cost at the time: about 2 cents per dozen eggs produced.

Figure 18.2 shows a schematic diagram of a system currently being tested at Oregon State University by Miner et al. (1975). This system is similar in concept to that designed by Dugan except that it uses swine wastes. The principal difference between the two systems is the rotating flighted cylinder used for solid/liquid separation. This system is designed for 50 finishing swine, furnishing about 16 kg of volatile solids per day. Twelve algae basins with a surface area of 2 m² each will be used with this system. Because of the geographical location, a heat exchanger system is being provided for each basin. Some preliminary studies on algae growth have been conducted over a period of about 1 year, and projected yields were as follows: 1) mean dry matter: 121.5 tons/ha/year; and 2) crude protein, 55 tons/ha/year. The algal pond system reduced the total nitrogen content of swine waste by 90%, but algae accounted for only about 20 to 40% of the nitrogen loss.

FIGURE 18.1 Schematic Diagram for Algae Production from Poultry Waste. (From Dugan et al., 1969).

As reported by Lipinsky and Litchfield (1974) and Priestley (1976), a number of large-scale algae production units utilize municipal and industrial wastes as substrates for protein production. Because the above authors have extensively reviewed these systems, they will not be discussed here except to indicate that they have operated with varying degrees of success. However, if fluctuations in the source of waste products could be reduced and the use of algae produced by these systems is approved by the regulatory agencies, enthusiasm for the development of protein production systems might well increase.

18.2.1.2 Nutritional Value

The nutritional value of algae produced on a variety of substrates has been determined for both ruminant and nonruminant animals, including man, (Because this review is concerned with livestock feeds, the use of algae for human food will not be discussed.) One of the first experiments on the use of algae for nonruminant animals was a chick-feeding trial conducted by Combs (1952). His results showed that dried Chlorella could supply some water-soluble vitamins and carotene but was inferior to soybean meal as a protein source. Methionine significantly improved chick growth when added to the algae-containing diets, but growth did not equal that obtained when these ingredients were replaced in the diet by soybean meal.

Hundley et al, (1956) reported that supplementation of Scenedesmus obliquus and Chlorella pyrenoidosa with lysine resulted in increased weight gains in rats, and Leveille et al. (1962) reported a similar response with the addition of methionine to Ch. pyrenoidosc. Cook et al. (1963) observed that the growth rate of rats was improved by cooking the algae.

Although extensive nutritional studies have been conducted on algae produced in a variety of systems, in the two examples of algal systems designed for use with animal wastes nutritional evaluations of algae have been limited. Apparently, no nutritional trials have been conducted with algae produced in the system described by Dugan et al. (1969). However, Miner et al. (1975) reported a study in which the average daily gains, intake, and protein efficiency ratios (PER) of Chlorella vulgarii grown on swine waste were determined. In that study (Table 18.1), the average daily gain and PER of centrifuged algae were not different from those of cottonseed meal or dried brewers' yeast. Much more information is needed to determine the nutritional value of Chlorella produced in this manner, but these results certainly suggest that algal protein produced from swine waste is comparable with that from other sources of algae and from some conventional protein sources.

FIGURE 18.2 Schematic Diagram for Algae Production from Swine Waste. (From Miner et al., 1975).

As expected, algae are better utilized by ruminants than by monogastic animals. Hintz et al. (1966) conducted a study in which mixtures of algae Chlorella spp., Scenedesmus obliques, and S. quadricanda) were fed to sheep and cattle. The composition of this mixture, which was grown on sewage effluent, is shown in Table 18.2. The ration was pelleted to avoid sorting and refusal of the algae. The dry matter and crude protein digestibilities (Table 18.3) were similar for cattle and sheep, but the digestibility of the algal carbohydrates was lower than might have been expected, possibly because this fraction contained a large percentage of algae cell walls, resistant to digestion by cattle and sheep, or because of the small particle size of the algal material and the predictably rapid ruminal passage of this material. Because of the high protein digestibility and the carotene and mineral content, the authors concluded that dried algae were a potentially valuable feed for ruminant livestock.

Source: Miner et al., 1975

^a Values 1 standard error.
^b Micrograms per gram.

Source: Hintz et al., 1966

The microscopic single-cell forms of algae have the potential for being a useful and profitable means of converting nitrogen in animal and municipal wastes to protein for livestock feed. As described by Priestley (1976), the advantages of algal production systems may be summarized as follows: 1) waste products used in the production of algae require little or no processing before use; 2) algae have essentially the normal amino acid composition of single-cell protein (SCP) microbes, but with a substantially lower nucleic acid content; and 3) the capital investment for production systems required is lower than that for other SCP systems. Some of the problems encountered with algae production which could limit worldwide application are: 1) separation of the product from the culture media; 2) climatic and topographic limitations on pond function and location; 3) the large amounts of space required for algal ponds to process large quantities of wastes; and 4) high capital outlay to establish the systems. If adequate markets can be established for algae proteins, and the systems can be designed to operate on a year-round basis, it is possible that such systems could play an important role both in controlling animal waste problems and in producing an acceptable protein for livestock feed.

18.2.2. Yeasts

18.2.2.1. Production Systems

The potential for protein production by yeast compared with other means is phenomenal. Thaysen (1956) emphasized this point by comparing the protein production of a 454-kg beef animal, 454 kg of soybeans, and 454 kg of yeast. 454 kg of beef animal can provide about 454 g of protein/day; 454 kg soybeans over their growing season can provide about 36 kg of protein/day; but 454 kg of yeast can provide about 45 metric tons as protein/day.

Extensive efforts are being made to develop systems to produce yeast proteins from a variety of substrates. According to Lipinski and Litchfield (1974) and Shacklady (1974), two companies are producing yeasts grown on hydrocarbons on a commercial scale for the animal feed industry. A number of oil companies in Europe and the U.S. are in the process of developing their own systems, and in the near future a number of other sources of yeast protein from petroleum by products will probably be available to the animal feed industry. A discussion of the various systems for the production of yeasts on substrates other than animal and municipal wastes is not within the scope of this report; the reader should consult reviews by Dabbah (1970), Litchfield (1968), Lipinsky and Litchfield (1970), and Shacklady (1972, 1974) for more information on these processes.

Little research has been conducted on the use of animal and municipal wastes as substrates for yeast growth. According to reports by Singh and Anthony (1968) and Anthony (1969), yeast was grown on aerated, fluidized cattle manure, the fibre was hydrolyzed, the lignified fraction was discarded, and the solubilized and yeast-fermented fraction was concentrated for use as cattle feed. About 68.6% of the manure dry matter was recovered in the solubilized fraction, which was dried and fed to rats with less than satisfactory results. All rats failed to gain weight and developed diarrhea, which was attributed to the high mineral content of the material. Apparently, these investigations have not been developed further.

¹ Calculated by difference.
² Nonprotein, nonfat organic matter.

Source: Hintz et al., 1966

18.2.2.2 Nutritional Value

In the absence of any information on the nutritional value of yeast grown on animal or municipal wastes, the nutritional value of yeasts produced from other materials such as petroleum byproducts will be discussed. A number of reports have dealt with the safety and efficiency of yeasts as animal feeds and have been reviewed extensively in the references mentioned above. In addition, a report by Shacklady and Gatumel (1972) deals specifically with a product produced on alkanes by British Petroleum Proteins, Ltd., and now marketed as a protein supplement for livestock feed.¹ The general findings from these studies indicated that yeasts produced in this manner presented no safety hazard to livestock or humans. The net protein utilization (NPU) of these yeasts ranged from 50 to 60 with a biological value (BV) of 54 to 61. When supplemented with methionine, the NPU increased to 88 to 91 and BV to 91 to 96, comparable with values for dried milk or whole egg used in the same studies. In studies with swine and poultry, dietary levels of 7.5 to 15% of yeast proteins were equal in replacement value to fishmeal, soybean meal, or mixtures of the two in the diet.

Van Weerden et al. (1970), using the yeast in poultry rations, found its metabolizable energy--2550 kcal/kg-- to be between those of fishmeal and soybean meal and recommended that it could be added to chick diets at a level of 10%; weight gains were reduced slightly when it was substituted at 15% of the ration.

These results were generally confirmed by Waldroup et al (1971) with yeast produced by Gulf Research and Development Co. The results of this study are shown in Table 18.4.

Yeast substitution up to 15% of the diet resulted in good growth and feed utilizaation. When yeast comprised between 15 and 25% of the diet, the feed had to be pelleted for maximum growth and feed efficiency. When it comprised more than 15% of the diet, the feces from the chicks became sticky and tended to adhere to the wire-mesh floor of the cages or to encrust on litter. This type of feces could be a problem if similar levels were to be used under conditions of commercial production.

In a study with laying hens, Yoshida (1975) has shown that yeasts grown on n-paraffins are an excellent source of protein, energy, and phosphorus but are somewhat deficient in sulphur amino acids. No toxic factors were detected in this yeast.

The available information indicates that yeast can be grown on wastes to produce useable protein, particularly for poultry and swine. Extensive efforts have not been made to determine whether animal manure would be a suitable substrate, but there is reason to believe that such a system could be developed.

18.2.3 Bacteria and Mixed Cultures

In the existing methods of disposal, including composting, aerobic and anaerobic digestion, and land application, animal wastes are attacked by a variety of organisms; it would seem reasonable to look at the potential of a system in which controlled, single, or mixed bacterial cultures were used to digest animal waste and then harvested as protein.

Jones et al. (1972) have investigated the potential use of a high-protein fraction of feedlot manure unprocessed except by bacterial action on the surface of the feedlot. Their procedure has been to slurry feedlot manure with water, screen it, and either filtre or centrifuge the slurry. The centrifuge or filtre cake obtained represented 40% of the total weight of manure and about 70% of the total nitrogen. These fractions contained about 35% crude protein and had an amino acid composition that appeared superior to that of cereal grains and comparable with that of soybean meal.

Vetter (1972) reported on a study in which oxidation ditch liquid was pumped directly from the ditch into a feed wagon and mixed with a basal cattle ration. The analysis of the oxidation ditch liquid is shown in Table 18.5.

¹ Mention of a trade name, proprietary product, or specific equipment does not constitute a guarantee or warranty by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products that may be suitable.

¹ Means having the same superscript in the same column do not differ significantly (P < 0.05)

Source: Waldroup et al. 1971.

Depending on the method of analysis, the dry matter composition was 5.0 to 6.1%, and the crude protein content ranged from 24 to 48%. A fibre content of 34% and ash content of up to 18% would mean that only limited quantities could be fed to cattle. The in vitro digestibility of dry matter indicated that the material would be relatively well utilized by cattle. This utilization was also evident when the cellulose-lignin content (22%) was compared with that of dry matter (47%) for forages as reported by Anthony (1971).

Table 18.5 Percentage of Nutrient Composition of Feedlot Cattle Wastes Processed Through an Oxidation Ditch Unit (Dry Matter Basis)

¹ Equivalent to 25 to 50% of total nitrogen.

Source: Vetter, 1972

Results of feeding trials in which oxidation ditch material was used are presented in Table 18.6. They show that at the level of dry matter added, growth of cattle fed oxidation waste was equivalent to that of the controls. In trials 1 and 2, growth was somewhat better than that of the controls. Gross pathology did not reveal any problems from refeeding, and a trained taste panel could not detect any differences in flavour of meat due to waste feeding.

Harmon et al. (1972) reported that oxidation ditch liquids mixed from a swine operation averaged 7.9% protein, 3.4% dry matter, and 41.7% ash in samples collected over a 3-year period. The amino acid content of dried liquid mixed is shown in Table 18.7. According to these workers, lysine and tryptophan may be limiting amino acids in the swine waste.

Harmon and Day (1975) have also conducted studies in which oxidation ditch liquid has been fed to swine as the sole source of water. The oxidation ditch liquid is simply pumped into an open through in the pen on a regularly timed schedule. The results (Table 18.8) indicate that these swine performed as well as, or better than, those fed the regular source of water. Disease transmission or perpetuation in such a system and the potential for pathogen transfer to the consumer of animal products would seem to be a major concern if a system such as this were in general use. Also of concern to such a system is potential for concentrating various feed additive residues that might be used in swine rations. Certainly, long-term studies are needed, with specific emphasis on the possible concentration of feed additives and pathogens in the oxidation ditch liquid, in order to answer some of the questions on the practical use of unprocessed liquid waste from swine and beef cattle oxidation ditches.

Table 18.6 Processed Animal Waste Nutrients (PAWN) From an Oxidation Ditch System Added Directly to the Cattle Ration

¹ Average, 3.86; last 49 days, 6.12.

Source: Vetter, 1972

Table 18.7 Amino Acid Analyses of Oxidation Ditch Liquids (Summary of 13 Weekly Samples)¹

¹ Protein content was 49.56% of dry matter.

Source: Harmon et al., 1972.

¹ Each value is the average of six replicates of 10 pigs each receiving the treatments from 40 kg to market weight.

Source: Harmon and Day, 1975.

The production of bacterial protein on methanol - and petroleum-derived hydrocarbons has received considerable attention in the past few years. Maclennan et al. (1973), Imrie (1975), and Imrie and Righelato (1976) have reviewed these processes; the production for animal feeds of bacterial protein, particularly on a methanol substrate, would appear to be a viable process. A process using animal wastes has also been explored to a limited extent by the General Electric Co. in the U.S. Apparently this process, in which a pure culture of thermophilic bacteria was used, was developed to the pilot-plant stage but has been abandoned because of problems associated with maintaining the pure bacterial culture.

The nutritional value of bacterial protein has also been determined and, in most instances, compares favourably with that of other single-cell protein sources. Reports by Maclennan et al., (1973) and Waldroup and Payne (1974) indicated that growth of chicks was not adversely affected by bacterial proteins added at levels up to 10% of the ration. In both studies, the bacterium used was an adaptive strain of Pseudomonas. In Waldroup's study, increasing levels of bacterial protein to 15% of the ration resulted in decreased growth and feed efficiency of chicks. Substitution of bacteria into the diet was at the expense of soybean meal. In the experiments by Mclennan, levels up to 36% of the total protein did not adverself affect growth and feed efficiency, but in these experiments substitution was at the expense of fishmeal.

Agren et al (1974) observed some adverse effects on the health of rats when bacterial protein was used as the sole source of protein. The kind of bacteria used or the substrate on which they were produced was not specified. Yeast grown on the same substrate did not adversely affect rat performance or health.

In general, there is a potential for the use of bacteria grown on animal wastes as feed for livestock. At present, this potential has not been realized because of technological problems related to design of equipment and selection of appropriate strains of bacteria. The use of mixed cultures, as in oxidation ditches, has some potential and in some instances is ready for practical applications.

18.2.4 Fungi and Molds

This review will seek to determine the present or potential value of the large-scale culture of a variety of fungal species other than the common mushroom (Agaricus bisporus) as a foodstuff and as a means of disposal of animal wastes.

The submerged culture of fungal mycellum is the method that represents the greatest potential for protein production. The system is, as its name implies, the growth of the filamentous vegetative part of the fungus in an aerated, aqueous medium with available nutrients in either solution or suspension. The total solids content of the medium varies but, in general, would appear to be in the range of 3 to 6% for maximum growth of the mycelium. This technique was used in Europe during World War II to feed human populations and in the U.S. to produce antibiotics (Bunker, 1963, 1964). This experience led to the post-war interest in the potential for this method for the production of fungal mycelium for human consumption (Humfeld, 1948, 1952; Humfeld and Sugihara, 1949, 1952; Sugihara and Humfeld, 1954; and Szuecs, 1954, 1956, 1958). Others have pointed out that mushroom mycelium produced by submerged cultures might have potential for use as an animal feed (Gilbert and Robinson, 1957; Robinson and Davidson, 1959; Block, 1960).

As described in reviews by Falanghe (1967), Litchfield (1968), and Gray (1970), one of the real advantages of the submerged culture technique is the variety of substrates that can be used for the cultivation of fungal mycelium. They include such products as citrus-press water, malt extract, maize steep liquor, beet molasses, sulfite wastes, soybean whey, maize canning wastes, pumpkin canning wastes, cheese whey, and glucose; these are only some of the substrates that have been used, and the potential for the utilization of other waste materials is certainly great. The major considerations for a suitable substrate, according to Litchfield (1968), are the availability of assimilable carbohydrates and nitrogen sources and the costs, including those of collection, transportation, and pretreatment.

Would animal manures be a suitable substrate for mycelial growth? Studies of this nature are currently being conducted at the U.S.D.A. Northern Regional Research Laboratory at Peoria by Weiner and associates (personal communication), who are studying the growth of fungi on liquid fractions of cattle feedlot wastes. Some types of fungl appear to grow quite satisfactorily on the nutrient available in this kind of animal manure. Because the percentage of inorganic nitrogen in the nitrogen fraction of most animal manure is rather high (60 to 70%, according to a number of sources reviewed by Smith, 1973), these materials would seem to be an excellent source of nitrogen for mycelial growth. The available carbohydrate in most animal manures, however, might be limiting because in most manures it is in the form of complex polysaccharides from plant materials used as animal feeds. Some fungi are capable of utilizing these carbohydrates, but according to Litchfield (1968), these fungi act too slowly to make their use economically feasible. If a source of suitable waste carbohydrate was available, it certainly would seem feasible to mix this material with poultry or livestock manures to produce a medium that would support optimum growth of some type of fungal mycelium.

The protein content of 20 varieties of fungal mycelium has been reported by Litchfield in his review (1968). The values that he reports range from a low of 12.0% of dry matter for Penicillium griseofulvum to a high of 53.5% for C. Velutipes. A review by Gilbert and Robinson (1957) also gives an extensive evaluation of the nutritive contents of a wide range of fungi; in general, the protein content of many species would appear to be competitive with that of some of the common proteins now used in animal feeds.

A number of experiments with rats and mice and a few with humans have been conducted over the years, with varying results that were summarized by Litchfield (1968). These experiments suggest that the sulphur amino acids are limiting for rat growth, and that for maximum performance, fungal proteins would have to be supplemented with varying levels of these amino acids.

Toxicity is always a problem, particularly the production of fungi-toxins. This problem is being investigated, and toxicological studies would have to be conducted with various animal species for each fungus before this type of system could be put to wide-spread use in the production of protein.

A more direct application of fungal growth on animal wastes has been described by Seal and Eggins (1976). In their investigation, indigenous thermophilic fungi have used in an attempt to utilize cellulose and nitrogen in a mixture of pig slurry and straw in a pilot-scale system. After 14 days, during which time supplementary heat was applied to the mixture, the total protein content increased from 5 to 10 to 13%, and cellulose content was reduced. Total dry matter loss was not measured, but the reduction in cellulose and dry matter probably could account for the increase in total nitrogen content. A temperature of 50° C was sufficient to destroy coliforms, nonlactose fermenting and salmonella organisms in the mixture within 2 days. This temperature, plus a slightly alkaline pH, was also sufficient to suppress the growth of two pathogenic fungi, Aspergilus fumigatus and Mucos pusillus. No extensive nutritional evaluations of the final product have been made, but a preliminary trial with rabbits showed no particular problems with acceptability or toxicity.

18.3 Multicellular Organisms Utilized in Protein Production from Animal Wastes

Two multicellular invertebrates, the house-fly and the earthworm, have been used to process animal manure, and the resulting products appear to have some potential as a feed ingredient. The yields with both invertebrates were not particularly high, and the action of the organisms involved is one in which protein was isolated and little, if any, actual synthesis of new material occurred. The house-fly pupae or adult house-fly protein produced seems to be at least as good a protein source as soybean meal in chick diets. The earthworm protein has not been adequately tested to determine its value as a feed ingredient.

18.3.1 Coprophagous Insects - House-fly, Musca domestica L.

Lindner (1919) has the distinction of being one of the first to go on record in proposing the use of a coprophagous insect, specifically the common house-fly, to produce protein from human excreto. His plan was to raise larvae on excreta, harvest them, and utilize the dried larvae as a protein material. He conducted a few preliminary studies, but the project never progressed much beyond the speculative stages until Calvert et al. (1969) and Miller and Shaw (1969) reported on studies in which poultry manure was seeded with house-fly eggs, the eggs were allowed to hatch, and the resulting larvae and pupae were harvested and used as a protein source for the growing chicks. In later studies, Calvert et al. (1970, 1971) and Morgan et al. (1970) described the procedures used, pupae yields, changes that occur in manure during processing, comparison of dried pupae, and equipment used to harvest larvae and pupae.

The yield of pupae and larvae and the changes in composition of manures are shown in Table 18.9. Pupae were largest when a seeding rate of 1.5 eggs/g of manure was used. However, weight loss was not greatly affected by the rate of egg seeding. Manure weight loss was maximum when 4.5 eggs/g were used, but the average pupal weight and total pupae produced were reduced at that rate.

In an overall evaluation, a seeding rate of 3.0 eggs/g was selected. The average pupae weight, total pupae weight, and the amount of moisture and weight lost for this seeding rate were most favourable. The maximum yield of pupae plus larvae from these studies was about 3.2% of the fresh manure. Dry matter yield was approximately 4.0% on the basis of a 25% DM content for manure and a 32% DM content for larvae plus pupae. The percentage of nitrogen recovered in pupae was approximately 7.5% if a value of 5.6% is used for dried manure; 10.1% was used for larvae and pupae. Even though the yield of nitrogen was low, on the basis of the amino acid composition presented in Table 18.10, the quality of the protein appeared to be good. This composition suggests that this material should compare favourably with fish or meat meal as a protein source.

The results of an experiment in which dried pupae replaced all of the soybean meal in a chick diet are presented in Table 18.11. On the basis of these observations, fly pupae meal was as satisfactory a protein source as soybean meal. In fact, the chicks fed fly pupae meal in experiment 2 gained more and had a slightly better feed conversion than chicks fed soybean meal. However, this was a short-term study not yet confirmed by others.

Adult flies from pupae grown on chicken manure were also fed to chicks. Adult flies differed from pupae in that their protein content on a DM basis was 75% and fat content was 7%. Chick gains over a 3-week period week period were slightly better for chicks fed dried, ground, houseflies than for chicks fed soybean meal.

¹ 8-day growth period.
² Three experiments with three 200-g samples per treatment.
³ Determined by the Official Methods of the Association of Official Agricultural Chemists, 12th Ed., 1975, Washington, D.C.

Source: Calvert et al., 1971.

¹ Determined according to the Official Methods of the Association of Official Agricultural Chemists, 12th Ed., 1975, Washington, D.C.
² Nitrogen times 6.25
³ Primarily nitrogen-free extract and fibre.

Source: Calvert et al., 1971

Table 18.11 Growth and Feed Consumed by Chicks Fed Diets Containing Dried House-fly Pupae Meal or Soybean Meal

¹ Chicks fed diets for 7 days from 1 week of age.
² Chicks fed diets for 14 days from 1 day of age.
³ Values underlined are satisfically different (P < .005)

Source: Calvert et al., 1971.

This research showed that insects, specifically the house-fly, can be used to extract protein from manure. There is little probability that the larvae do anything more than remove protein from manure and make it somewhat more acceptable and available to animal species. The yield was certainly low, but the protein appeared to be of particularly high quality.

18.3.2 Earthworms

Some type of animal manure is generally used in the production of earthworms for fish bait, and this fact has suggested that under proper conditions earthworms might be used to process animal wastes and harvested for use as a high-protein feed ingredient. In one such experiment, conducted by Fosgate and Babb (1972), the common earthworm, Lumbricus terrestris, was used to degrade fresh, raw cow manure. The fecal material served as the only source of feed for worms, and they were maintained on this medium for about 1 year. Lime was added to maintain the medium at a pH of 7.0. The conversion rate of raw feces to worms was about 10:1 on a wet or dry matter basis. On the basis of information obtained in this study (see Table 18.12), a 100-head cow herd producing 3174 kg of manure/day would yield 42.3 kg of dried earthworm protein/day or 15 439 kg annually.

The manure residue remaining after digestion by the earthworms weighed only one-half that of the fresh manure. The manure residues were a satisfactory potting soil for use in growing flowering plants.

Space requirements might be a limiting factor in this system, but from the data presented it was not possible to determine what this might be. Such a system would also be limited to areas where winter temperatures are not severe enough to inhibit worm development. Another possible limitation would be harvesting methods, because no mechanical means has been developed that would satisfactorily collect the quantity of worms produced in a large-scale operation.

During the course of this study, dried worm meal was fed to cats which seemed to accept it readily. However, the dried worm has not been evaluated nutritionally, and its true value as a protein source remains to be determined. On the basis of the proximate analysis conducted, this material might have potential as a feed ingredient.

18.3.3 Miscellaneous Invertebrates

Dung beetles, scarab bettles, soldier flies, various blow-flies, and a variety of other insects are known to be scavengers and processors of animal manure. Their efficiency under natural conditions would suggest that they would have some potential for the controlled processing of animal wastes, but no reports on their use were found. A review of some of the procedures for maintaining colonies of these insects suggests that producing enough of any of them to process a significant amount of animal manure would be difficult and expensive. Until simplified procedures for rearing these insects can be developed, as for the house-fly, it is doubtful that they will be particularly valuable in the processing of animal manures with the production of useful protein products.

Table 18.12 Average Mineral Composition of Cattle Feces, Earthworms, and Earthworm Dirt (%DM)

¹ Earthworms analyzed 22.9% dry matter containing 58.2% protein, 3.3% fibre, and 2.8% fat.

Source: Fosgate and Babb, 1972.

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