Chapter 3
HEALTH HAZARDS AND SAFETY CONSIDERATIONS

Bureaucracy defends the status quo long past the time
when the quo has lost its status.

L. Peter

3.0 GENERAL

The reservations regarding feeding animal wastes are usually based on ethical and aesthetic grounds as well as on logical assumptions of potential risks related to the nature of the waste biomass, its high bacteriological activity, the accumulation of anti-metabolites, drugs and other non-nutritional excretory products partly derived from the ration.

The great concern lies in the excessive accumulation of macrominerals (Ca, Si, Fe), trace elements (Cu, Mn, Zn, Se), heavy metals (Pb, Hg, Cd), medicinal drugs (antibiotics, coccidiostatics, sulfa drugs, etc.), insecticides, herbicides, wood preservatives, mycotoxins and hormones, and also in the presence of harmful organisms transmittable via wastes to other animals and to man.

These problems, however, do not relate to wastes alone: conventional feeds may contain a large number of contaminants in the form of phytotoxins, pesticides, pathogens and other xenobiotics.

The digestive tract, its microflora, the liver, the kidneys and other organs of the body have a considerable metabolic capacity to remove, break down, transform or change, partly or completely, metabolic wastes. Recent studies of Thomasson and Yokohama (1978), referring to U-14C phenol as a model compound for tracing the metabolic fate of faecal waste, showed that “virtually all the tracers had been conjugated as glucoronide and sulfate esters.” The authors stated that certain rumen organisms deconjugate the metabolites produced.

In follow-up toxicological research involving feeding dried layer manure (at 30% level on DM basis) to steers for 180 days, Kinzell et al. (1978) found that all physiological parameters (blood, urine, serium indicator enzymes, pathological examination of tissues, microsomal mixed-function oxidase activities in post mortem liver) were normal.

Over two decades of experimental and field observations have so far produced no scientific evidence to show that animal-waste recycling poses any health risks (Fontenot and Webb, 1975) provided the waste is properly processed and the ration carefully balanced (Müller, 1974).

3.1 ACCUMULATION OF MINERALS

An excessive accumulation of minerals in faecal wastes is encountered when a high level of minerals is fed to animals (calcium in layers, copper in broilers and young poultry, and copper and zinc in pigs). Repeated recycling of manure within the same species also increases the accumulation.

In principle, the level of mineral elements in faecal wastes is related to the levels of the elements in the ration (see Table 75).

Table 75
CRITICAL MINERALS: DIETARY AND FAECAL LEVELS
(on DM)

Since sheep tolerate a much lower copper level in their diet (below 200 ppm) than other livestock species, a potential danger exists particularly when higher levels of broiler litter are incorporated in their ration (Fontenot et al., 1971). However, in countries where rations for broilers or other poultry (or pigs) are not supplemented with high copper levels, this problem does not exist.

The author has observed that trivalent iron (present in oil palm fibre - “fines”) was deterimental to cattle performance when fed above 600 ppm level; in addition to growth depression, a clinical manifestation of vitamin A deficiency was observed. No difficulties arose when bivalent iron was used above the 2,000 ppm level (Müller, unpublished results 1975).

Virginia researchers (Westing et al., 1977 and 1978) have studied the fate of 43 minerals derived from feeding rations comprising 30% broiler litter or 16% beef feedlot waste (see Table 76).

Table 76
MINERAL PROFILES IN LIVER FROM STEERS FED BROILER LITTER
AND BEEF FEEDLOT WASTE (ppm DM)

Source: ¹ Westings et al., 1977;
² Westings et al., 1978.

The content of mineral elements in liver tissue as a result of waste feeding changed quite considerably in some instances, but most of the minerals studied were within their tolerance levels for cattle.

The fate of arsenic from animal waste, with and without bedding, has been studied by several authors (Morrison, 1969; El-Sabban et al., 1970; Calvert and Smith, 1972; Webb and Fontenot, 1975; Calvert 1973, 1975; Caswell et al., 1976). Levels of arsenic accumulated in the animal tissue were always much below the safe, permissible level, and were markedly reduced by a withdrawal period five days prior to slaughter. Recently Caswell et al. (1978) reported low arsenic levels in litters with higher moisture contents, but ensiling itself had no effect on the arsenic content.

Lead, mercury and cadmium are usually accumulated during the settling process (sludge). They are rarely found in excessive levels in poultry waste, but higher contents have been found in beef manure. The toxicity of lead depends greatly upon the chemical nature of the compound and thus its absorption by the body. An injection of 400 grammes of metallic lead during a period of 4 months did not kill a calf, which in fact showed no evidence of illness (Gibbons et al. 1970). Similarly, municipal sludge containing 120 ppm lead, when fed to cattle at 25% level for 150 days, did not affect their health or performance. Lead was almost totally excreted and not traceable in muscles, liver or kidneys (Müller, 1975).

The accumulation of minerals in animal wastes is thus a relatively minor problem within the context of the potential health hazards of waste recycling. In formulating rations it is however necessary to limit quantities of animal wastes so that the content of critical mineral contaminants does not exceed tolerance levels.

3.2 ANTIMICROBIAL DRUGS

Antibiotics and other antimicrobial drugs (sulfa drugs, coccidiostatics, etc.) have been used for the past 30 years, mainly for poultry and pigs. They are excreted via the intestinal and urinary route. Their activity (depending upon their chemical structure) changes during digestion and other metabolic processes and after excretion. Processing, temperature, humidity and pH of the excreted faecal waste are the most significant exogenous factors responsible for the level of drugs found. Many drugs form chemical complexes (e.g. with Ca) which render them insoluble, so that their absorption by the body is either low or nil. Some drugs analytically detected in wastes are physiologically inactive.

Brugman et al. (1964), in an experiment with laying hens, fed rations containing various drugs (arsanilic acid, zoalene, unistat, nicarbazin, furan and sulfaquinoxaline) but did not detect any residues of these drugs except arsanilic acid, in the litter. Morrison (1969) studied the fate of organo-arsenicals as a feed additive to broiler rations. Although they were found in the litter, the quantities detected were so low as to create no arsenic hazard.

Messer et al. (1971) detected furan derivatives in poultry litter from various farms. The furazolidone level ranged from 10.2 to 21.5 ppm, and nitrofurazone from 4.5 to 26.7 ppm. Donoho (1975) reported that 75% of the monensine incorporated as a rumen stimulant into steers' rations was found in the faeces. In dehydrated wastes from poultry fed monensin, a concentration of 10–15 ppm, was found, but Caswell et al. (1978) reported that monensin sodium fed to broilers was detected neither in the litter nor in the litter silage.

Brugman et al. (1967) reported that no residual amprolium or arsenic was found in the heart, spleen, 12-rib, kidney, kidney fat, liver or brain of lambs fed rations containing poultry litter from birds whose diet contained these drugs.

Chlortetracycline (CTC) balance and its fate was studied by Müller et al. (1967). Broilers fed a starter and finisher containing 60 and 50 ppm CTC respectively, produced litter with an average of 8 ppm CTC. The litter was incorporated at 40% level into a completed beef cattle feed which thus contained 3.2 ppm CTC. The antibiotic was not found in blood, liver, kidney, muscles and other tissues, but traces were detected in the faecal excreta. Elmund et al. (1971) reported that 75% of CTC in the steer ration was excreted.

Webb and Fontenot (1975) investigated the content of several antimicrobial drugs in broiler litter collected from poultry farms in Virginia. Their findings are presented in Table 77. The wide range of concentrations of individual drugs could be attributable to the level of drug fed and perhaps other factors (litter age, litter treatment, bedding, medication, etc.). Zinc bacitracin activity was also detected in the litter from farms where this drug was not supplemented.

Table 77
ANTIMICROBIAL DRUGS IN BROILER LITTER

¹ Used continuously in broiler diets.
² Used intermittently in broiler diets.
³ Used in broiler diets.
⁴ Not used in broiler diets.

In other studies Webb and Fontenot (1975) investigated the problem of feed additive residues in animal tissues. They detected negligible levels of CTC in the tissue of some steers (0.034–0.041 ppm), but most of the steers fed broiler litter at 25 and 50% levels in the ration showed no residual CTC in their tissues. Nicarbazin and amprolium contained in the litter were not detected in steer tissues.

Most researchers agree that residues of antimicrobial drugs in animal wastes pose little danger because their retention by animal tissues is much below the safety level, or even nil. The only problem may arise when broiler waste is fed at higher levels to dairy cows, where regulations establish a zero tolerance of drugs in milk.

3.3 PESTICIDES

A large number of pesticides are used in farms and agro-related industries. They include aldrin, BHC isomers, lindane, chlordane, DDT, dieldrin, endrin, heptachlor, methoxychlor, toxaphene and many others. They are used for ectoparasite control; endoparasite control (oral or parentheral); treatment of feed or bedding prior to or during manufacture; spraying manure, litter or the entire environment for pest control; spraying or treating crops by insecticides and herbicides; wood preservatives; fire retardants (polybrominated biphenyl); and many other applications on farms and in the feed industry and other activities related to farming. The oral toxicity and residual storing capacity of these insecticides in fat tissues is well established.

A comprehensive study of the fate of residual pesticides in broiler litter was carried out by Fontenot et al. (1971). The results of these authors, as related to maximum non-toxic and minimum toxic levels for cattle established by Gibbons et al. (1970), appear in Table 78.

Table 78
EFFECT OF FEEDING BROILER LITTER ON PESTICIDE RESIDUES
IN STEER LIVER AND OMENTAL FAT

Source: ¹ Fontenot et al., 1971.
² Gibbons et al., 1970.

These data indicate that the level of pesticides is often higher in cattle fed conventional feed ingredients than in cattle fed poultry litter or other animal wastes. This is because the use of pesticides in agriculture is widespread, and high levels may often occur in forage, feed and crop residues (straw). The latter, when used for bedding, may contribute to the quantity of pesticides found in the litter or in the tissues of livestock fed animal wastes.

In summary, however, pesticides in livestock waste feeding apparently represent no serious threat to humans. Pesticides are commonly used in agriculture and often occur in higher levels in conventional feeds and forages than in animal wastes.

3.4 MYCOTOXINS

The feeding value of animal wastes can be seriously affected by mycotoxins and other metabolites of several species of Aspergillus and other genera, such as Penicillium. These micro-organisms can be found in large populations in wastes or in bedding material prior to its use. The most common are Aspergillus flavus and A. niger; hoth produce aflatoxin and other mycotoxins. They grow on all kinds of livestock wastes and bedding material, and when consumed in quantity they may have direct effects on such organs as the mucous membrane, digestive tract, nervous and blood system, etc.

Similarly, genera of Stachybotrys, being saprophytes on straw and bedding material, may cause specific symptoms of disease in individual livestock species. Pithomyces charterum, another saprophyte growing on cellulosic material, produces toxins dangerous to all species. Claviceps purpurea, growing mostly in temperate regions, produces alkaloids, ergotoxin and histamin. Basidiomycetes also grow on cellulosic materials, and their toxins can occur in hulls and bedding material prior to their use.

Nevertheless the growth of these micro-organisms is subject to moisture content of the host material, as their growth is inhibited when the moisture content is below 25% or above 40%. This in turn depends on the physical structure of the waste or bedding and the height of storage of the material.

Hendrickson and Grant (1971) detected more aflatoxin in fresh feedlot manure than in partially decayed or stockpiled manure. No residues of aflatoxin were found in composted manure. The authors reported that aflatoxin was absorbed by rapid sand filtration and was inactivated by chlorination.

Aflatoxin levels found in samples of poultry litter, collected in several Southeast Asian countries, varied between 50 and 500 ppm (Müller, 1975). Drying and other processing of waste stops the microbial growth, but the inactivation of the actual toxin can be partially eliminated by microbial processes, although the mode of action is unknown. Nevertheless, even samples of broiler litter high in aflatoxin (360 ppm), when fed to steers for an entire finishing period (172 days), produced no noticeable symptoms of aflatoxicity (Müller, 1967).

Bell (1975) studied fungi profiles in feedlot waste and found that a large number of thermophilic and mesophilic fungi which are pathogenic or toxigenic to animals and plants are normally present in feedlot surface manure. Thermophilic fungi (Mucor pusillus, lanuginosa, Talaromyces thermophilius, and Chaetomium thermophile) were found, and their population remained practically unchanged over a two-month period during which samples were collected seven times. Mesophilic fungi of the genera Mucor, Rhizopus, Absidia and Mortierella were mostly present at lower temperatures and in fresh faeces.

The moisture content appears to be a factor responsible for the degree of infestation: it was observed that A. flavus and Fusarium solani were found in increased numbers when moisture of the feedlot waste increased.

The magnitude of the problem of mycotoxins in animal waste is similar to that of mycotoxins in feed. The presence of mycotoxins in waste creates a particular problem at the time of waste collection, when the biotop changes. Drying, ensiling or other processing should therefore take place immediately after disposal of the wastes.

3.5 HORMONE RESIDUES

In experiments on chicks, Riley and Hammond (1942) reported that precocious comb and wattle growth resulted when either dried cow faeces or their 60% alcohol extract was incorporated in the chick diet. In follow-up studies it was observed that the development of testicles and ovaries was retarded when chicks were fed dried cow faeces, but not when they were fed faeces from mature bulls.

Westing and Brandenberg (1973) fed a ration containing 14% beef feedlot waste to cattle, and no residues of estrogens were detected in this ration.

Estrogens were detected in livestock wastes by Story et al. (1957). Lambs fed 1 mg of diethylstilbestrol (DES) per day excreted 76% of the total daily dose, and lambs fed 2 mg excreted 84% of the dose. Similar results were reported in an experiment by Callantine et al. (1961), with cattle fed 10 mg DES. The level of estrogen being related to the stage of the estrus cycle, more estrogens were always found in the urine of cows in heat (Mellin and Erb, 1966).

Erb et al. (1968) reported a consistent increase in the rate of estrogen during the first seven months of gestation. Mathur and Common (1969) reported measurable quantities of estrone and estradiol-17B in layer manure. The secretion of hormones was higher in laying than in non-laying hens.

The presence of androgenic and estrogenic activity in poultry manure was reported by Calvert et al. (1978). Using chick comb growth and rat uterine growth, the authors bioassayed cage laying-hen excreta processed by fly larvae and found an androgenic activity equivalent of 2.18– 9.36 μg of testosterone per gramme of dried excreta. This hormonal activity derived from larvae biodegradation, because androgenic activity was not present in the fresh manure of layers. Drying (48 hours at 100°C) did not eliminate the activity. In rat uterine growth assays, Calvert et al. (1978) found that cage laying-hen manure exhibited 1.6 μg of estradiol equivalent per gramme of dry dehydrated manure. The authors reported that holding fresh laying manure for 5 to 7 days, under aerobic or anaerobic conditions, reduced estrogenic activity, but drying up to 100°C had no effect.

Sexual hormones in pig waste (as a result of heat or their use for estrus synchronization) were reported by Hennig and Poppe (1977), but feeding the waste to steers produced no morphological changes attributable to these hormones.

The problem of hormone residues in animal wastes is of the same magnitude as that of their presence in some forages or feeds. There is so far no evidence that traces of hormonal activity in some animal wastes pose any danger to the livestock fed the wastes, or to man as a consumer of subsequent animal products.

3.6 DISEASE TRANSMISSION

There are many unanswered questions with regard to animal wastes as agents of disease transmission, and information on basic research is still lacking. There are enormous differences of opinion between the epidemiologist on the one hand and the animal grower on the other. While the epidemiologist treats animal wastes as a reservoir of pathogenic and non-pathogenic organisms dangerous to animals and/or man (Strauch, 1977), the view of the animal production community is that interspecies or monospecies coprophagy always existed in nature, that animals are always in close contact with their own wastes, and that conventional feed ingredients (meat and bone meal from condemned carcasses, fish meal, blood meal and many others) are not always free of pathogens.

Halbrook et al. (1951), in their early bacteriological studies, reported that reused litter exhibited lower counts of coliforms, lactobacilli and enterococci than new bedding material, used only for one batch of birds (8 weeks). Exposure of poultry waste to 30 and 37°C for one week eliminated yeasts and sharply reduced moulds.

Similarly, Botts et al. (1952) reported that the survival time of Salmonella spp. was 15 to 20 days in old litter but 70 and 63 days in new litter. Over 200 strains of Clostridium perfringens were isolated from cattle manure by Niilo and Avery (1963). Bacteriological examination of 44 samples of poultry litter (Alexander et al., 1968) showed 10 different species of Clostridium, 2 of Corynebacterium, 3 of Salmonellae, one Actinobacillus sp., one yeast and 2 Mycobacterium spp. In all 44 samples Enterobacteriaceae (other than Salmonellae) Bacillus spp., Staphylococcus spp. and Streptococcus spp. were detected.

Carriere et al. (1968) reported that Mycobacterium avium survival was shorter in autoclaved litter than under normal litter conditions. The authors expressed the opinion that definite self-sanitation properties exist in the biotop litter. Strauch and Mueller (1968), in an artificial model, seeded 3 Salmonellae spp. and stored them in metal drums; in summer when the temperature range was from 16 to 23°C, the organisms were destroyed in 6 days, while in winter, at temperature range 5 to 11°C, they survived for 26 days. Salmonellae were detected in 26% of 91 samples collected from poultry farms; populations in individual samples ranged from 1 to 34,000 per g (on DM); more were found in poultry manure from cages than in samples from floor housing (Craft et al. 1969).

In early studies Ciordia and Anthony (1969) showed that the ensiling process eliminates nematodic parasites almost completely within days after ensiling. Many authors report that faecal coliforms and Salmonellae are destroyed at the latest within 10 days of ensiling, but not so the spore-forming bacteria. Recent research of McCaskey and Anthony (1978) identified 65 clostridial cultures isolated from an ensiled mixture containing 36% steer manure. The predominant species was C. sporogenes (23% of the identified isolates); other species represent less than 10% of identified isolates. C. sporogenes however existed at similar levels in ensiled maize forage alone (without steer manure or other animal wastes) at levels comparable to those in steer manure-based silage. It was observed that the rate of decline, as a result of the ensiling process, was similar as between conventional forage silage and manure-based silage. The authors concluded: “…if C. sporogenes is indicative of a potential health risk of C. botulinum in ensiled bovine manure-formulated feed, it appears that the risk also exists in corn silage.”

In extensive studies at Michigan State University (Zindel, 1970), Bacillus spp., Proteus spp., E. coli and other Enterobacteriaceae were isolated from 40% of fresh layer manure and coliforms were detected in 60% of the samples. Lovett et al. (1971) isolated 17 genera of fungi, with a predominance of Penicllium, Scopulariopsis and Candida, of which 12 species were isolated from poultry feeds. Salmonellae were not detected, but coliform and E. coli were present in all samples.

Messer et al. (1971) reported that S. typhimurium, S. pullorum, Arizona sp. and E. coli were destroyed at different temperatures and time exposures, but that 68.3°C for 60 minutes was effective in destroying all potentially dangerous pathogens. The most resistant was S. typhimurium. Fontenot et al. (1971) reported that drying at 150°C for a minimum of 3 hours sterilized litter. Shorter exposure (1 or 2 hours), lower temperature (100°C for up to 48 hours) autoclaving or fumigation (with beta-propiolactone or ethylene oxide) were ineffective.

Minnesota scientists, studying the survival of leptospires in cattle manure, found that the leptospires survive for 61 days in the oxidation ditch, because the aerobic process increases pH to favourable levels. The optimum pH range for leptospire survival is 7.2 to 7.4; a pH of less than 5 or greater than 8.5 is detrimental (Diesch, 1971).

Harry et al. (1973) found that methyl bromide fumigation was effective in the destruction of S. typhimurium. Higher moisture accelerated the effect, while reducing temperatures from 25°C to 10°C reduced effectiveness.E.coli proved to be more resistant to fumigation than S. typhimurium. S. staphylococcus and coliform tests were negative when broiler litter was ensiled (Creger et al., 1973). Similarly, Caswell et al. (1974, 1977 and 1978), Harmon et al. (1975), and Duque et al. (1978) found ensiling of poultry litter to be the most effective means of total elimination of coliform Salmonella-type organisms (Wilkinson, 1978) and that it also resulted in a substantial reduction of the total bacterial count.

Temperatures and exposure times generally considered (Müller, 1975) sufficient for the destruction of certain pathogens and parasites are as follows:

Salmonella spp. stop development above 46°C and are dead within 30 min. at 55-60° or within 20 min. at 60°C.

Shigella spp. are dead within 1 hour of exposure to 55°C.

Entamoeba histolytica (cysts) are dead within a few minutes at 45°C and within a few seconds at 55°C.

Taenia saginata is dead within a few minutes at 55°C.

Trichinella spiralis is killed quickly at 55°C and instantaneously at 66°C.

Brucella abortus Bang is dead within 3 min. at 62–63°C and within 1 hr. at 55°C.

Micrococcus pyogenes (var. aureus) is dead within 10 min. at 50°C.

Streptococcus pyogenes is dead within 10 min. at 54°C.

Mycobacterium tuberculosis is dead within 15 to 20 min. at 66°C or within a few instants at 67°C.

Corynebacterium diphteriose is dead within 45 min. at 55°C.

Necator americanus is dead within 50 min. at 45°C.

Ascaris lumbricoides (eggs) is dead within less than 1 hr. at temperatures above 50°C.

These well established facts show that animal wastes treated by heat, ensiling or other processes are safe. Subsequent research and field studies proved without doubt that ensiling of animal wastes, although the simplest method, is most effective in eliminating potential pathogens such as parasites and faecal coliforms and generally in lowering the total microbial count.

The CAST report (1978) reaches the following conclusions regarding the danger of disease transmission through feeding animal wastes:

“The animal body is protected in various ways from the pathogens it might encounter in consuming animal wastes. These mechanisms include:”

1. Lining of the digestive tract with contiguous cell layers that prevent the entrance of the pathogens into body tissue unless injury to the cell layer occurs.
2. Digestive enzymes and marked variations in pH within the digestive tract are lethal to many potential pathogens.
3. The high microfloral population of the first three stomach compartments of ruminants, which inhibits the multiplication of pathogens.
4. The immune system of the body. This system recognizes pathogens after the first encounter and then effectively neutralizes those pathogens when the body is exposed to them on subsequent encounters. This mechanism is especially important for pathogens from animal wastes fed to the same species because many of these pathogens are so common that animals acquire an early immunity to them. Ruminants in feedlots commonly ingest their own waste by licking the packed waste in pens, by licking their coat to which waste has adhered, and by feed from feed bunks that have been contaminated by waste blcwn into the bunks.

“An additional protective mechanism is the requirement for ingestion of a “minimum infective dose” before an infection can become established. If waste from a group of animals is fed to the animals, and if one of the animals is shedding a pathogen, it is unlikely that any one animal will obtain the minimum infective dose of this particular pathogen.”