Feed Toxins & Contaminants: A Complete Pharmacy Guide
01What is a poison?
Poisons are substances that cause disturbances in organisms — usually through chemical reactions or other activities at the molecular scale — when an organism absorbs a sufficient quantity. The field of medicine (particularly veterinary medicine) and zoology distinguish a poison from a toxin, and from a venom.
Toxins are poisons produced by organisms in nature. Venoms are toxins injected by a bite or sting — a delivery method exclusive to animals. The key difference between venom and other poisons is precisely this delivery method. Industry, agriculture, and other sectors use poisons for reasons other than their toxicity.
02Animal feeding stuffs explained
Animal feeding stuffs refer to any material used as food — especially for animals. It is the food for domestic animals and livestock in the course of animal husbandry. There are three basic types:
- Fodder — foods or forages given to animals (including plants cut and carried to them) rather than that which they forage for themselves. Examples: hay, silage, straw, compressed and pelleted feeds, oils, mixed rations, sprouted grains and legumes.
- Forage — plant material (mainly leaves and stems) eaten by grazing livestock. Includes crop residue, immature cereal crops, hay and silages.
- Compound feeds — fodder blended from various raw materials (corn, soybeans, sorghum) and additives, formulated according to the specific requirements of the target animals. May include premixes of vitamins, minerals/chelates, chemical preservatives and antibiotics.
Feed grains are the most important source of animal feed globally — the two most important being maize and soybeans. Other feed grains include wheat, oats, barley and rice. Traditional sources include household food scraps and by-products of food processing such as brewing of peanuts, soy and corn for pap/akamu.
03Major sources of feed contamination
Animal feeds are routinely subject to contamination from diverse sources — environmental pollution and the activities of insects and microbes. They may also contain endogenous toxins arising from specific primary and secondary substances produced by fodder plants. Feed toxins therefore include compounds of both plant and microbial origin.
Although these toxins are often considered separately because of their different origins, they share several common underlying features. Particular compounds within both plant and microbial toxins may exert anti-nutritional effects or reduce reproductive performance in farm animals. The combined effects may be the result of additive or synergistic interactions between the two groups.
Environmental contaminants · Bacterial contaminants · Fungal contaminants · Mycotoxins · Plant toxins · Weed seeds · Animal toxins · Undeclared additives.
04Environmental contaminants
A wide range of organic and inorganic compounds may occur in feedstuffs, including pesticides, industrial pollutants, radionuclides and heavy metals.
Pesticides
Pesticides that may contaminate feeds originate from most of the major groups, including organochlorines, organophosphates and pyrethroids. Although pesticides are potentially toxic to farm livestock, the primary focus of concern centres on residues in animal products destined for human consumption.
Industrial pollutants
Industrial pollutants that contaminate feed (particularly herbage) include dioxins and polychlorinated biphenyls (PCBs). Cows grazed on pastures close to industrial areas will likely have higher dioxin content than cows from rural farms. Today people are exposed to dioxins primarily by eating food — in particular animal products — contaminated by these chemicals. Dioxins can cause reproductive and developmental problems, interfere with hormones and cause cancer, because they decompose slowly in the environment.
Heavy metals
Heavy metals such as cadmium, lead and mercury poison animals through direct contact (inhalation, ingestion and absorption). They accumulate in the body, disrupt metabolic functions, and can develop carcinogenicity, mutagenicity, embryotoxicity, hepatotoxicity and renal toxicity. Cadmium may occur from applying certain types of fertilizers to crops and pastures. Lead contamination arises from industrial and urban pollution, while mercury in feeds arises from the use of fish meal.
Radionuclides
Radionuclide contaminants include caesium-134 and caesium-137. They cause an increase in mutation rate in animals.
05Bacterial contaminants
Faecal contamination of feed is widespread on farms and is an important route of poisoning in animal feeding stuffs, since animals are exposed to Escherichia coli, Salmonella enterica spp. and Campylobacter spp. Bacterial contamination is likely to be minimized — or even eliminated — through heat-processing of feed before distribution to farm animals.
Listeria monocytogenes tends to occur in poor-quality silages and big-bale silages due to aerobic fermentation and raised pH levels, which encourage the growth of Listeria. However, when grass is ensiled under anaerobic conditions, the low pH regime ensures that Listeria is excluded from the resulting silage.
Contamination of silage with Listeria is important as it causes abortion, meningitis, encephalitis and septicaemia in animals and humans.
06Fungal contaminants & mycotoxins
There are several reports worldwide of contamination of animal feeds with fungi and their spores. In the tropics, Aspergillus is the predominant genus in dairy and other feeds. Other species include Penicillium, Fusarium and Alternaria, which are also important contaminants.
Mycotoxins are secondary metabolites of fungi that have the capacity to impair animal health and productivity. The diverse effects precipitated by these compounds are conventionally considered under the generic term mycotoxicosis and include distinct syndromes as well as non-specific conditions.
Moisture content and ambient temperature are key determinants of fungal colonization and mycotoxin production. Contamination of forages and cereals frequently occurs in the field following infection of plants with particular pathogenic fungi or with symbiotic endophytes. Contamination may also occur during processing and storage of harvested products and feed whenever environmental conditions are appropriate for spoilage fungi.
Toxigenic fungi — two classes
- Field or plant-pathogenic organisms — Claviceps, Neotyphodium, Fusarium, Alternaria.
- Storage or saprophytic/spoilage organisms — Aspergillus and Penicillium.
07The six major mycotoxin classes
Aflatoxins (AF)
Aflatoxins are mycotoxins produced by Aspergillus species of fungi such as A. flavus and A. parasiticus. The umbrella term refers to four types — B₁, B₂, G₁ and G₂ (AFB₁, AFB₂, AFG₁ and AFG₂). In addition, aflatoxin M₁ has been identified in the milk of dairy cows consuming AFB₁-contaminated feeds.
AFB₁, the most toxic, is a potent carcinogen and has been directly correlated to adverse health effects such as liver cancer in many animal species. Aflatoxin-producing Aspergillus are generally regarded as storage fungi, proliferating under relatively high moisture/humidity and temperature. Contamination is therefore almost exclusively confined to tropical feeds such as oilseed by-products derived from groundnuts, cotton seeds and palm kernel. Aflatoxin contamination of maize is also an important problem in humid regions where A. flavus may infect the crop prior to harvest and remain viable during storage.
Ochratoxins (OT)
Ochratoxins are mycotoxins that come in three secondary metabolite forms — A, B and C (OTA, OTB, OTC) — produced mainly by Aspergillus ochraceus and at least two Penicillium species. OTA and OTB occur naturally as contaminants, with OTA more ubiquitous, occurring predominantly in cereal grains and in the tissues of animals reared on contaminated feed. Aspergillus ochraceus is found as a contaminant of a wide range of commodities including beverages such as beer and wine.
Citrinin
Citrinin is another mycotoxin produced by certain species of Aspergillus and Penicillium. Citrinin and ochratoxins are nephrotoxic to animals. Although associated with many foods (wheat, rice, corn, barley, oats, rye and food coloured with pigments), its full significance for human health is unknown.
Ergot alkaloids
Ergot alkaloids are a toxic mixture of alkaloids in the sclerotia of Claviceps species — common pathogens of various grass species. Ingestion of ergot sclerotia from infected cereals causes ergotism, which occurs in two forms:
- Gangrenous — affecting blood supply to the extremities.
- Convulsive — affecting the central nervous system.
Ergotism as a human disease is reduced, but it remains an important veterinary problem.
Patulin
Patulin is a toxin produced by Aspergillus, Penicillium and Paecilomyces fungal species, with P. expansum especially associated with a range of moldy fruits and vegetables. Although patulin has been shown to be carcinogenic, it has also been reported to damage the immune system in animals.
Fusarium toxins
Fusarium toxins are produced by many species of Fusarium:
- Fumonisins — affect the nervous systems of horses.
- Trichothecenes — most strongly associated with chronic and fatal toxic effects in animals and humans.
- Zearalenone — not correlated to any fatal toxic effects in animals and humans.
08Plant toxins in animal feed
Many plant components have the potential to precipitate adverse effects on the productivity of farm livestock. These compounds are present in the foliage of virtually every plant used in practical feeding. Plant toxins fall into two broad groups based on their response to processing heat:
Heat-labile group
- Lectins
- Proteinase inhibitors
- Cyanogens
Heat-stable group
- Antigenic proteins
- Condensed tannins
- Quinolizidine alkaloids
- Glucosinolates
- Gossypol
- Saponins
- Non-protein amino acids
- Phyto-oestrogens
Plant toxins have anti-nutritional properties and each has a typical concentration at which it precipitates adverse effects.
Heat-labile plant toxins
Lectins are proteins capable of damaging the intestinal mucosa. In contrast to most other dietary proteins, lectins resist digestive breakdown, and substantial quantities may be recovered intact from the faeces of animals fed diets containing certain legume seeds. The prime example of a lectin with potent anti-nutritional and toxic properties is concanavalin A, a component of the jack bean. Lectins are also present in other legume grains including winged bean and soybean.
Proteinase inhibitors are typical examples of heat-labile anti-nutritional factors. They are present in leguminous seeds such as field beans, winged beans, pigeon pea and cowpea. Effects in animals include reduced protein digestion and endogenous loss of amino acids with overall impairment of performance.
Cyanogens occur widely in plants and in diverse forms. In sorghum and cassava, the predominant cyanogens are dhurrin and linamarin respectively. Linamarin is also present in linseed. Cyanogens are glycosides that readily yield hydrogen cyanide (HCN), and it is this latter molecule that causes dysfunction of the central nervous system, respiratory failure and cardiac arrest.
Heat-stable plant toxins
Antigenic proteins — certain storage proteins of legume seeds are capable of crossing the epithelial barrier of the intestinal mucosa to elicit adverse effects on immune function in farm animals. In soybean, the antigenic proteins have been identified as glycinin and conglycinin. These resist denaturation by conventional thermal processing. Effects include abnormalities in movement, indigestion, impaired nutrient absorption and predisposition to diarrhoea.
Condensed tannins (CTs) are widely distributed in leguminous forages and seeds and in sorghum. Cattle and sheep are sensitive to CTs, while goats are more resistant. Primary effects include impaired rumen function and depressed intake, wool growth and live-weight gain. However, at moderate levels (30–40 g CTs/kg legume dry matter), CTs may result in nutritional advantages — increased bypass protein availability and bloat suppression in cattle.
Quinolizidine alkaloids occur in lupins and include lupinine, sparteine and lupanine. Cattle consuming certain lupin species during pregnancy may produce calves with multiple congenital deformities.
Glucosinolates are glycosides found in forage crops such as kale. The most common breakdown products are isothiocyanates and nitriles, but depending on pH, temperature and metallic ion concentration, a number of other metabolites may also be produced. These products may then cause organ damage, goitrogenic effects or reduced feed intake — particularly in non-ruminant animals.
Gossypol is a pigment that occurs in cotton seed in free and bound forms. Free gossypol is a toxic entity and causes organ damage, cardiac failure and death. Cottonseed meal fed to bulls can induce increased sperm abnormalities and decrease sperm production.
Saponins — divided into two groups
- Steroidal saponins — occur as glycosides in certain pasture plants such as Brachiaria decumbens and Panicum species. Many hepatogenous photosensitization conditions in sheep have been attributed to forage plants containing steroidal saponins.
- Triterpenoid saponins — found in soybean and alfalfa. Triterpenoid saponins from alfalfa reduce feed degradation in the rumen.
Non-protein amino acids — a wide range of these occur in the foliage and seeds of plants. Forage and root brassica crops contain S-methyl cysteine sulphoxide (SMCO), while the aromatic amino acid mimosine occurs in the foliage and seeds of the tropical legume Leucaena leucocephala. Uncontrolled feeding of brassica forage to ruminants causes organ damage with haemolytic anaemia. Abrupt feeding of Leucaena to sheep causes shedding of fleece, reduced intake, organ damage and death. In cattle, loss of hair, excessive salivation, lethargy, weight loss and enlarged thyroids are common features of Leucaena toxicity.
Phyto-oestrogens are found primarily in forage grain legumes. In clover, formononetin is the major form. Phyto-oestrogens have been associated with "clover disease" in sheep, characterized by low ovulation and conception rate.
09Weed seeds as feed contaminants
Contamination of animal feeds with weed seeds is a major problem worldwide. The impact of weed seeds arises from the toxins they contain and from their diluent effects on nutrient density of feeds. The toxins include alkaloids, saponins, amino acids and proteinase inhibitors. Examples of weed seeds include those of Datura spp., common vetch, castor plants and Crotalaria spp.
10Animal toxins & prion diseases
The prion protein of mammalian meat-and-bone meal is a major feed contaminant causing fatal neurological lesions in a wide range of species. Bovine spongiform encephalopathy (BSE) is a major disease of cattle and is attributed to feeding cattle with meat-and-bone meal prepared from the carcasses of scrapie-infected sheep.
BSE in cattle, scrapie in sheep, and their human equivalent — new variant Creutzfeldt-Jakob disease (vCJD) — are all characterized by the accumulation of prion proteins. The incidence of CJD in humans has been linked to the consumption of BSE-infected beef. It is this association that has led to extensive and stringent legislation in the European Union concerning the use of specified animal products in livestock feeding.
The feed-to-food prion pathway remains one of the strongest arguments for strictly regulated rendering and feed-ban policies. Where such controls are weak, the risk of cross-species transmission rises.
11Undeclared additives & drug residues
Animal products are frequently contaminated with drug residues administered through the feed. Such feed additives may be used for disease control and the enhancement of livestock performance. Residues may also arise through contamination of animal feeds with undeclared drugs — mostly due to cross-contamination in feed mills. For example, medicated feed residues may be retained within equipment and then contaminate subsequent batches of feed.
Under these conditions, levels of contamination may be low but sufficient to cause detectable residues in animal products. The contaminants most frequently identified include:
- Chlortetracycline
- Sulphonamides
- Penicillins
- Ionophores
Drug residues in animal products are undesirable because of human health implications concerning allergies and the development of antibiotic resistance in disease organisms.
12Therapeutic substances in animal feeding stuffs
Therapeutic substances in animal feeding stuffs are mostly antimicrobial agents/antibiotics and antifungals. These agents are used in the husbandry of livestock for several purposes:
- Therapeutic — treatment when ill.
- Metaphylaxis — treatment of a batch of animals when at least one is diagnosed as ill.
- Prophylaxis — preventive treatment against diseases.
- Growth promotion — the use of subtherapeutic doses in animal feed and/or water to promote growth and improve feed efficiency. This use is being discouraged and has been banned in Europe and other developed countries.
Antibiotics currently used in animal feed
Chlortetracycline, procaine penicillin, oxytetracycline, tylosin, bacitracin, neomycin sulfate, streptomycin, erythromycin, lincomycin, oleandomycin, virginiamycin and bambermycins.
In addition to these antibiotics of microbial origin, there are other chemically synthesized antimicrobial agents also sometimes used in animal feeds. These include three major classes:
- Arsenical compounds — e.g., arsanilic acid and sodium arsanilate.
- Nitrofuran compounds — e.g., furazolidone and nitrofurazone.
- Sulfa compounds — e.g., sulfamethazine, sulfathiazole and sulfaquinoxaline.
Antibiotics are used regularly in animal feed at a rate of 2 to 50 grams per ton for improved performance and lower morbidity rate. Levels are often increased to 50–200 grams/ton or more when specific diseases are being targeted — as when the spread of a particular disease is rampant.
Benefits of antibiotic use in animal feeds
- Increasing efficiency and growth rate.
- Treating clinically sick animals.
- Preventing or reducing the incidence of infectious disease.
Antibiotics in animal feed, in general, are used more regularly for increased efficiency and growth rate than to combat specific diseases.
Risks of antibiotics in animal feed
After animals have been fed with antibiotics over a period of time, they retain strains of bacteria that are resistant to antibiotics. These bacteria proliferate in the animal, and through ingestion, the resistant bacteria are transmitted to other animals. Transfer to humans is possible through exposure at farms and slaughterhouses. Multiple human infections could potentially produce a "supergerm" resistant to many drugs due to resistance sharing.
13Carbon tetrachloride poisoning
Carbon tetrachloride (tetrachloromethane) is a halogenated hydrocarbon — a non-inflammable, colourless liquid with a sweet smell. Its chemical formula is CCl₄.
Uses
Carbon tetrachloride is used in the manufacture of fluorocarbon propellants (freon), cleaning and degreasing agents, grain fumigants to kill insects, dry-cleaning solvents, fire extinguishers, and is used widely in some countries to treat sheep infested with liver fluke.
Poisoning
The usual fatal dose for most hydrogenated hydrocarbons is about 4 to 5 mL (20 to 25 mL for a few others). Carbon tetrachloride is one of the most potent hepatotoxins — so much so that it is widely used in scientific research to evaluate hepatoprotective agents. CCl₄ is toxic to the liver and kidney, and is also proven to cause cancer in animals. The severity of the effect depends on species susceptibility, route and mode of exposure, diet, or co-exposure to other compounds — in particular ethanol. Pretreatment with Vitamin E reduces the hepatotoxicity of CCl₄.
Toxicokinetics
The usual route of exposure is either by inhalation or ingestion. Once ingested or inhaled, CCl₄ is distributed throughout the body with highest concentration in the liver, kidney, brain, muscle fat and blood. The metabolism of carbon tetrachloride leads to the formation of trichloromethyl radicals which poison cytochrome P450. The trichloromethyl radical may alternatively react with oxygen to form phosgene. This may play a significant role in mediating carbon tetrachloride hepatotoxicity.
Adverse/toxic effects
Acute poisoning: Exposure to high concentrations of carbon tetrachloride can affect the CNS and degenerate the liver and kidney. Affected persons present with one or more of the following: vomiting, diarrhoea, abdominal pain, headache, lethargy, vertigo, fatigue, altered mental status, delirium, amnesia, and incoherent speech.
Chronic poisoning: Chronic exposure can cause liver and kidney damage and could result in liver and renal cancers. Presentations include several forms listed in acute poisoning and, more, a possible myasthenic reaction — a defect in neuromuscular transmission including symptoms of organ damage (CNS, liver and kidney).
Diagnosis
- Characteristic odour in the breath.
- Isonitrile test — a positive result is indicated by development of a foul skunk-like odour due to formation of phenyl isonitrile.
- Carbon tetrachloride blood levels in actually poisoned patients range from 0.1 to 31.5 mg/L; 2 to 5 mg/dL are generally considered toxic blood levels.
- Hepatorenal toxicity is indicated by abnormal liver function tests — elevated serum hepatic aminotransferases.
Treatment
- Decontamination: Dermal exposure should be washed copiously with soap and water; eye exposure irrigated; and activated charcoal administered after toxic ingestion.
- Oxygen should be administered in altered mental status or respiratory failure.
- N-acetylcysteine given within 8 to 10 hours after exposure has been reported to prevent hepatic damage from acute poisoning by CCl₄ in humans. Alternatively, the Prescott protocol can be followed involving gastric lavage before infusion of N-acetylcysteine.
14Phenothiazine poisoning
Phenothiazines are a class of antipsychotic drugs (classical neuroleptics/major tranquillizers) that have salutary therapeutic effects in psychoses. Phenothiazine is also used to treat infections with parasitic worms (anthelmintic) in livestock. It is effective against a broad range of parasites in cattle, horses, poultry, sheep and swine. It is a highly toxic drug — not recommended for use in humans and not effective in dogs and cats.
In veterinary medicine, the most commonly used phenothiazines are acepromazine, chlorpromazine and promazine. It causes skin irritation in rabbits and guinea pigs.
Clinical uses
Phenothiazines are widely used as antipsychotics (chlorpromazine) and anthelmintics (worming agents) in veterinary medicine.
Mode/mechanism of action
All antipsychotics (except clozapine-like atypical ones) have potent dopamine D₂ receptor blocking action. Phenothiazines also block D₁, D₃ and D₄ receptors, but there is no correlation of such blockade with their antipsychotic potency. Phenothiazines post-synaptically block dopaminergic receptor sites, inhibit oxidative phosphorylation, and decrease the excitability of neuronal membranes. They possess significant anticholinergic, alpha-adrenergic blocking, quinidine-like and extrapyramidal effects. Phenothiazines lower the seizure threshold, hence large doses may produce seizures.
Toxicokinetics
All dopamine receptor antagonists are generally well absorbed on oral or parenteral administration. They are highly lipophilic and protein-bound, accumulating in fat, lungs and brain. Metabolism is largely hepatic and occurs through conjugation with glucuronic acid, hydroxylation, oxidation, demethylation and sulfoxide formation by cytochrome P450 (CYP) 2D6 and CYP3A isoenzymes.
Adverse/toxic effects
Neurological
- Neuroleptic Malignant Syndrome (NMS) — a severe form of extrapyramidal reaction characterized by hyperthermia (39°C to 42°C), marked rigidity, immobility and tremor.
- Acute Extrapyramidal Syndrome — results from decreased dopamine activity in the basal ganglia; onset soon after initiation of phenothiazine therapy, but disappears once the drug is discontinued. Manifestations include akathisia (restlessness), acute dystonia (spasm of jaw and throat, torticollis), and parkinsonism (tremor).
- Chronic Extrapyramidal Syndrome — includes tardive dyskinesia (most serious side effect of long-term phenothiazine; characterized by involuntary facial and limb movements such as constant chewing and lip licking) and rabbit syndrome (rhythmic involuntary movements of the oral and masticatory musculature mimicking a rabbit's chewing; may be irreversible).
Cardiovascular
Postural hypotension, cardiac arrhythmias and ECG anomalies.
Gastrointestinal
Dry mouth, constipation, vomiting and diarrhoea.
Treatment of phenothiazine poisoning
- Ipecac administration has been known to be effective.
- Lavage is also effective even long after ingestion because the atropine-like effect of phenothiazine delays gastric emptying, and phenothiazine is water-soluble and slowly absorbed from the GIT.
- Overdose: Physostigmine is used in the treatment of drugs with anticholinergic activity such as phenothiazine.
15Toxic plants in everyday life
Toxic plants (or poisonous plants) are those that produce toxins which deter herbivores from consuming them. Some plants have physical defences — thorns, spines and prickles — but by far the most common type of protection is chemical.
Many plants commonly used as food possess toxic parts, or are toxic at certain stages of their lives unless processed. Some only pose a serious threat to certain animals (such as dogs, cats or other livestock) or certain types of people.
Understanding the conditions under which plants are most harmful — and avoiding grazing pastures when plants are most toxic — reduces the risk to livestock. Pastures should not be grazed for 3 weeks after applying herbicides when poisonous species are present.
Notable examples
| Plant | Botanical name | Toxic agent | Effect |
|---|---|---|---|
| Apple | Malus domestica | Amygdalin (cyanogenic glycoside) | Seeds mildly poisonous |
| Asparagus | Asparagus officinalis | Furostanol and spirostanol saponins | Berries poisonous; 5–7 ripe berries cause abdominal pain and vomiting; young shoots cause mild skin reaction |
| Cassava | Manihot esculenta | Linamarin and lotaustralin | 40 mg pure cassava cyanogenic glycoside can kill a cow; chronic pancreatitis, goitre, tropical neuropathy in humans |
| Cherry | Prunus cerasus | Amygdalin | Leaves and seeds toxic (peach, plum, almond, apricot similar) |
| Grape | Vitis spp. | Mechanism not fully understood | Potentially toxic to dogs |
| Indian pea | Lathyrus sativus | ODAP (neurotoxic amino acid) | Wasting and paralysis if eaten over a long period |
| Kidney/common bean | Phaseolus vulgaris | Phytohaemagglutinin (lectin) | 4–5 raw beans can trigger nausea, vomiting, diarrhoea; deactivated by soaking or cooking |
| Lima/butter bean | Phaseolus lunatus | Linamarin (cyanogenic glycoside) | Raw beans contain dangerous amounts |
| Lemon | Citrus limon | Aromatic oils, psoralen compounds | Toxic to dogs, cats and some animals; vomiting, diarrhoea, depression, photosensitivity |
| Mango tree | Mangifera indica | Urushiol | Peel and sap can cause dermatitis in susceptible people |
| Nutmeg | Myristica fragrans | Myristicin (natural insecticide/ascaricide) | At high doses, memory disturbance and hallucinogenic effects |
| Onions & garlic | Allium spp. | Thiosulphate | High doses toxic to dogs, cats and some livestock |
| Potato | Solanum tuberosum | Glycoalkaloids — solanine, chaconine | Toxic compounds present in green parts |
| Rhubarb | Rheum rhaponticum | Oxalic acid | Leaves are nephrotoxic |
| Tomatoes | Solanum lycopersicum | Solanine | Leaves and stems cause digestive upset and nervous excitement; can be toxic to dogs |
16Prevention is the most effective strategy
Animal feed, including herbage, may be contaminated with organic and inorganic compounds. Organic chemicals comprise the largest group and include plant toxins, mycotoxins, antibiotics, prion proteins and pesticides. Inorganic compounds include heavy metals and radionuclides. Particulates such as weed seeds and certain bacterial pathogens are common contaminants of feed.
The effects of feed contaminants and toxins range from reduced intake to reproductive dysfunction and increased incidence of bacterial diseases. Residues transferred to edible animal products represent another reason for concern. Several legislations are in place for the control of these chemical compounds and pathogens in feed. However, in many developing countries — particularly in Africa — statutory control of contaminants is at best rudimentary. The scope for decontamination is limited and generally uneconomic.
Prevention — clean sourcing, correct storage, heat treatment where appropriate, and rigorous feed-mill hygiene — remains the most effective and most practical strategy for controlling feed contaminants and toxins.
17Authoritative resources
For important regulatory, veterinary or public-health questions, readers should consult authoritative sources in addition to the information on this page.
18About this guide
This guide is an educational compilation for pharmacy students, veterinary learners and general readers. It does not replace institutional teaching, professional formularies, official regulatory guidance or consultation with a qualified veterinary or medical professional.
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