Lead contamination in food-producing animals

Lead exposure can cause serious illness in animals and sometimes causes death. Cattle are the most common food-producing animals affected.

If animals consume lead or lead pieces, or even lick lead surfaces, they may absorb enough of the metal to cause lead poisoning.

At low levels of exposure, they may survive and not show clinical signs of lead poisoning. Even so, there may be unacceptable levels of lead residue in the meat, liver and kidney from those animals, or in milk that they produce. If these residues exceed the maximum level set for lead in the Australia New Zealand Food Standards Code, the product will be unsuitable for human consumption. If you suspect your animals have, or are at risk of, lead poisoning, or may have lead above maximum levels, you must not send them to slaughter.

The Biosecurity Regulation 2016 adopts the contaminant standards for heavy metals included in schedule 19 of the Australia New Zealand food standards code as the acceptable levels for contaminants in plant and animal food commodities.

Under the Biosecurity Act 2014, anyone who deals with biosecurity matter has a general biosecurity obligation to minimise biosecurity risks posed by the matter, especially if these risks may affect human health or trade.

Lead contamination of food-producing animals is a serious risk to human health and trade in agricultural commodities, as the lead may enter the food chain. Therefore, people who deal with food-producing animals that show signs of lead poisoning, or with animals that may be contaminated with lead, must minimise these risks.

Lead contamination is a notifiable incident under the Biosecurity Act 2014. You must notify a Biosecurity Queensland officer if you suspect that food-producing animals are affected by exposure to lead.

This guide contains information about:

major sources of lead
how to safely dispose of toxic rubbish
signs of lead poisoning
clinical testing and treatment advice for veterinarians.

Causes and signs of lead poisoning and contamination in production animals

Animals may find material contaminated with lead in silage, rubbish dumps and around farm buildings and machinery. Lead can be present in:

discarded sump oil and oil filters
lead batteries (the most common cause of cases)
flaking lead-based paint or old paint tins
lead shot and fishing sinkers
linoleum, grease, putty, metallic lead
other sources.

Animals are likely to seek out sweet-tasting lead compounds if they are bored from being confined or have changed appetites from malnutrition or phosphorus deficiency.

The easiest and most effective way to protect your production animals from lead poisoning and contamination is to dispose of lead safely. Never dispose of toxic waste in general rubbish dumps or bins. Local councils usually provide options for toxic waste disposal. Local garages may dispose of sump oil and car batteries for you, and some scrap metal merchants will purchase lead batteries.

If your animal is showing signs of lead poisoning you should:

provide the animal with food, water and shade
keep the animal separate from other animals
try to identify and remove the hazardous material from your property
collect a sample of the hazardous material for analysis
contact your veterinarian.

Signs of lead poisoning in production animals

Symptoms vary according to the degree of poisoning, but animals may show a combination of gastrointestinal and nervous signs. Gastrointestinal signs may include either constipation or diarrhoea.

Acute lead poisoning

In cases of acute lead poisoning, animals may be found dead or they may display combinations of several signs for a few hours before death. These signs may include:

colic
staggering gait
rolling eyes
slobbering
muscle spasms
blindness
uncoordinated attempts to climb obstacles
excessive response to external stimuli
head pressing
convulsions.

Subacute lead poisoning

In cases of subacute lead poisoning, animals may display signs such as:

dullness
loss of appetite
abdominal pain
diarrhoea.

Chronic lead poisoning

In cases of chronic lead poisoning, animals may be found dead or display signs such as:

symptoms of acute poisoning – see above
loss of appetite
wasting
anaemia
constipation
recumbency
difficulty breathing.

Diseases with symptoms similar to lead poisoning

Other diseases that can cause nervous system signs that are similar to lead poisoning include:

tick fever – cerebral babesiosis
nutritional and metabolic deficiencies – hypomagnesaemia, ketosis, thiamine deficiency, vitamin A deficiency
other types of poisoning – mercury, organophosphates, organochlorines
plant poisoning – Noogoora burr, pyrrolizidine alkaloid poisoning
enterotoxaemia – Clostridium perfringens type D
viral infections – infectious bovine rhinotracheitis (IBR), sporadic bovine encephalomyelitis (SBE), and bovine malignant catarrh (BMC)
bacterial infections – listeriosis.

The general biosecurity obligation

If you are dealing with food-producing animals, you are bound by a general biosecurity obligation under the Biosecurity Act 2014. This obliges you to minimise the risk posed by conditions such as lead poisoning and contamination in your animals. Fulfilling the obligation includes correctly disposing of waste materials that contain lead, and ensuring that food-producing animals that come into contact with lead are dealt with appropriately.

Clinical testing and treatment advice for vets responding to lead poisoning

In cases of suspected lead poisoning, samples that should be submitted for analysis – where possible – include:

suspected sources of lead
clotted blood and faeces from live animals
unpreserved liver and kidney from dead animals
preserved liver or kidney
blood samples containing ethylenediaminetetraacetic acid (EDTA) and a blood smear – may also assist with differential diagnosis.

Clinical lead poisoning in adult ruminant animals is associated with lead levels of more than 10mg/kg in liver or kidney, but fatal poisoning can occur with lower tissue levels.

The Australia New Zealand Food Standards Code sets maximum levels for lead:

in edible offal of cattle, sheep, pig and poultry at 0.5mg/kg
in meat (excluding offal) at 0.1mg/kg.

For cattle, a normal blood level of less than 0.24µmol/L (less than 0.05mg/kg) has been adopted across Australia to assist in determining if lead residue levels could pose a food safety risk.

Treating lead poisoning

Treatment of animals with lead poisoning may not be successful if the animals have extensive tissue damage, especially if the damage is in the nervous system.

Animals receiving treatment must be under the care of a veterinary surgeon and treatment may take several days. Animals are usually treated with an intravenous injection of calcium versenate as a chelating agent.

It is important to provide supportive therapy, including fluids and sedatives, to combat convulsions.

Managing food-producing animals containing unacceptable levels of lead

Cattle with elevated blood levels of lead and untested animals in exposed herds or mobs must be excluded from slaughter to ensure that there is no food safety or trade risk from food products derived from exposed animals.

Detained livestock must be permanently identified with an approved device, such as a National Livestock Identification System (NLIS) device. These animals are assigned a residue status to alert processing establishments about potential contamination issues

Contact the Customer Service Centre for a copy of the policy for managing food-producing animals that have been diagnosed with lead poisoning, have elevated blood lead levels or have been at risk of exposure to a lead source. A biosecurity officer from the Department of Primary Industries will investigate each case of lead poisoning.