Exposure to lead

Livestock may be exposed to lead from a variety of environmental and on-farm sources.

Exposure to lead poses a significant health risk to both animals and humans. Ingestion of lead can result in serious, lifelong health effects and may be fatal.

Products derived from animals with elevated lead levels may present a risk to human health and will not be permitted to enter the food chain. Lead levels are considered elevated when detected at 0.10 ppm in blood or ≥ 35 ppm in liver or kidney.

Lead storage in the body

Lead, once ingested, dissolves in the digestive tract, is absorbed into the blood stream and then moves through the body to soft tissues, including the nervous system.

Over time, lead moves into bone and may continue to move back and forth between bone and soft tissue.

At any time, lead may be present in multiple tissues in the same animal in different concentrations, which leads to some of the variability in animals with chronic exposure, which may test positive for years.

Lead sources

Cattle are commonly affected by lead exposure due to their naturally curious behaviour and tendency to investigate and consume unfamiliar objects.

The most common source of lead exposure in livestock is grazing contaminated pastures, although feed can also be contaminated. For example, an improperly discarded lead battery may be accidentally incorporated into silage during harvest and fed to multiple animals.

Potential sources of lead exposure include:

  • discarded vehicles, farm machinery, and their associated components, such as:
    • batteries, particularly when the plastic casing is damaged or deteriorated, exposing lead plates or lead compounds. Prolonged exposure to environmental conditions, including freeze-thaw cycles, can cause battery casings to crack, making components more easily accessible to livestock and releasing lead into the surrounding area.
    • leaded gasoline, waste oil and used oil filters from older equipment
    • grease and lubricants that may contain lead contaminants
  • lead-containing tanks, pipes or plumbing fixtures with lead solder
  • lead-based paints, particularly on older buildings, fences, equipment and structures where paint deterioration may occur
  • ammunition and fishing tackle, including lead shot, bullets and fishing weights
  • contaminated feed, feed ingredients, mineral supplements or water sources
  • contaminated soil, including soils affected by industrial activities, improper waste disposal or naturally elevated lead concentrations

In breeding livestock, lead toxicosis can adversely affect reproductive performance, and may result in infertility, pregnancy loss or premature birth. Offspring born to lead exposed dams may be exposed to lead in utero and can be affected by lead toxicosis after birth. In addition, lead can be excreted into milk, creating a potential source of exposure for nursing youngstock.

To protect food safety and public health, lead shot should not be used to euthanize livestock intended for human consumption, as residual lead in tissues may pose a risk to consumers.

Clinical signs

The onset and severity of clinical signs of lead toxicosis can vary depending on the source and amount of lead ingested, the duration of exposure and the animal’s physiological status.

Common clinical signs include:

  • diarrhea
  • incoordination or staggering
  • blindness
  • recumbency (inability to stand)
  • muscle tremors
  • abnormal behaviour such as isolation from the herd

In cases of severe exposure, lead toxicosis may result in:

  • convulsions or seizures
  • coma
  • death

In some instances, sudden death in an otherwise healthy animal may be the only observable indication of lead exposure.

Animals exposed to low levels of lead over an extended period may not exhibit obvious clinical signs. In ruminants, small lead fragments can remain in the reticulum or rumen for months or even years without causing overt disease because of the relatively stable rumen environment. Physiological stressors, such as ruminal acidosis or concurrent illness, may precipitate the onset of clinical disease by mobilizing lead. Producers should consult a veterinarian immediately if livestock exhibit neurological signs or if unexplained sudden deaths occur.

Animals with elevated blood lead concentrations may not display clinical signs and can appear healthy. Despite the absence of observable illness, products derived from these animals may contain lead residues that pose a risk to human health and may be deemed unsuitable for human consumption. When lead toxicosis is diagnosed, other livestock on the farm with a similar risk for exposure must also be evaluated.

Suspicion or diagnosis of lead toxicosis

If lead toxicosis is suspected in livestock, producers should contact their veterinarian immediately.

Under Ontario's Animal Health Act, 2009, veterinarians must report incidents that pose a significant risk to animal health, public health or food safety. This includes suspected or confirmed cases of lead toxicosis. Lead toxicosis is an immediately notifiable hazard in Ontario and Ontario laboratories are required to report test positive results to the Office of the Chief Veterinarian for Ontario at the Ministry of Agriculture, Food and Agribusiness (OMAFA).

If lead toxicosis is suspected, the following actions should be taken immediately:

  • Do not transport any potentially exposed animals off the premises.
  • Do not permit affected animals or animal products, including milk, to enter the food chain.
  • Do not feed carcasses of affected animals to other animals, such as dogs, and take measures to prevent wildlife from accessing carcasses to avoid secondary poisoning.
  • Prohibit further access to any suspected source of lead.
  • Contact your veterinarian or an OMAFA veterinarian through the Agricultural Information Contact Centre at 1-877-424-1300 or ag.info.omafra@ontario.ca.

A diagnosis of lead toxicosis can be confirmed by a veterinarian through laboratory analysis of blood samples collected from live animals or liver, kidney or muscle samples collected from deceased animals. When elevated lead concentrations are detected or suspected in livestock intended for human consumption, affected animals will be required to remain on the premises until laboratory testing confirms that lead concentrations are below established food safety thresholds. The costs associated with testing are the responsibility of the livestock owner.

When an obvious source of lead exposure cannot be identified, investigate feed, water and soil as potential sources of contamination. Laboratory testing may help determine the origin of exposure and guide corrective actions.

There is no approved treatment for lead toxicosis in food-producing animals. However, veterinarians may be able to provide supportive care to help manage clinical signs and improve animal welfare.

Prevention

Check for potential lead sources

Inspect pastures and livestock accessible areas before turnout for potential sources of lead contamination. Remove and properly dispose of any materials containing lead. During periods of drought or reduced pasture cover, discarded lead-containing objects may become more accessible to grazing livestock and increase the risk of exposure.

Maintain fencing and exclusion barriers to prevent livestock from accessing known or potential sources of lead contamination such as old vehicles, farm machinery, waste disposal areas or abandoned buildings.

Regularly inspect batteries used to power electric fences, water pumps or other equipment to ensure they remain intact and are stored in a manner that prevents livestock access.

Evaluate watering and feeding equipment for components that may contain lead. Replace any lead-bearing materials that could come into contact with feed or water. Where the presence of lead is uncertain, commercially available lead test kits may be used to assess potential risks.

Disposal

Dispose of lead-acid batteries responsibly through approved household hazardous waste depots or community recycling centres that accept automotive batteries. Local automotive shops may also be able to facilitate safely disposing of a battery. Proper disposal helps prevent environmental contamination and reduces the risk of exposure to livestock, wildlife and other animals. Producers should consult their local municipality regarding available recycling and disposal programs.

Appropriately dispose of animals that have died from lead toxicosis to prevent scavenging by farm dogs, coyotes, birds of prey and other wildlife. Improper carcass disposal can result in secondary lead poisoning and contribute to the spread of environmental contamination.

Lead toxicity in other species

Although cattle are the livestock species most affected by lead exposure, lead toxicosis can occur in a wide range of domestic and wild animals.

Backyard poultry may be exposed through contaminated soil or access to discarded lead-containing materials within their environment. Chickens exposed to lead may accumulate lead residues in their tissues and eggs, potentially posing a risk to human health. Consequently, eggs and meat from affected birds should not be consumed until appropriate veterinary and regulatory guidance has been obtained.

Other species susceptible to lead toxicosis include:

  • sheep
  • goats
  • horses
  • companion animals such as dogs and cats
  • domestic birds

Pet birds, including parrots, are particularly vulnerable due to their tendency to chew and explore their environment. Common sources of exposure in companion birds include lead-containing toys, surfaces coated with lead-based paint, and household items such as older window blinds and other lead-containing fixtures.

Clinical signs of lead toxicosis in these species are generally similar to those observed in livestock and may include neurological, gastrointestinal and behavioural abnormalities. Anyone who suspects lead toxicosis in an animal should seek veterinary care immediately.

In companion animals, chelation therapy may be an option to reduce lead levels and improve outcomes. However, treatment is most effective when initiated promptly following exposure. Home remedies, such as charcoal, are generally not effective for lead toxicosis and may result in delaying proper treatment.

If wildlife exposure is suspected, such as the discovery of dead or neurologically impaired raptors, waterfowl, particularly swans and loons, coyotes, foxes or other wildlife species, concerns should be reported to the Canadian Wildlife Health Cooperative (CWHC). The CWHC can facilitate diagnostic testing and surveillance activities to help identify and monitor cases of wildlife lead poisoning. Do not handle neurologically abnormal wildlife as they may pose a risk to human health.