Old garbage dumps litter the Prairies. Through the generations many things were dumped and forgotten by Prairie residents. Unfortunately, some of those things included old batteries, containers of used oil from the days of lead-based gas additives, lead-based paint and elemental lead. Few appreciate lead’s tenacity as an environmental contaminate. A used car battery buried in a blow-dirt ridge, for instance, is still highly toxic when exposed by erosion 50 years later.
The lead-acid battery was invented in 1859 and though more highly refined today it remains an automotive standard. Approximately 60 per cent of a battery’s weight is composed of lead and lead oxide. In North America between 2.6 and three million tonnes of lead are used in batteries every year. Today a high percentage of lead is recycled, but for many years thousands of tonnes of this heavy metal were carelessly discarded in private dumpsites that through the years were unwittingly incorporated into cultivated fields and pastures and ultimately became a source of lead poisoning for cattle, sheep and horses.
Lead exposure in food animals is a potential food safety issue. There is a growing body of evidence suggesting there is no safe level of lead in humans, especially children. Research studies have shown a link between low-level lead exposure and lower IQs. Even very low levels of lead in the blood — previously believed to be safe — could be a contributing factor in developmental abnormalities like attention deficit hyperactivity disorder. In another study, blood lead levels below existing U. S. Center of Disease Control’s established “safe” thresholds for public health action were associated with adverse educational outcomes in children.
Canada, the U. S., Great Britain and Australia all report lead exposure as the most common cause of cattle poisoning. Lead poisoning can affect any cattle operation and often involves animals from well-managed farms and ranches. Sometimes only a single calf may be involved, at other times 20 or more cattle may be lost in a single poisoning incident.
One animal showing clinical signs often signals exposure and potential poisoning in other animals. Cattle readily drink crankcase oil, lick grease from machinery, lick paint and chew on exposed plates of a deteriorating lead battery. Ingested lead settles in the fore stomachs of cattle where digestive acids gradually change lead into poisonous salts, which are absorbed and widely distributed in an animal’s body.
More than 85 per cent of lead poisoning incidents among cattle in Alberta result from accidental consumption of discarded materials from farm vehicles or machinery. Garbage dumps remain the most common source of poisonous materials. Over the years, other sources have included crop sprays, putty, lead-based paints and painted surfaces, roofing materials, plumbing supplies, asphalt, lead shot, linoleum and oilfield waste. Boiled linseed oil, which contains lead, may poison livestock when used as a laxative.
Lead’s effect on red blood cells and bone marrow causes anemia. Small blood vessels are damaged, resulting in bleeding and oxygen deprivation to nerves, brain tissue and a variety of other organs. Lead severely damages kidney and liver cells and can cause sterility, fetal death and abortion. Lead poisoning is common among calves because of their inquisitive feeding habits and the fact that lead is more readily absorbed from the gastrointestinal tract of younger animals.
Lead poisoning is most common in the spring when animals are turned out to pasture. In one Alberta incident, 30 adult beef cattle died when a discarded tractor battery, left in a field, was accidentally chopped into corn silage. There are many reports of cattle poisoned after eating soil on which used motor oil had been spilled. Heavy rain during the spring and summer of 2010 exposed a number of old dumpsites containing things like discarded batteries.
Although clinical signs of poisoning normally precede death, most animals are simply found down or dead on pasture. Clinical symptoms usually develop quickly after exposure, but may take a week or more. The first signs are often depression, loss of appetite, diarrhea. Nervous signs if observed before death include teeth grinding, twitching of eyes and ears, head bobbing, circling, head pressing, staggering, muscle tremors and blindness. Death usually results from respiratory failure during convulsions or can be associated with misadventure like drowning when blind animals wander into ponds and dugouts. Animals often die in 12 to 24 hours after clinical signs are first noticed. Elevated lead levels in blood, kidney and liver are used to confirm a diagnosis. In many cases, lead is visible in the gastrointestinal tract on post mortem.
A correct diagnosis is extremely important for identifying the problem and preventing further exposure. All too often livestock owners are unaware of the presence of the source of lead. A walk about after a confirmatory diagnosis of lead poisoning invariably turns the “just can’t be” into a “didn’t know the dump was there.”
Managing a herd following cases of lead poisoning can be difficult and very expensive. Determining the level of exposure and the length of time animals need to be safely kept out of the food chain often calls for repeated testing and long delays in marketing. There are some within the food, veterinary and livestock industries that would prefer to never have animals exposed to lead enter the food chain. The best solution is preventing a problem totally created by people.
Be aware of the toxic dumps. Many of them have been in someone’s backyard.
Man.R3H0H1,or [email protected]