Lead poisoning perennial problem in cattle

two cows with Goodale Farm in background

Beef cattle at the WCVM's Goodale Research Farm. Photo: Michael Raine.

Every year, Dr. Barry Blakley watches the number of confirmed bovine lead poisoning cases spike during the months of May and August — peak times for seeding and harvesting on the Prairies.

“About two days after farmers start seeding, we see a jump in the number of lead poisoning cases,” says Blakley, a toxicologist at the Western College of Veterinary Medicine (WCVM).

On average, the WCVM-based toxicology lab for Prairie Diagnostic Services (Saskatchewan’s provincial veterinary laboratory) sees about 50 to 60 lead poisoning cases in cattle herds each year. Sixty per cent of those cases coincide with the most hectic times on Prairie farms.

“When farmers are busy with spring and fall work, they may forget and leave their used batteries hanging around without properly storing them. Cows are attracted to used batteries because of the salty taste: they’ll lick it, chew it and even eat the whole battery,” explains Blakley.

It just takes one battery to kill one or more animals and cause clinical signs of poisoning to appear in additional cows. As well, some herdmates may have higher lead levels in their blood and still not show any clinical signs. These asymptomatic animals pose a serious food safety issue that often goes undetected.

Lead poisoning in cattle herds causes economic loss, animal suffering and food safety concerns — plus it can be a major blow to a producer’s breeding program. What’s frustrating for veterinarians and producers alike is that lead poisoning in cattle is completely preventable.

“It’s a farm management problem that can be prevented by the proper disposal of used batteries,” says Blakley. “Part of the challenge is that every producer doesn’t think it’s a problem that will affect them. But if they don’t think about it and let their farm management practices slide during busy periods, they could eventually run into a problem in their own herd.”

What can veterinarians do to help? As Blakley stresses, practitioners can talk about the problem and not assume that all producers and their employees are aware of the risks.

“If you can spend a few minutes pointing out the dangers of leaving used batteries out in the open or allowing cattle to graze around old machinery and abandoned buildings, it could be enough to prevent an accident from happening.”

Here are some frequently asked questions about lead poisoning that may come up during your visits with clients this spring. Blakley, who has authored or co-authored several research papers on the topic, has provided responses to the questions as a starting point for those important conversations.

Q. How much lead is poisonous for a cow?

Depending on the cow’s age and size, somewhere between 400 and 800 milligrams of lead per kilogram is necessary for an acute poisoning. In chronic poisoning cases, cows can slowly poison themselves if they’re licking or eating small amounts of lead-based paint, old tarpaper or shingles every day.

When we test blood or tissue samples for lead, anything above .1 parts per million (ppm) is considered lead exposure. More than .35 ppm is considered acute lead poisoning.

Q. Why are cattle more susceptible to lead poisoning than other livestock?

Cows are more apt to lick or chew on discarded equipment than other animals such as horses. It’s just part of their nature. Plus, cows have a reticulum — a compartment-like structure in their stomach that acts as a trap for ingested foreign objects. Parts of a battery can get lodged in the reticulum where they slowly dissolve instead of passing through the cow’s body.

Q. What are the clinical signs of lead poisoning?  

One or more sudden deaths in a herd could indicate lead poisoning. In live cows, the clinical signs include blindness, convulsions, depression or hyperactiveness. Lead salts irritating the cow’s stomach lining may also cause an inactive rumen.

Q. How does a veterinarian confirm lead poisoning? 

If the animal is already dead, the practitioner can send in the cow’s liver and kidney to a laboratory for lead analysis. We also do the same analysis using blood samples from live animals. We analyze the samples using inductively coupled plasma mass spectroscopy (ICPMS) that allows us to simultaneously measure about 20 different metals at one time. Each element emits a very specific wave length at a certain place, so if we see a spike, we know there’s excess lead in the sample.

Q. Why is it important to confirm a diagnosis of lead poisoning?

It’s important to know the cause of death so you can prevent future deaths or disease. If tests do confirm that it’s lead poisoning, you can make sure to search for and remove the lead source out in the pasture or in the yard.

Q. Are there are other conditions that have similar clinical signs?

Yes, there’s a whole list of differential diagnoses including polioencephalomalacia, rabies, insecticide poisoning, BSE, bacterial infections, or ingestion of a poisonous plant or cyanide. Anything causing nervous signs could be mistaken for lead poisoning.

Q. Can cows with clinical signs of lead poisoning be treated?  

Calcium disodium edetate (Ca-EDTA) and thiamine are chelating substances that reduce the levels of lead in affected cattle. But because lead residues in food-producing animals are a food safety risk, the WCVM’s recommendation is to slaughter and properly dispose of carcasses so they don’t enter the human food chain or cause lead poisoning in other species like coyotes, eagles and wild animals.

Q. What’s the main source of lead that causes poisoning in cows?

Batteries account for 90 per cent of the poisoning cases. The other 10 per cent of cases are caused by the ingestion of old shingles, paint or tarpaper. All of those products — including crankcase oil — used to contain high levels of lead.

Q. Does lead poisoning affect other animals?

Cattle account for about 95 per cent of the cases we see while other cases involve wildlife (wild birds, coyotes or wolves eating contaminated carcasses that weren’t disposed of properly). We also see some cases involving dogs that have ingested a lead toy or found old supplies of lead-based paint.

Q. What can producers do to prevent lead poisoning?

  • Contact your province’s recycling program, find the nearest depot that accepts used batteries and follow proper disposal methods.
  • Don’t bury used batteries since the soil will eventually erode and expose the old batteries. Plus, lead seepage can potentially contaminate soil and water.
  • Don’t allow cattle to graze in areas containing machinery or abandoned buildings. Ensure that pastures are clear of junk before putting your cows out to graze.

Q. In most cases of lead poisoning, only a small number of cattle are affected. What’s the big deal? 

Prevention is important because lead poisoning affects a lot of areas in society: the cattle industry, animal health, public health and food safety. If a cow with high lead levels in its blood enters the food chain (milk or meat), lead is a serious health risk for humans — especially children.

As well, it’s not just cows that die or show clinical signs of lead poisoning that have high lead levels in their blood. Nearly 10 years ago, I was part of a WCVM-based research project* that collected blood samples from three herds of cattle that had been accidentally exposed to discarded batteries. After analysis, we found that between four and 12 per cent of asymptomatic cattle in all three groups had blood lead concentrations consistent with acute lead poisoning (more than .35 ppm).

Our recommendation: if you have lead poisoning in your herd, you need to monitor every animal to confirm that they haven’t been exposed to lead even if they’re not showing clinical signs. As the research shows, there is a potential food safety risk for all of us.

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*Waldner C, Checkley S, Blakley B, Pollock C, Mitchell B. 2002. “Managing lead exposure and toxicity in cow-calf herd to minimize the potential for food residues.” Journal of Veterinary Diagnostic Investigation. 14:481-486.

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