Отравление свинцом продолжает убивать телят на пастбищах Канады: источник часто скрыт годами

Lead poisoning is still killing calves on Prairie pasture The source is often a battery no one knew was there By Lexie Reed 3 days ago 5 min read Lead poisoning is the most diagnosed poisoning of Canadian cattle since the 1950s. It is toxic to the brain as well as several other systems within the body. Its toxicity to humans and animals alike is common knowledge. Regulatory changes in lead incorporation in residential and commercial products in the last five decades have greatly reduced the amount of lead present in the modern environment. So why are cattle still dying of lead poisoning? To better understand this issue, Dr. Vanessa Cowan, veterinary toxicologist from the Western College of Veterinary Medicine in Saskatoon, Sask., analyzed lead poisoning diagnostic records in Western Canada from 2014–24. Cowan says that lead poisoning is diagnosed by a combination of clinical signs: a history of lead poisoning in the herd or geographical area, access to lead-containing debris and laboratory diagnostics. Cowan found that on average 23 herds were affected per year, and that most diagnoses were made post-mortem. The most reliable samples to test for lead poisoning are blood, kidney or liver samples from affected animals. Why It Matters Lead poisoning has not gone away with leaded gas and lead paint. Cowan’s review of records from 2014 to 2024 found an average of 23 herds affected each year. Most were diagnosed after the animals were dead and calves are the ones most at risk. Where the lead is coming from Historically, common sources of lead came from gasoline, grease, batteries, paint and industrial waste. Leaded gasoline was banned in Canada in 1990, and lead levels in paint have dropped precipitously since the mid-1970s. Modern sources of lead now come from batteries and old building materials (including paint and shingles). Read Also Research on the Record BCRC survey results guide where check-off research dollars go In cases of lead poisoning in cattle, batteries or old vehicles improperly disposed of in pastures appear to be a significant source of poisoning. The average automotive battery contains 20 pounds (10 kilograms) of lead; the fatal dose for a 1,300-lb. cow is as small as 350 grams, and for a 200-lb. calf as little as 18 g. The most lead poisoning cases were presented to Prairie Diagnostic Services in June, followed by July and May. The year with the most cases submitted was 2018 (36 affected herds), and the fewest was in 2023 (12 affected herds). In future studies, Cowan would like to investigate other factors that may contribute to lead poisoning cases, such as drought. “I speculate that drought years and subsequent low water levels can ‘reveal’ sources of lead that are normally hidden to cattle, like a battery at the bottom of an old pond or dugout,” says Cowan. “Drought and lack of trace minerals may also result in cattle seeking out mineral sources in their environment, which could include chewing on objects they normally wouldn’t.” Why calves are hit hardest Cowan also found that calves (defined as under a year of age) were overwhelmingly affected by lead poisoning, and calves under four months of age were affected more than older calves. “Calves have the ability to fit into places where yearlings and larger cows cannot, so they have greater access to sources of lead,” Cowan explains. FATAL DOSES - One automotive battery holds about 20 lb. (10 kg) of lead. - A fatal dose for a 1,300-lb. cow is about 350 grams. - A fatal dose for a 200-lb. calf is as little as 18 grams. “Calves also absorb more lead from their gastrointestinal tract compared to adults. Young calves have relatively immature blood-brain-barriers as well, making them more vulnerable to neurotoxicants.” What lead poisoning looks like The top clinical signs of lead described in the case histories were blindness, acute death and tremors/seizures. Other clinical signs observed from these cases were salivation and frothing, altered mental status, circling, abnormal chewing or licking motions, wandering and abnormal vocalizing. The source is usually a mystery One of the most interesting findings in Cowan’s analysis of these cases was that most of the histories did not indicate a potential source of lead poisoning. In many circumstances, cattle had been grazing the pasture for years without issue, and the producers did not know of any batteries or other lead sources in the pasture. “Sometimes, the source is hidden for years by water, soil or other materials,” says Cowan. “(In some cases), unexplained deaths on pasture are not investigated, so the source of lead is still present for subsequent grazing years. “Other times, potential sources are known but have been untouched by cattle for years. It’s unclear what changes occur to cause cattle to investigate these old sources.” In 36 cases, batteries were found after the diagnosis of lead poisoning. Other suspected sources were old machinery and scrap metal, old shingles and grazing cattle on an old scrap yard site. Three key patterns arose from the cases in Western Canada that Cowan looked at: pasture access, exposure in the months of May through July, and calves being at highest risk. “The highest-risk period is turnout of cow-calf pairs onto pasture,” says Cowan. Fencing, minerals and investigating deaths Cowan suggests that old farm buildings, equipment and old dump sites or rock piles be fenced off to prevent access, even if cattle have previously left these areas alone. She also advises that cattle have ample access to feed, water and mineral to dissuade them from chewing on potential lead sources. “Consider if previous deaths have occurred on the pasture; if there have been, consider the possibility of a lead source,” Cowan says. “If there is a death on pasture in an otherwise healthy animal, investigate right away. This could save other cattle. Multiple poisonings are typical in herds, and these cases often start with one or two deaths.”