Researchers at the Western College of Veterinary Medicine at the University of Saskatchewan have studied animal poisonings over 16 years and found nearly half were caused by lead and most occurred in the spring and summer.
Vanessa Cowan and Barry Blakely examined records in the Prairie Diagnostic Laboratory database and published their results in the Canadian Veterinary Journal.
They reported 1,341 poisoning cases with 19 different poisons over the study period.
About half were lead poisonings, and about one-third were due to pesticides, such as acetylcholinesterase inhibitors and strychnine. Anti-cholinesterase chemicals are used as insecticides and include organophosphates and carbamates.
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They interfere with an important chemical messenger in the nervous system, resulting in muscle twitching, drooling, diarrhea, vomiting, urination, seizures and death. Cattle, sheep, goats and eagles were commonly poisoned with these chemicals.
The third most common poisoning involved essential metals like copper, selenium, iron and sodium. Copper poisoning occurred in 122 animals, representing nine percent of the overall cases. Arsenic and cyanide poisoning were rare at less than one percent of the total cases.
The researchers found that cattle had the most reported poisoning cases at 696 and most of those were caused by lead.
Lead has been identified in previous studies as the most common poison of cattle stretching back over 40 years. Lead poisoning was most common in July, which fits with the presumed source of exposure. Grazing beef cattle lick and ingest the lead components of lead-acid batteries. It is essential that producers remove sources of lead from pastures because it represents an ongoing food safety concern. Cattle can die from high doses of lead, and animals exposed to non-lethal doses can potentially enter the human food chain.
Other common toxins in cattle were the trace mineral metals selenium, copper and molybdenum. Selenium poisoning can occur when cattle feed is produced in selenium-rich soil. Other potential sources include agricultural pesticide chemicals and injectable selenium solutions.
Copper toxicity in cattle is less common than in sheep but occurs when minerals and rations have mixing errors. Pasture and forage crops in certain soil zones are high in molybdenum.
Among sheep and goats, copper was the most common poison present in nearly two-thirds of cases. Small ruminants are sensitive to high levels of copper in their feed.
Poisoning occurs if they are inadvertently fed cattle rations, which contain higher copper than they can tolerate. Much less frequently, selenium and manganese poisonings were also reported in sheep and goats.
After cattle, dogs were the most frequently poisoned animals. Most were poisoned with strychnine. Strychnine is a rodenticide and is labelled for poisoning gophers in the spring. The study did not identify the source of these 93 dog poisonings, so it is unknown whether dogs were maliciously poisoned or if they ate strychnine bait or poisoned rodents.
Compared to previous studies in the region, some types of poisonings appeared to have decreased over time. For instance, there were fewer cases of mercury poisoning, possibly due to changes to agricultural regulations.
The study only included animals submitted to the diagnostic laboratory, so true rates of animal poisoning in Western Canada could vary. Despite the potential bias, this type of study is critical to assess the current important poisons and to evaluate trends that may affect surveillance, management and veterinary care.
