Why did the moose drink the water? Death at a prairie dugout.

In late September of 2020, three moose were reported dead in a dugout in rural Saskatchewan. The moose had been seen alive in the area two days prior by the renter of the land. Local conservation officers from Saskatchewan Ministry of Environment Humboldt field office investigated the scene and did not find any signs of bullet wounds or other obvious cause of death. The investigating officers managed to pull the carcasses of an adult male and juvenile female from the water to be transported to the lab at CWHC Western/Northern, leaving one adult female behind, whose carcass was in poor condition. A water sample was also collected from the dugout and submitted for testing.

Back at the lab, thorough postmortem investigations were carried out on both carcasses. The adult male was in good body condition, which suggests a relatively short illness or sudden death. Gunshot was ruled out and tests were performed to rule out other common causes of sudden death, including lead poisoning, insecticide poisoning, and anthrax. Both animals were found to have toxic, life threatening levels of sodium in the brain. This is an indicator of severe dehydration which can lead to shock and death.

The water sample from the dugout had also been sent out for a water quality assessment, with the hope that the results would shed some light on the circumstances. The results showed several issues with the water source, including extremely high levels of sulfur, sodium, chloride, and sulphate. Although acceptable levels for moose are not available, the levels found in the submitted water sample were above the range noted to cause dangerous health issues in cattle. As well, high levels of sulphate can have an additive effect with sodium chloride, so extremely high levels of both would be particularly harmful, and can cause sudden death in animals with no other water source. An example of this was seen in 2017 in a different area of Saskatchewan, when 200 cattle died after exposure to a water source with extremely high sulfate levels. In these situations cattle would likely refuse to drink the water, but would eventually drink it out of necessity and succumb to dehydration caused by salt toxicity. Fortunately the dugout in the moose case was recently dug and had not yet been used as a water source for cattle.

Although the water quality seems a likely explanation for the death of these three moose, we were left with one big question: Why would they drink the water? The weather was unseasonably warm in late September (>20^oC during the days of the incident) and the moose would have had significant water requirements (20-50 L/day). Unlike cattle, however, moose would be free to roam in search of other water sources as needed. As in many wildlife health investigations, we may never know all the details surrounding the incident and are sometimes left with more questions than answers; however, the incident allowed us to alert the landowner about the unsuitability of the dugout for livestock.

This is a great example of the many moving parts involved in a wildlife health investigation. CWHC Western/Northern relies on the hard work of the SK Ministry of Environment Conservation Officers who respond to reports from the public, conduct the initial investigation, and transport carcasses and samples to the CWHC for further testing. Hauling an 800 lbs bull moose out of a dugout is no easy feat and we appreciate all the work that went into this case.

Submitted by:

Erin Moffatt

CWHC Western/Northern region