Steamboat Springs There’s a killer lurking in the rangelands of Northwest Colorado that takes the lives of more livestock in the Western U.S. than any other plant or predator.
It’s called larkspur, a poisonous plant with two common varieties in our corner of the state: low larkspur and tall larkspur. The toxic principal for all larkspurs is the same — an alkaloid or a combination of alkaloids. In our area, alkaloid concentrations in larkspur vary from location to location, from year to year and from species to species. They also vary during the growing season.
Although cattle that consume larkspur in small quantities may only become sick, eating large amounts will kill them. In sufficient quantities, the alkaloids cause neuro-muscular paralysis that leads to respiratory failure, bloat and often death.
Generally speaking, larkspur toxicity is highest when plants first emerge and slowly drops throughout time as the plant matures. However, larkspur is not generally palatable when it’s in the pre-bud stage, and most fatal poisonings occur when the plant is blooming. Larkspur’s palatability increases as the plant matures. The highest risk to cattle death from larkspur is when the plant is blooming — a period of time known as the toxic window.
There’s no proven treatment for larkspur poisoning.
It has been suggested that poisoned animals be treated with cholinergic drugs such as physostigmine. Although such treatment can reverse some of the clinical changes, their influence on larkspur’s lethal effects is unproven. It may be that the stress and excitement of treatment outweigh any beneficial therapeutic efforts.
Currently, conservative therapy, such as placing an affected animal on its brisket or chest with its head uphill to reduce bloating, and the treatment of bloat, are recommended. Most important is to avoid unduly exciting affected animals until they can clear the larkspur toxins from their systems.
There are two species of tall larkspur here. They’re referred to by their scientific names of Delphinium barbeyi and Delphinium occidentale.
Recent research from the USDA Poison Plant Lab in Utah has shown that in Northwest Colorado, D. barbeyi is highly toxic and D. occidentalli is lowly or non-toxic.
This is new information and may explain why ranchers don’t experience livestock deaths on some tall larkspur-infested rangelands.
With a little training you can learn to tell the two species apart, though the differences are minute and one needs to look at flower color and hairiness of the stems to differentiate. The Poison Plant Lab will take samples of a given larkspur patch to let ranchers know its toxicity and risk to livestock.
There are many herbicides that can control larkspur. However, landowners must be careful when using herbicides such as 2,4D when treating larkspur, as many herbicides increase plant palatability and may cause cattle to consume it, inadvertently causing death. Larkspur generally is not toxic to sheep or horses.
There’s a lot more about larkspur than can be relayed in this report.
If you want more information, call me at 970-879-0825. The information in this article comes primarily from the USDA Poison Plant Lab in Logan, Utah.