Plains larkspur (Delphinium geyeri) grazing by cattle in Wyoming

Abstract

Plains larkspur (Delphinium geyeri Greene) is a major cause of cattle deaths in the northern Great Plains of Wyoming and Colorado. We examined the amount and timing of larkspur ingestion by grazing cattle in relation to larkspur phenology, nutrient concentrations, and weather conditions. Four summer grazing trials were conducted near Cheyenne (1996 and 1997) and Laramie, Wyo. (1998 and 1999). All trials began when plains larkspur was vegetative or in the early bud stage. In the first 2 studies, 6 yearling heifers grazed from 3 May to 4 August 1996; the same animals plus 5 cow-calf pairs grazed from 13 May to 10 August 1997. During both 1996 and 1997, cattle ate 0.5 to 1% of bites as larkspur during May, then consumption decreased to nearly 0 during the remainder of both summers. When eaten, larkspur was typically consumed during cool, foggy weather conditions. In the last 2 studies, 6 cow-calf pairs grazed near Laramie, Wyo., from 13 May to 30 June 1998, and 6 different cow-calf pairs grazed from 2 June to 20 July 1999. Cattle ate substantial amounts of plains larkspur (herd average approximately 3%) during the vegetative and bud stages from mid-May into early June, 1998. Cattle may have eaten more larkspur during 1998 because drought reduced spring availability of green grass. Consumption of larkspur was negatively related (r2 = 0.43) to daily temperature in 1998, but not during 1999. During 1999 cattle ate essentially no plains larkspur during the vegetative and bud stages, but ate larkspur (herd average approximately 5%) during the flower and pod stages when larkspur plants were beginning to desiccate and ambient temperatures were above average. This series of trials indicates that it will be difficult to predict plains larkspur consumption based on larkspur growth patterns or weather. Although cattle sometimes increase plains larkspur consumption when temperatures are cooler than normal, this pattern is not consistent enough to serve as a basis for management recommendations.