Effects of Rangeland Management on Milkweed Grazing and Monarch Conservation

Cattle typically avoid consuming milkweed plants that contain high levels of toxic defense compounds, and therefore many people assume cattle avoid all milkweeds. However, common milkweed (Asclepias syriaca) contains only moderate levels of toxic compounds, and observations suggest that cattle regularly consume common milkweed and may even preferentially graze flowers and leaves of this species. These observations directly relate to efforts to add over one billion stems of milkweed to the central USA for monarch butterfly (Danaus plexippus) conservation. If cattle intentionally consume common milkweed and other milkweed species, and if certain management practices can reduce milkweed grazing and increase the number of milkweed stems, then rangeland management could have a major impact on milkweed abundance in states like Nebraska where 46% of the land is grazed by domesticated livestock. I completed a study to examine the effects of rangeland management on milkweeds and monarchs in central Nebraska prairies. This study quantifies how often cattle graze milkweed under different patch-burn grazing regimes and the effects this has on milkweed stem density. My results show that milkweed stem density is higher in fields ungrazed by cattle than in grazed fields. In grazed fields, cattle removed more vegetation in areas burned in the current year than those burned in previous years, but milkweed grazing remained constant in all areas, suggesting that cattle were seeking out milkweed even in areas where they spent less time grazing. In a separate study I completed, results suggest that milkweed grazing reduces monarch egg laying