Nutrient Composition of Spotted Knapweed (Centaurea maculosa)

Abstract

Spotted knapweed (Centaurea maculosa Lam.) is a noxious plant that has invaded many native ranges and open woodlands of western Montana. Knapweed is generally considered to have a low palatability to domestic livestock and wildlife, but local ranchers have observed sheep, goats, and some cattle ingesting large quantities of fresh knapweed during the spring and knapweed silage and hay during the winter. Nutrient analysis of plants collected prior to flowering showed neutral detergent fiber at 24.2 to 53.0% (dry wt.), ether extract 3.1 to 9.0%, crude protein 6.2 to 18.2%, total nonstructural carbohydrates 11.0 to 27.5%, ash 4.9 to 9.3%, in vitro dry matter digestibility 53.2 to 61.8%, and gross energy 4,088 to 4,539 cal/g. Crude protein and nonstructural carbohydrates were most concentrated during the spring growth period when stems were developing. As the stems matured during summer they became more fibrous resulting in lower protein and carbohydrate levels. Just prior to flowering, tall plants with stems approaching 1 m had significantly higher fiber, but lower ether extract, carbohydrates, and in vitro dry matter digestibility than plants with stems less than 0.5 m. Crude protein, ash, and gross energy were the same for both groups. It was concluded that spotted knapweed does have some nutritional value as a livestock forage. Spring grazing of knapweed or harvesting for a winter forage may be useful in the control of this noxious plant.