Cattle as dispersers of hound's-tongue on rangeland in southeastern British Columbia.
Hound's-tongue (Cynoglossum officinale) is a noxious weed on forested range of western North America, which produces barbed nutlets (burrs) that attach to animals. There is anecdotal evidence that cattle are important dispersers of hound's-tongue in North America, although European studies suggest animal dispersal of hound's-tongue burrs is minimal. The role of cattle as hound's-tongue dispersers was examined on 3 range units in the Cranbrook Forest District, British Columbia. To determine the movement of burrs onto cattle, the number of burrs on marked stalks, before and after grazing, were counted. In 1993 and 1994, about 65% of the burrs stalk-1 were picked up by grazing cattle, whereas, only 14% of the burrs stalk-1 were lost in a paddock ungrazed by cattle in 1994. Individual cows were monitored for burr gains and losses during monthly moves between paddocks by photographing their faces, and counting the burrs face-1 from projected slides. Cattle also were photographed every 2 weeks while in-situ on paddocks. Within 2 to 4 weeks, cows acquired and then lost burrs as they moved within and between paddocks. These experiments suggest that cattle are major dispersers of hound's-tongue on rangelands. There was a positive, linear relationship (R2 = 0.77; p<0.001, N=13) between the mean number of burrs face-1 and the number of burr stalks ha-1 of paddock. A relationship between the percent of photographed cattle with burrs and stalk density was best described by a hyperbolic model (R2 = 0.83). With refinement, it is suggested that these relationships between burrs on cattle and hound's-tongue density on paddocks may be useful in monitoring hound's-tongue populations.