Submitted to: Rangeland Ecology and Management
Publication Type: Peer reviewed journal
Publication Acceptance Date: 7/7/2005
Publication Date: 11/1/2005
Citation: Ralphs, M.H. 2005. Conditioning sheep to graze duncecap larkspur (delphinium occidentale). Rangeland Ecology and Management. 58:628-631. Interpretive Summary: Sheep are more resistant than cattle to larkspur poisoning and thus may be used as a biological tool to graze larkspur to reduce cattle poisoning. Sheep readily graze larkspur in its mature stages, but if they are to be an effective management tool, they must graze it in the early growth stages before cattle enter the pastures. We attempted to positively condition sheep to graze tall and duncecap larkspur by dosing them with supplemental energy following consumption of larkspur. Positively conditioned sheep consumed more larkspur in preference tests in the pen and in the later part of field grazing trials than control animals. However, high alkaloid levels in larkspur in its early phenological growth stages inhibited sheep from preferentially grazing larkspur early in the grazing season, which would be necessary to prevent cattle poisoning.
Technical Abstract: Sheep are more resistant than cattle to larkspur poisoning and thus may be used as a biological tool to graze larkspur to reduce cattle poisoning. Sheep readily graze larkspur in its mature stages, but if they are to be an effective management tool, they must graze it in the early growth stages before cattle enter the allotment. In Trial 1, 18 ewes were divided into three groups of six ewes each. During conditioning, group 1 (Dextrose) was offered potted tall larkspur (Delphinium barbeyi) plants then were given dextrose IV as a positive reinforcement. This was not successful, so they were offered larkspur as a group to utilize social facilitation (SF) to increase consumption. The second group (Expose) was offered single potted plants. The third group (Control) was not exposed to tall larkspur during conditioning. In the subsequent preference test, the dextrose/SF group consumed more potted tall larkspur plants than the exposed or control groups. The dextrose/SF and control groups were then taken to tall larkspur infested mountain rangeland for a field test of the conditioning. In Trial 2, the same 18 ewes were relocated to 3 new groups for conditioning towards duncecap larkspur (D. occidentale). In the pen conditioning trial, one group was offered potted larkspur plants then were gavaged with glucose, the second were exposed to larkspur plants together as a group (SF), and the third was an untreated control. In the preference test, the glucose group ate more duncecap larkspur than the social facilitation and control group. The glucose and control groups were taken to duncecap larkspur infested mountain rangeland to test the conditioning. In both field grazing trials, the positive conditioned groups consumed more larkspur than the control groups, but it occurred later in the grazing trials when larkspur was in flower and after desirable forages had been consumed. High levels of alkaloids and other alternative palatable forages caused ewes to reject both larkspur species at the beginning of the trials. Positive conditioning to induce ewes to graze larkspur early in the grazing season was not successful,