Utilization of Larkspur by Sheep
Journal of range management
Sheep are more resistent to hukspur (Delplrinium spp.) poisoning than are cattle, and may be used as a biological tool to graze larkspur prior to cattle turn-in to reduce the risk of cattle poisoning. Sheep utilization of 3 species of larkspur was measured at 3 phenological growth stages (vegetative, bud, and flower) at 5 locations. Utilization of waxy larkspur (D. g&ucescens Wats), varied among years at Ruby, Mont. Use of duncecap larkspur (D. o&f-entuB. Wats) at Oakley, Ida., was uniformly
... ., was uniformly higher in all 3 growth stages due to closed herding practices. Use of tall larkspur D. bar&G Huth) increased as it matured. Trailing sheep through larkspur patches, or bedding them in patches greatly increased trampling of hukspur stalks and utilization of heads and leaves. Poisoning from ingestion of larkspur (Delphinium spp.) is the leading cause of cattle deaths on mountain rangeland (Aldous 1917, Nielsen and Ralphs 1988). Sheep, on the other hand, are more resistant to larkspur poisoning than cattle (Marsh et al. 1934, Olsen 1978, thus, forward grazing by sheep may be an effective strategy for reducing the availability and/ or acceptability of larkspur to grazing cattle. This in turn should reduce cattle losses from larkspur poisoning. Previous research examining the impact of forward grazing by sheep varied as a function of species of larkspur and season. For example, Marsh et al. (1934) reported sheep grazing stands of low larkspur (Delphinium nelsonii Greene) reduced incidence of cattle losses. Aldous (1917) reported that sheep grazing immature duncecap larkspur (D. occidentale S. Wats) early in the growing season eliminated subsequent poisoning of cattle. However, sheep grazed other forage in preference to tall larkspur (D. barbeyi Huth), thus increasing the threat to cattle. The underlying hypothesis of this study is that forward grazing by sheep will subsequently reduce cattle losses to larkspur poisoning by reducing availability and/ or acceptability of larkspur. This can be accomplished by sheep ingesting and/ or trampling larkspur during the early portion of the growing season. The broad objective of the studies reported herein was to examine the impact of sheep grazing on 3 species of larkspur during early growth stages. Study 1 examined the variation in consumption of waxy larkspur (D. glaucescens Wats) in the bud growth stage over a 4-year period. Study 2 was designed to quantify the amount of duncecap and tall larkspur grazed and/or trampled by sheep during the vegetative, bud, and flower growth stages among 4 locations during a single year. In addition, the relative impacts of trampling and defoliation were examined when sheep were in the grazing, trailing, or bedding modes at 2 of these locations. Alkaloid concentrations in larkspur species were measured at each site to determine if alkaloid level influenced utilization of larkspur. Study 1 Methods The study was conducted in the upper Ruby River Valley 93 km Authors are range scientist, USDA/ARS Poisonous Plant Research Laboratory, Logan, Utah; and professor range science, Utah Agr. Exp. Sta., Southern Utah State Umversw, Cedar City, Utah; and chemist, USDA/ ARS Western Regional Research Center, Albany, Calif. Manuscript accepted I5 April 1991. Utilization during the bud stage was measured at Willow Creek where larkspur occurred in the bottoms of draws in the mountain big sagebrush/ basin wildrye (Elymus cincereus Scribn. & Merr.) habitat type. Utilization during the flower stage was measured at Gravel Springs in an aspen (Populus tremuloides Michx)/ snowberry habitat type. 'Alexander, J.D. III and J.E. Taylor 1986. Sheep utilization as a control method on tall larkspur infested cattle range. Abstract 241Aldous, A.E. 1917. Eradicating tall larkspur on cattle ranges in the national forests. USDA Farmers Bull. 826. Cronin, E.H., and D.B. Nielsen. 1979. The ecology and control of rangeland larkspur. Utah Agr. Exp. Sta. Bull. 499. Manners, G.D., and M.H. Ralphs. 1989. Capillary gas chromatography of Delphinium diterpenoid alkaloids. J. Chromatography 466427-232. Marsh, C.D., A.B. Clawson, and H. Marsh. 1934. Larkspur or poison weed. USDA Farmers Bull. 98 (revised 1934). Olsen, J.D. 1978.Tall larkspur poisoning incattle and sheep. J. Amer. Vet. Med. Assoc. 173:76 pfister, J.A., M.H. Ralphs, and C.W. Manners. 1988a. Cattle grazing tall larkspur (Delphinium barbeyi) on Utah mountain rangeland. J. Range Manage. 41:118-122. Pfister, J.A., G.D. Manners, M.H. Ralphs, Z.H. Hong, and M.A. Lane. 1988b. Effects of phenology, site, and rumen fill on tall larkspur concentration by cattle. J. Range Manage. 41:509-514. Ralphs, M.H., J.D. Olsen, J.A. Pfister, and G.D. Manners. 1988. Plantanimal intractions in larkspur poisoning in cattle. J. Anim. Sci.