INFLUENCE OF ALKALOID CONCENTRATION ON ACCEPTABILITY OF TALL LARKSPUR(DELPHINIUM SPP) TO CATTLE AND SHEEP

Tall larkspur (Delphinium spp.) is a serious toxic plant problem on we stern U.S. ranges, The major toxins in tall larkspur are methyllycacon itine (MLA) and 14-deacetylnudicauline (14-DAN); the sum of both is te rmed the toxic alkaloid concentration. Toxic alkaloids comprise about 20-50% of the total alkaloid concentration in tall larkspur. Toxic and total alkaloid concentration generally declines with maturity, wherea s cattle and sheep consumption of larkspur typically increases with pl ant maturity. We hypothesized that cattle and sheep consumption of tal l larkspur was negatively related to higher concentrations of total or toxic alkaloid. We compared consumption of several collections of dri ed, ground larkspur and fresh larkspur in a series of trials. In anoth er trial, a crude alkaloid fraction was extracted with ethanol, added to alfalfa hay, and consumption compared to untreated alfalfa hay, alc ohol-treated hay, and the essentially alkaloid-free plant residue. In all cases we correlated amounts eaten with total and toxic alkaloid co ncentration. A grazing trial was also conducted to relate larkspur con sumption over time to alkaloid concentrations. Total alkaloid concentr ations in dried, whole-plant collections ranged from 9.3 to 38.8 mg/g of dry weight, whereas toxic alkaloid concentrations varied from 0.0 t o 7.1 mg/g. In one pen trial, cattle preferred a larkspur collection ( P < 0.01) that contained no toxic alkaloids but had a high total alkal oid concentration (39 mg/g). There was no correlation (P > 0.05), howe ver, between concentrations of total or toxic alkaloids and amount of dry plant consumed in this or any other trial. Conversely, sheep consu mption tended to be negatively influenced by total and toxic alkaloid concentration (P less than or equal to 0.08). In the trials with extra ct, cattle preferred the alcohol-treated hay and rejected the alkaloid -free residue (P < 0.01), whereas the alkaloid-treated hay was of inte rmediate acceptability. Cattle preferred the alkaloid-treated hay over the alkaloid-free residue, indicating that alkaloids did not deter co nsumption. Conversely, the alkaloid-treated hay was less preferred tha n either untreated or alcohol-treated hay, suggesting a negative effec t on acceptability. There was no correlation between alkaloid concentr ation and amount of treated feed eaten. In field trials, the amount of composited, fresh leaves or flowers eaten by cattle was influenced by plant part (P = 0.04), but was not related (P > 0.05) to alkaloid con centration. Cattle preferred leaves over Rowers when offered individua l plants differing in phenological stage and/or amount of shade. but a lkaloid concentration was not related to consumption. We conclude that knowledge of the concentration of total or toxic alkaloid in tall lar kspur will give little or no indication of plant acceptability to catt le. Even though accurate predictions can be made about the potential t oxicity of larkspur based on the concentration of toxic alkaloids, pre dictions about consumption must be based primarily on plant phenology.