PS2-16. Larkspur Alkaloid Sorption by Clays to Mitigate Livestock Poisoning.

Abstract The management of beef cattle on rangelands with toxic larkspur (Delphinium spp.) is problematic. Beef producers with toxic larkspur on their ranges can have yearly herd death losses of up to 10%. Work at this laboratory has shown that cattle supplemented with a clay-mineral salt mixture were less susceptible to larkspur than non-supplemented animals (Stonecipher et al., 2022, DOI: 10.1093/jas/skac133). This suggested that a component of the clay-mineral salt mixture provided cattle greater resistance to larkspur. The objective of this work was to identify and measure the ability of clays to sorb and sequester the larkspur alkaloid methyllycaconitine (MLA). Clays were first tested in an in vitro rumen culture system and then in vivo in cattle. Methods: Animal work was approved by the Utah State University IACUC (protocol # 12987). Nine Holstein heifers were used for the in vivo studies and rumen fluid was obtained from two fistulated Angus cows for the in vitro studies with McDougall’s buffer, plant material, and the clays. Data are represented as mean ± standard error, statistical significance was set at P < 0.05. Results and Discussion: We tested bentonite, kaolin, and zeolite in vitro for their sorption of MLA. One g of dried ground larkspur was incubated with 1 g each of the three clays in 500 mL of McDougall’s buffer for 24 h (n = 4 rumen cultures each). Bentonite was most effective at sorbing MLA with a concentration of 0.03 ± 0.02 µg/mL MLA verses 7.75 ± 0.47 µg/mL for control and 9.8 ± 2.3 and 11.9 ± 1.7 µg/mL for kaolin and zeolite respectively (P < 0.0001 ANOVA, Dunnett’s multiple comparisons test). The MLA concentrations in solution were correlated to clay cation sorption capacity (Pearson correlation coefficients, r2 = -0.99, 0.99). Based upon the results from the rumen cultures, we tested bentonite in cattle. Nine cattle were orally dosed with dried ground larkspur plant material at 4 mg/kg MSAL-type alkaloids and either control, 31, 125, or 250 mg of bentonite clay per g of plant material. Eight h after oral dosing, blood was obtained and serum MLA concentrations determined. The serum MLA concentrations were 287 ± 22, 298 ± 25, 117 ± 23, and 67 ± 78 ng/mL for control, 31, 125, or 250 mg bentonite per g of plant material, respectively. The serum MLA concentrations of the 125 and 250 mg of bentonite per g of plant material were significantly different from the control (P < 0.05, one-way ANOVA, Dunnett’s multiple comparisons test). These results suggest that bentonite can sorb MLA from the rumens of cattle in a dose-dependent manner, and that bentonite has the potential to provide cattle greater resistance to the toxic actions of larkspur.