Toxic Principle

Diterpene alkaloids, methyllycaconitine, 14-deacetylnudicauline, and nudicauline. The alkaloids act principally at the neuromuscular junction causing a curare-like blockade with resulting muscle weakness and paralysis.

Description

Tall larkspurs are erect, perennial, herbaceous plants with simple or branched hollow stems; the leaves are alternate and palmately divided. The flowers are perfect and irregular, and are carried in terminal racemes. The flowers are dark blue in color. There are 5 sepals, the upper most one having an obvious spur. The corolla comprises two sets of two petals each, the two lower ones forming a claw and the upper two extending into the spur. The flowers have multiple stamens and 3 pistils which may be fused at the base. The fruits are follicles that split open to release numerous dark brown/black seeds.

Gastrointestinal

Bloat, secondary to the muscle paralysis induced by the alkaloids, is a major contributor to the rapid death of cattle.

Musculoskeletal

Muscle tremors, weakness, staggering gait and recumbency.

Treatment

Avoid stressing the affected animals. Gently herd the cattle away from the larkspur area. Where possible give physostigmine intravenously (0.08mg/kg) with as little stress as possible. Neostigmine sulfate administered intravenously or intramuscularly at a dose of 0.02 - 0.04 mg/kg can also be used for treating larkspur poisoned cattle. Keep the animal on its sternum to reduce bloating, and if necessary treat the bloat by passing a stomach tube, or by trocarizing the rumen.

Respiratory System

Death due to respiratory paralysis and bloat.

Nervous System

Muscular paralysis due to the neurotoxic alkaloids binding to acetylcholine receptor sites causing muscular paralysis.

Diagnosis

Sudden deaths of cattle on summer range at higher altitudes where larkspur is abundant should prompt suspicion of larkspur poisoning. Rumen contents and the suspect larkspur plants can be submitted to the Poisonous Plants Research Lab in Logan, Utah for analysis. When alkaloid concentrations are <3 mg/gm of plant, cattle can safely eat larger amounts.

Special Notes

Management Strategy for tall larkspur. As tall larkspur is most palatable when the plant is developing and elongating its flowers stalks, it is important to keep cattle off of range areas where the tall larkspur is in this stage of growth. Large flocks of sheep can be useful management tools as they will eat and trample the larkspur making it less available to cattle afterwards. Herbicides can be effective and economical in eliminating stands of tall larkspur, thereby reducing "hot spots" where cattle are likely to rapidly ingest large quantities of the plants. Mineral Supplementation - Deleterious effects of larkspur consumption may be reduced by mineral supplementation. Angus steers dosed with a standardized amount of MSAL-type alkaloids in ground larkspur exhibited less larkspur-induced muscle weakness following 33 days of mineral supplementation. This suggests that mineral supplementation may reduce the deleterious effects of larkspur consumption. in a separate test, mineral supplementation did not reduce larkspur consumption (4). Herbicide Control of Larkspur Picloram (Tordon) at 2.2 lb/acre is effective in controlling tall larkspur when applied in the vegetative, bud, and flower stages. 2,4-D and picloram have been shown to be effective at controlling low and plains larkspur. References 1. Green BT, Gardner DR, Pfister JA, Cook D. Larkspur Poison Weed: 100 Years of Delphinium Research. Rangelands, 31:22-27. 2009. 2. Green BT et al: Effects of larkspur (Delphinium barbeyi) on heart rate and electrically evoked electromyographic response of the external anal sphincter in cattle. Am J of Vet Research 2009, 70: 539-546. 3. Panter KE et al: Larkspur poisoning: toxicology and alkaloid structure-activity relationships. Biochemical Systematics and Ecology 2002, 30:2113-128 4. Stonecipher CA, Green BT, Welch KD, Gardner DR, Fritz SA, Cook D, Pfister JA. Mineral-salt supplementation to ameliorate larkspur poisoning in cattle. J Anim Sci. 2022 May 1;100(5):skac133. doi: 10.1093/jas/skac133. PMID: 35419604; PMCID: PMC9115907.