Research Notes
Consumption of Low Larkspur (Delphinium nuttallianum) by Grazing Sheep

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Abstract

Low larkspur (Delphinium nuttallianum Pritz.) poisoning causes serious economic loss to livestock producers that graze cattle on foothill and mountain ranges in western North America. In general, all Delphinium spp. are five times less toxic to sheep than to cattle. Because low larkspurs are less toxic to sheep than cattle, grazing sheep before cattle on rangelands with dense populations of low larkspur can reduce larkspur density and risk of poisoning to grazing cattle. All previous published work on sheep and larkspur interactions has involved tall larkspurs. This series of studies was conducted to determine if sheep would consume sufficient low larkspur to reduce subsequent risk to cattle. Four summer trials were conducted in Collbran, Colorado, and Soda Springs, Idaho on pastures with dense (> 9 plants · m−2) low larkspur populations. In all trials, sheep ate very little low larkspur (< 0.5% of bites). During one final trial using high sheep density (two sheep · 0.015 ha−1 for 9 d), sheep consumed little low larkspur, but animals appeared to trample much of the low larkspur. Toxic alkaloid concentrations in low larkspur ranged from 1.1 mg · g−1 to 1.6 mg · g−1 in all trials. The use of sheep to graze low larkspurs to reduce subsequent consumption by grazing cattle does not appear to be a viable option.

Resumen

La toxicosis ocasionada por el Delphinium de porte bajo (Delphinium nuttallianum Pritz.) causa serias pérdidas económicas a productores ganaderos cuyos rodeos pastorean en pastizales de piedemonte y montaña del oeste de los Estados Unidos. En general, las especies de Delphinium son cinco veces menos tóxicas para ovinos que para bovinos. Dado que Delphinium nuttallianum es menos toxica para ovinos que para bovinos, el pastoreo con ovinos previo al pastoreo de bovinos en pastizales con poblaciones densas de esta especie podría reducir el riesgo de toxicosis en bovinos en pastoreo. Todos los trabajos previamente publicados sobre las interacciones entre ovinos y Delphininum han involucrado a las especies de porte alto de este género. Esta serie de estudios se condujo para determinar si los ovinos podrían consumir suficiente cantidad de Delphinium nuttallianum como para reducir el riesgo de toxicosis subsecuente en bovinos. Se realizaron cuatro ensayos durante el verano en Collbran, Colorado, y Soda Springs, Idaho en potreros con poblaciones densas (> 9 plantas · m−2) de Delphinium nuttallianum. En todos los ensayos los ovinos consumieron cantidades muy pequeñas de Delphinium nuttallianum (< 0.5% de bocados). Durante un ensayo final, altas densidades de ovinos (dos ovejas · 0.015 ha−1 por 9 días), consumieron poco Delphinium nuttallianum, pero los animales aparentemente pisotearon la mayor parte de las plantas de esta especie. La concentración de alcaloides tóxicos en Delphinium nuttallianum osciló entre 1.1 mg · g−1 y 1.6 mg · g−1 en todos los ensayos. El uso de ovinos para consumir Delphinium nuttallianum y reducir el riesgo de toxicosis subsecuente en bovinos no aparenta ser una alternativa viable.

Section snippets

INTRODUCTION

Low larkspur (Delphinium nuttallianum Pritz.) poisoning causes serious economic loss to livestock producers grazing cattle in the western United States and Canada (Pfister et al. 1999; Pfister et al. 2003). Cattle death losses to larkspur are estimated to be 3% to 15% annually in areas where larkspurs are abundant (Nielsen et al. 1994). Low larkspurs contain a number of toxic diterpenoid alkaloids, including the primary toxic alkaloid, methyllycaconitine (MLA). The risk of poisoning is related

Animals and Management

The sheep used in these studies were one-year-old crossbred white-faced ewes raised at the US Sheep Experiment Station near Dubois, Idaho. These animals likely encountered low larkspur (D. nuttallianum) as lambs grazing on mountain rangelands near Dubois, Idaho. In all studies, sheep were introduced into experimental pastures when low larkspur was in full flower. Bite counts (% of bites) were used in all studies to document diet selection. Beginning at 0700 every day, individual animals were

Trial 1: Collbran, Colorado (2001)

Sheep ate very small amounts of low larkspur (0.4% of bites as low larkspur); other forbs and grasses comprised 64% and 35% of sheep bites, respectively. There was no effect (P > 0.8) of low larkspur density on sheep bites of low larkspur (data not shown). The toxic alkaloid concentration in low larkspur was 1.5 mg · g−1 (dry weight). Forage availability for all trials and locations is given in Table 1.

Trials 2 and 3: Soda Springs, Idaho (2004 and 2005)

There was no effect (P > 0.6) of plant phenology on low larkspur consumption by sheep (data

DISCUSSION

There are no documented losses of sheep to tall or low larkspur; thus there has been continual interest for many years by livestock producers with persistent cattle losses in using sheep to reduce risk for subsequent cattle grazing in larkspur-dominated areas. Marsh et al. (1934) reported anecdotally that sheep eat low larkspur in quantities sufficient to reduce risk to cattle, but did no research on the subject. Ralphs et al. (1991) found that sheep consumption of three different tall larkspur

IMPLICATIONS

Under free-grazing conditions, sheep ate very little low larkspur during four grazing trials. The use of sheep to graze low larkspurs to reduce subsequent consumption by grazing cattle does not appear to be a viable option. Our observations suggest that sheep can be used to trample dense low larkspur populations.

Acknowledgments

We express our thanks to Kermit Price and Ed Knoppel for their excellent assistance with the study, and to the Animal Caretakers at the Poisonous Plant Research Laboratory, Al Maciulis, Rex Probst, and Danny Hansen, for their help with animal management and transport.

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