Snakeweed: Poisonous Properties, Livestock Losses, and Management Considerations

J. Range Manage. 55: 277-284 May 2002 Snakeweed: Poisonous properties, livestock losses, and management considerations KIRK C. McDANIEL AND TIMOTHY T. ROSS Authors are Professors, Dept. of Animal and Range Sciences, New Mexico State Univ., Las Cruces, N.M. 88003. Abstract Resumen (broom, Gutierrezia sarothrae (Pursh) Britt & Snakeweeds (broom, Gutierrezia sarothrae (Pursh) Britt & "Snakeweeds" Rusby) "Threadleaf" (G. microcephala (DC.) Gray) caen den- Rusby); and threadleaf, G. microcephala (DC.) Gray) fall into y de la categoria de las malezas toxicas que raramente causan that class of poisonous weeds that seldom cause direct livestock tro perdidas directas de ganado porque ellas no le gustan al ganado losses because they are highly unpalatable and animals rarely consumen grandes cantidades de mate- consume large quantities of plant material. However, when y raramente los animales de estas plantas. Sin embargo, cuando el snakeweed becomes dominant on rangeland and retards growth rial vegetal llega a ser dominante en el pastizal retarda el of desirable forage, then indirectly it becomes a serious hazard to "Snakeweed" y de especies deseables, entonces se convierte en un animal health. Confined and rangeland feeding trials conducted crecimiento serio peligro para la salud animal. Estudios de alimentacion en at New Mexico State University with cattle and sheep have failed en pastizal realizados en la Universidad Estatal to elicit reproductive failure with elevated snakeweed dosages. confinamiento y Mexico con ovinos bovinos han fallado en lograr un was shown to impair certain reproductive functions de Nuevo y Snakeweed con dosis elevadas de "Snakeweed". such as pituitary responsiveness to luteinizing hormone, and fracaso reproductivo "Snakeweed" mostro deteriorar ciertas funciones reproductivas caused mild hepato-renal toxicity. Under rangeland conditions, la respuesta de la pituitaria a la hormona luteinizante livestock grazing in areas dominated by snakeweed reportedly tales como causo una toxicidad hepato-renal ligera. Bajo condiciones de have more serious problems, such as abortion. A commonality y el ganado apacentando en areas dominadas por between confined feeding trials and rangeland grazing trials is pastizal, tiene problemas mucho mas serios como abortos. that in the presence of snakeweed, animals typically display "Snakeweed" Algo comun entre los ensayos en confinamiento los de apacen- symptoms associated with a low-plane of nutrition such as lack of y snakeweed tamiento en pastizales es que en la presencia de "Snakeweed" los gain, emaciation, and occasional death. To reduce piano interven- animales tipicamente muestran sintomas asociados con un dominance and improve range condition, management de peso, or fire control may be necessary. nutricional bajo, tai como la falta de ganancia tions such as herbicide Para reducir la dominancia del the decision regarding snakeweed control is the demacracion y muerte ocasional. Complicating mejorar la condicion del pastizal, es necesario uncertainty about treatment life and whether this relatively "Snakeweed" y practicas de manejo tai como el use de herbicidas o short-lived perennial weed might be eliminated by natural caus- realizar fuego para controlar esta planta. Algo que complica la decision es. Knowing the snakeweed population pattern in a given area respecto al control del "Snakeweed" es la incertidumbre acerca greatly enhances management decisions. de la duracion del tratamiento y si esta especie perenne de vida relativamente corta pudiera ser eliminada por causas naturales. Conociendo el patron de la poblacion de "Snakeweed" de una Key Words: Poisonous plant, range weed, livestock grazing, area dada mejora grandemente las decisiones de manejo. broom snakeweed (Gutierrezia sarothrae (Pursh) Britt & Rusby), threadleaf snakeweed (Gutierrezia microcephala (DC.) Gray) mainly in the Chihuanhuan and Sonoran deserts of Mexico and Rusby) and Broom (Gutierrezia sarothrae (Pursh) Britt & the southwestern United States. threadleaf (G. microcephala (DC.) Gray) snakeweed are short- Snakeweeds contain a rich mixture of alkaloids, flavonoids, lived perennial shrubs within the Asteraceae family. Because they saponins, terpenes, and other compounds that are often causal ecological are similar in appearance and often occupy the same agents in various plants that poison rangeland livestock. These niches, they are commonly referred together in the literature as substances also render snakeweed highly unpalatable so that indige- simply, snakeweed (Sterling et al. 1999). Both species are when given a choice animals usually will not eat the foliage. Bite distributed from nous to North America with broom snakeweed into a snakeweed leaf and you'll quickly appreciate from the is found Mexico to southern Canada, while threadleaf snakeweed harsh burning taste why other common names, such as fireweed and turpentine weed are so appropriate. Snakeweeds are rarely NM This paper was supported by the New Mexico Agr. Exp. Sta., Las Cruces, eaten by any large wild or domestic animal (Smith et al. 1991) 88003 and was funded in part by a special grant for Broom Snakeweed Research. Author to whom correspondence should be addressed. Dept. of Animal and and with the exception of a few specialist foliage feeding insects, Range Sciences, New Mexico State University, Las Cruces, NM 88003. Phone: such as the red-kneed grasshopper (Hesperotettix viridis (505) 646-1191; Fax: (505) 646-5441; E-mail: [email protected]. [Thomas]) (Thompson et al. 1995, Foster et al. 1981, Richman Manuscript accepted 2 Sept. 01. 277 JOURNAL OF RANGE MANAGEMENT 55(3) May and Thompson 1995) snakeweeds are Livestock displaying symptoms from duce isocaloric and isonitrogenous diets. rarely damaged by grazing. snakeweed poisoning under rangeland con- Smith et al. (1991) examined the response Pieper (1989) reviewed literature report- ditions are likely to have a decreased nutri- of rats to increasing levels of snakeweed ing snakeweed in herbivore diets and ent status and body condition accelerated in the diet ranging from 0 to 25%. These found it usually absent but occasionally as by malnutrition. Healthy grazing animals authors found that pregnancy rates much as 3 to10% of grazed diets in cattle, are not likely to eat the plant unless other decreased when dietary snakeweed horses, sheep, goats, mule deer, jack rab- forage is extremely scarce (Mathews exceeded 12.5 %. They also reported that bits, and pronghorn antelope. When snake- 1936). Thus intuitively, rangelands with reproductive functions were impaired weed is grazed by livestock it is most like- poor forage conditions (or range condition) before evidence of liver or kidney damage. ly because it is the predominant green are areas of concern but can be remedied in In the Smith et al. (1991) study, they plant among other dormant or scarce the short term with nutrient supplementa- found that after 35 days of snakeweed species. Cattle, sheep, and horses are tion (Strickland et al. 1998) and in the long feeding that rats exhibited evidence of reportedly killed by ingesting 10 to 20% term by increasing forage availability. liver and biliary toxicosis indicated by ele- of an animals body weight with snake- vated alkaline phosphates, gamma-glu- weed (Kingsbury 1964), but problems Toxicity Studies at New Mexico tamyltranspeptidase, and alanine amino- with reproduction and abortion are more State University (NMSU) from 1980 transferase. When pregnant rats were fed commonly reported (Dollahite and to 2000 snakeweed at levels above 10% in the diet, Anthony 1957, Smith and Flores- Several studies have confirmed snake- embryonic mortality and early fetal death Rodriguez 1989). weed toxicity under confined feeding con- was noted. Also, blood urea nitrogen and While snakeweed poisoning problems ditions but, to our knowledge, no research creatinine concentrations were elevated can not be discounted, the literature sug- has been able to demonstrate snakeweed suggesting some damage to the kidneys. In is gests that it the plants competitive poisoning under actual rangeland grazing the aforementioned experiments by Smith nature that causes major economic damage experiments. Beck et al. (1999) grazed et al. (1991), snakeweed was harvested by to livestock (5 producers. Under dense mature cows in various experiments on hand clipping the new growth portion to snakeweed stands losses diminished from rangelands dominated by snakeweed on 10 cm) of the plant during pre-bloom. forage and livestock production usually far the Chihuahuan Desert Rangeland Oetting et al. (1990) fed snakeweed to outweighs it's toxic properties. In this Research Center near Las Cruces, N.M. ewes at levels ranging from 0 to 25% of paper we discuss some recent findings from 1992 to 1998 and never witnessed diets. With alfalfa hay as the base feed from research pertaining to snakeweed animals eating the plant. Similarly, graz- mixed with 25% snakeweed, ewes easily toxicology and management. We have ing trials with goats in the same area from consumed the diet. Ewes fed 12.5 and placed special emphasis on research we 1989 to 1993 reported little use of snake- 25% snakeweed with alfalfa hay experi- have been involved in at New Mexico weed except when other herbage was enced longer estrous cycles and higher State University'. grazed out (Beck et al. 1996). According serum progesterone concentrations than to Beck et al. (1996), heavy goat stocking ewes fed less snakeweed. When the base Toxicity Problems for 5 summer seasons resulted in no

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