James A. Pfister

Tall Larkspur Ingestion: Can Cattle Regulate Intake Below Toxic Levels

Tall larkspur (Delphinium barbeyi) is a toxic forb often consumed by cattle on mountain rangelands, with annual fatalities averaging about 5%. This study examined the relationship between food ingestion and toxicity in cattle. Two grazing studies suggested that larkspur consumption above 25–30% of cattle diets for one or two days led to reduced larkspur consumption on subsequent days. We subsequently hypothesized that cattle can generally limit intake of larkspur to sublethal levels. This hypothesis was tested by feeding a 27% larkspur pellet in experiment 1. Cattle given a 27% larkspur pellet ad libitum showed distinct cyclic patterns of intake, where increased larkspur consumption on one or two days was followed by reduced (P < 0.025) consumption on the following day. The amount of larkspur (mean 2007 g/day; 17.8 mg toxic alkaloid/kg body wt) consumed was just below a level that would produce overt signs of toxicity. Experiment 2 was conducted to examine cattle response to a toxin dose that varied with food intake. Lithium chloride (LiCl) paired with corn ingestion was used as a model toxin, and we hypothesized that if increased (decreased) consumption was followed by a stronger (weaker) dose of LiCl, cattle would show a transient reduction (increase) in corn intake. There was no difference (P > 0.05) between controls and treatment animals at the 20 or 40 mg LiCl/kg dose in the percentage of corn consumed, but the 80 mg LiCl/kg dose induced a cyclic response (mean 46%) compared to intake by controls (mean 96%) (P < 0.001). At the 80 mg/kg dose, LiCl induced an aversion to corn; when corn intake decreased on subsequent days and LiCl dose also decreased, cattle responded by increasing corn intake and apparently extinguishing the transient food aversion. Experiment 3 was similar to the LiCl trial, except that tall larkspur was the toxin. Cattle responded to oral gavage of ground larkspur with distinct cycles; days of higher corn consumption were followed by one to three days of reduced consumption. Corn intake for controls was higher (P < 0.01) than for larkspur-treated animals (means 84 and 52%, respectively; day × treatment interaction P < 0.01). The threshold for toxic effects on corn intake was 14 mg toxic alkaloid/kg body weight. In conclusion, cattle apparently limit ingestion of some toxins so that periods of high consumption are followed by periods of reduced consumption to allow for detoxification. Cyclic consumption generally enables cattle to regulate tall larkspur consumption below a toxic threshold and allows cattle the opportunity to safely use an otherwise nutritious, but toxic, plant.

Dietary selection by goats and sheep in a deciduous woodland of northeastern Brazil.

The dietary botanical composition of indigenous sheep and goats was determined in the semiarid tropics of northeastern Brazil, using esophageally fistulated animals. Sheep and goats selected similar diets during the dry season (May-Dec.). Main dietary components for both species were dried forbs and browse. Leaf litter from the deciduous trees provided the majority of dry season forage (NO-1,500 kg/ha) and was a crucial element of dry season diets (20-70%). During the wet season (Jan.-Apr.), sheep selected mainly grasses and forbs, while goats rapidly shifted among grasses, forbs, and browse. By displaying attributes of both browsers and grazers, neither sheep nor goats conformed to traditionally rigid characterization. We found no indication that goats are better adapted for survival in this tropical environment than are sheep because of the botanical composition of their diets. Management implications of this study for the cutrtinga vegetation zone are discussed. Although range science literature is replete with studies reporting detailed data on diets of cattle and sheep, few investigations have examined diets of goats grazing alone, or in common with other livestock (Malechek and Provenza 1983). Van Dyne et al. (1980) catalogued studies of livestock diets, and noted 5 and 38 such studies for goats and sheep, respectively. Only 3 studies listed in this paper compared dietary selections by goats and sheep grazing together on common ranges. No work has been done using esophageally fistulated animals to examine diets of either goats (Capra hircus) or sheep (&is aries) in northeastern Brazil. Generally comparisons of the dietary selections of goats have been made with sheep of European origin. Little information is currently available on selectivity of tropical hair sheep or goats. At the time of this research, authors were graduate research assistant and professor, respectively, Department of Range Science? Utah State University, Logan Utah, 84322. J. PI&r is presently research scientist, Department of Range and Wildlife Management, Texas Tech University, Lubbock 79409. Research was financed by USAID Grant No. AID/DSAN/XII-G-0049 as part of the Small Ruminant Collaborative Research Support Program in cooperation with Empress Brasileira de Pesquisa Agropecuaria. The authors wish to thank the personnel of the Centro National de Pesquisa de Caprinos for provision of physical facilities and assistance during the study. We are especially grateful to Venceslau Alves Costa, Animal Husbandryman, for his assistance. Manuscript preparation supported by Texas Tech University. Manuscript accepted 25 April 1985. 24 Goats have acquired a reputation for survivability on harsh, degraded rangeland (Devendra 1978). This may be due, in part, to unique dietary selections made by goats (McCammon-Feldman et al. 1981). French (1970) maintained that high survivability by goats was related to their relatively unspecialized feeding habits. Increased specialization implies fewer plant species or parts eaten. Observations have indicated that goats eat a wider array of plant species than do other livestock (French 1970, Wilson et al. 1975). Conversely, Van Soest (1980, 1982) stated that goats should display more specialized feeding habits than do sheep, based on body size, gastrointestinal capacity, nutrient requirements, and feeding strategy. He classified goats and sheep in 2 ways. First, goats are classified as forbor browsepreferring intermediate (between browsers and grazers) feeders, and sheep as grasspreferring intermediate feeders. Van Soest’s (1982:7) second classification lists goats as intermedite browsers, and sheep as grazers. Livestock producers in northeastern Brazil prefer to raise sheep over goats (Gutierrez et al. 1981) because of many complex socioeconomic factors (Primov 1982). For instance, sheep do not require the less penetrable, more expensive fencing required for goats, especially adjacent to cropland. On the other hand, goats are often viewed by Brazilian producers as a form of drought insurance because of their reputed survivability and minimal requirements for supplemental feeds during droughts. The objectives of this study were to determine the botanical composition of goat and sheep diets on a seasonal basis, and to evaluate the selective feeding strategies of goats and sheep. Such information would provide a basis for more sophisticated management and insight into the question of comparative adaptability of the 2 species.

Behavioral toxicology of livestock ingesting plant toxins.

Improved usage of rangelnnds for livestock production requires better ways to reduce losses caused by poisonous plants, such as management practices to minimize ingestion and treatments to improve animal tolerance of ingested poisonous plants. In ruminants, gastrointestinri microbes can detoxify piant compounds, and this capacity has been enhanced in a few cases by deliberate modification of rumen microbial populations. Some plants are poisonous because ingested plant material is made toxic by microbial fermentation in the rumen, and better understanding of such toxifications will provide opportunities to diminish poisonings of that type. Absorption of toxic substances from the gastrointestinal tract into blood and lymph may be modifled by feeding binding agents such as clay, resins, and indigestible fibers, or by pharmaceuticals that interfere with absorption of toxicants. Agents that induce or inhibit biotransformational enzymes in tissues of the host animal might modify animal tolerance of some plant toxicants. Provision of substances that serve as co-substrates of detoxification can enhance animal tolerance of other types of plant toxicants. Some reports that illustrate these approaches have been reviewed, and questions have been raised to stimulate further research.

Conditioned taste aversion: potential for reducing cattle loss to larkspur.

Barbey larkspur (Delphinium barbeyi L. Huth) is a palatable poisonous plant that causes a large number of cattle deaths on mountain rangelands. The objective of the study was to determine whether or not cattle could be conditioned to avoid eating larkspur. Five heifers were conditioned to avoid eating larkspur by intraruminal infusion of lithium chloride whenever they consumed larkspur in a pen feeding trial. Five control heifers were likewise infused with distilled water. Following the conditioning, the heifers were taken to mountain rangeland in central Utah and observed in 1986 and 1987. The non-averted heifers consumed larkspur throughout the 1986 field trial, while the averted heifers generally consumed little larkspur. The aversion from the previous summer persisted as the averted heifers refused to eat larkspur in the first grazing trial in 1987. During the second grazing trial in 1987, the averted heifers were placed in a pasture with non-averted heifers to determine if social influences would affect learned aversions. A rapid breakdown of the aversions was observed and the averted heifers continued consuming larkspur after being separated from non-averted heifers.

Dose response of sheep poisoned with locoweed (Oxytropis sericea)

Locoweed poisoning occurs when livestock consume swainsonine-containing Astragalus and Oxytropis species over several weeks. Although the clinical and histologic changes of poisoning have been described, the dose or duration of swainsonine ingestion that results in significant or irreversible damage is not known. The purpose of this research was to document the swainsonine doses that produce clinical intoxication and histologic lesions. Twenty-one mixed-breed wethers were dosed by gavage with ground Oxytropis sericea to obtain swainsonine doses of 0.0, 0.05, 0.1, 0.2, 0.4, 0.8, and 1.0 mg/kg/day for 30 days. Sheep receiving ≥0.2 mg/kg gained less weight than controls. After 16 days, animals receiving ≥0.4 mg/kg were depressed, reluctant to move, and did not eat their feed rations. All treatment groups had serum biochemical changes, including depressed α-mannosidase, increased aspartate aminotransferase and alkaline phosphatase, as well as sporadic changes in lactate dehydrogenase, sodium, chloride, magnesium, albumin, and osmolarity. Typical locoweed-induced cellular vacuolation was seen in the following tissues and swainsonine doses: exocrine pancreas at ≥0.05 mg/kg; proximal convoluted renal and thyroid follicular epithelium at ≥0.1 mg/kg; Purkinjes cells, Kupffers cells, splenic and lymph node macrophages, and transitional epithelium of the urinary bladder at ≥0.2 mg/kg; neurons of the basal ganglia, mesencephalon, and metencephalon at ≥0.4 mg/kg; and cerebellar neurons and glia at ≥0.8 mg/kg. Histologic lesions were generally found when tissue swainsonine concentrations were ≅150 ng/g. Both the clinical and histologic lesions, especially cerebellar lesions are suggestive of neurologic dysfunction even at low daily swainsonine doses of 0.2 mg/kg, suggesting that prolonged locoweed exposure, even at low doses, results in significant production losses as well as histologic and functional damage.

Swainsonine and endophyte relationships in Astragalus mollissimus and Astragalus lentiginosus.

Locoweeds are defined as Astragalus and Oxytropis species that induce locoism due to the toxic alkaloid swainsonine. Swainsonine was detected in all parts of Astragalus lentiginosus and Astragalus mollissimus , with greater concentrations found in the aboveground parts. Undifilum oxytropis , a fungal endophyte responsible for the synthesis of swainsonine, was detected in all plant parts of A. lentiginosus and A. mollissimus. The amount of endophyte within a plant part does not always correspond to the concentration of swainsonine in the same part. Plants of A. mollissimus and A. lentiginosus can be divided into two chemotypes: those that contain swainsonine (>0.1%; chemotype 1) and those that contain little or no detectable swainsonine (<0.01%; chemotype 2). Chemotype 1 plants in both species had quantitatively higher amounts of endophyte compared to chemotype 2 plants. Swainsonine and endophyte amounts were not uniformly distributed within stalks of the same plant. For that reason, repeated sampling of stalks from the same plant during one growing season may provide misleading results. Sequence variants of U. oxytropis exist within populations of A. mollissimus, A. lentiginosus, and Oxytropis sericea and do not correlate with chemotype. These findings suggest several possible reasons for differential concentrations of swainsonine that will be tested in future work.

Production of the alkaloid swainsonine by a fungal endosymbiont of the Ascomycete order Chaetothyriales in the host Ipomoea carnea.

Some plant species within the Convolvulaceae (morning glory family) from South America, Africa, and Australia cause a neurologic disease in grazing livestock caused by swainsonine. These convolvulaceous species including Ipomoea carnea contain the indolizidine alkaloid swainsonine, an inhibitor of α-mannosidase and mannosidase II, and polyhydroxy nortropane alkaloids, the calystegines which are glycosidase inhibitors. Swainsonine has been shown to be produced by a fungal endosymbiont in legumes of the Astragalus and Oxytropis genera, where it causes a similar neurologic disease in grazing livestock called locoism. Here we demonstrate that I. carnea plants are infected with a fungal endosymbiont that was cultured from its seeds and which produced swainsonine in pure culture but not the calystegines. The same fungal endosymbiont was detected by PCR and by culturing in I. carnea plants containing swainsonine. The fungal endosymbiont belongs to the Ascomycete order Chaetothyriales. Plants derived from fungicide-treated seeds lacked swainsonine, but calystegine concentrations were unaltered.

Toxic alkaloid concentration in tall larkspur species in the western U.S.

Larkspur (Delphinium spp.) kills more cattle on mountain rangelands in the western U.S. than any other plant, disease or predator. The concentration of toxic alkaloids was measured in 4 larkspur species, at 10 locations, at 2-week intervals during the growing season. In addition, multi-year samples from previous studies were analyzed to determine year-to-year variation in toxic alkaloids. Mountain larkspur (D. glaucum Wats.) had the highest concentration of toxic alkaloids averaged over growth stages (1.01% of dry weight), tall, (D. barbeyi (L.) Huth) and waxy larkspur (D. glaucesens Rydb) were intermediate (0.65 and 0.49% respectively), and duncecap (D. occidentale S. Watts) was lowest (0.29%). Toxic alkaloid concentration generally declined as the plants matured. However, toxic alkaloids in tall larkspur at Yampa, Colo. increased slightly in the pod stage, and toxic alkaloids in waxy larkspur increased from the vegetative to the bud stage. Concentration of toxic alkaloids in tall and duncecap larkspur leaves were higher in plants growing in open sunlight than those shaded under aspen or conifer canopy. Toxic alkaloid concentration varied among individual plants (C.V. 20-60%). Knowledge of the toxic alkaloid concentration of larkspur populations can be used to predict the risk of larkspur poisoning.

Effects of phenology, site, and rumen fill on tall larkspur consumption by cattle.

AbStlBCt Tall I8rkspur (De~hinh burbeyj) is a m8jor cause of livestock death on mount8in ranges. The influence of plant phenoiogy, grazing site, 8nd rumen fill on tall lukapur consumption ~8s evaluated during July 8nd August, 19%7. Livestock consumption of l8rkspur ~8s determined using bite counts during 4 phenologierrl st8ges: bud, e8riy flower, flower, and pod. Further, we ex8mined i8rkspur ingestion in a shaded tree site 8nd in UI open sun site 8t 0, 50, urd 100% rumen fill levels using rumiarlly c8nnuUed steers. Steers on the 0, 50,8nd 100% fill levels consumed 9,15, and 17% Irrkspur, respectively (fiO.15). ,There ~8s 8 site effect (-0.06) with steers eating 17 8nd 11% lukspur in the shade and sun sites, respectively. Over the summer, iukspur comprised 6% of cattle diets. No llukspur ~8s consumed during the bud st8ge. Larkspur consumption pe8ked at 10% of c8ttie diets during the pod strge. Lepves of t8ii larkspur contrined >3% total 8lk8loids (dry weight) in erriy July, but declined greatly with matwtion. Lukspur ~8s very nutritious, with crude protein levels 12 to 20%, and fiber levels <20% during most of the summer. C8ttie diets, as determined with esopbnge8lly flstul8ted animals, were also high in crude prottin 8nd low ia fiber during the summer. We propose a toxic window hypdbesisn~g~~~~~mdtoxidty.Thishypo~~ predicts th8t most c8ttie losses will occur during the flowering st8ge. We found tbrt t8ll iukspur ~8s unp8l8t8bie to c8ttie from the bud st8ge until the flowering r8cemes hrd eiong8ted, md then consumption generally incre8sed with pl8nt nmtmntion. Even though p8l8tPbility md consumption lncrersc during the gr8zing season, c8ttle c8n graze tall I8rkspur with a much lower risk of toxicosis when toxicity is low lrter in the gruing se8eon.

Stereoselective Potencies and Relative Toxicities of Coniine Enantiomers

Coniine, one of the major toxic alkaloids present in poison hemlock ( Conium maculatum), occurs in two optically active forms. A comparison of the relative potencies of (+)- and (-)-coniine enantiomers has not been previously reported. In this study, we separated the enantiomers of coniine and determined the biological activity of each enantiomer in vitro and in vivo. The relative potencies of these enantiomers on TE-671 cells expressing human fetal nicotinic neuromuscular receptors had the rank order of (-)-coniine > (+/-)-coniine > (+)-coniine. A mouse bioassay was used to determine the relative lethalities of (-)-, (+/-)-, and (+)-coniine in vivo. The LD 50 values of the coniine enantiomers were 7.0, 7.7, and 12.1 mg/kg for the (-)-, (+/-)-, and (+)- forms of coniine, respectively. The results from this study demonstrate that there is a stereoselective difference in the in vitro potencies of the enantiomers of coniine that directly correlates with the relative toxicities of the enantiomers in vivo.