Water extraction on Mars for an expanding human colony.

In-situ water extraction is necessary for an extended human presence on Mars. This study looks at the water requirements of an expanding human colony on Mars and the general systems needed to supply that water from the martian atmosphere and regolith. The proposed combination of systems in order to supply the necessary water includes a system similar to Honeybee Robotics' Mobile In-Situ Water Extractor (MISWE) that uses convection, a system similar to MISWE but that directs microwave energy down a borehole, a greenhouse or hothouse type system, and a system similar to the Mars Atmospheric Resource Recovery System (MARRS). It is demonstrated that a large water extraction system that can take advantage of large deposits of water ice at site specific locations is necessary to keep up with the demands of a growing colony.

Relationship between the endophyte Embellisia spp. and the toxic alkaloid swainsonine in major locoweed species (Astragalus and Oxytropis).

Locoweeds (Astragalus and Oxytropis spp. that contain the toxic alkaloid swainsonine) cause widespread poisoning of livestock on western rangelands. There are 354 species of Astragalus and 22 species of Oxytropis in the US and Canada. Recently, a fungal endophyte, Embellisia spp., was isolated from Astragalus and Oxytropis spp. and shown to produce swainsonine. We conducted a survey of the major locoweeds from areas where locoweed poisoning has occurred to verify the presence of the endophyte and to relate endophyte infection with swainsonine concentrations. Species found to contain the fungal endophyte and produce substantial amounts of swainsonine were A. wootoni, A. pubentissimus, A. mollissimus, A. lentiginosus, and O. sericea. Astragalus species generally had higher concentrations of swainsonine than Oxytropis. Swainsonine was not detected in A. alpinus, A. cibarius, A. coltonii, A. filipes, or O. campestris. The endophyte could not be cultured from A. mollissimus var. thompsonii or A. amphioxys, but was detected by polymerase chain reaction, and only 30% of these samples contained trace levels of swainsonine. Further research is necessary to determine if the endophyte is able to colonize these and other species of Astragalus and Oxytropis and determine environmental influences on its growth and synthesis of swainsonine.

Locoweed (Oxytropis sericea)-induced lesions in mule deer (Odocoileius hemionus).

Locoweed poisoning has been reported in wildlife, but it is unknown whether mule deer (Odocoileius hemionus) are susceptible. In areas that are heavily infested with locoweed, deer and elk (Cervus elaphus nelsoni) have developed a spongiform encephalopathy, chronic wasting disease (CWD). Although these are distinct diseases, no good comparisons are available. The purpose of this study was to induce and describe chronic locoweed poisoning in deer and compare it with the lesions of CWD. Two groups of four mule deer were fed either a complete pelleted ration or a similar ration containing 15% locoweed (Oxytropis sericea). Poisoned deer lost weight and developed a scruffy, dull coat. They developed reluctance to move, and movement produced subtle intention tremors. Poisoned deer had extensive vacuolation of visceral tissues, which was most severe in the exocrine pancreas. Thyroid follicular epithelium, renal tubular epithelium, and macrophages in many tissues were mildly vacuolated. The exposed deer also had mild neuronal swelling and cytoplasmic vacuolation that was most obvious in Purkinje cells. Axonal swelling and dystrophy was found in many white tracts, but it was most severe in the cerebellar peduncles and the gracilis and cuneate fasciculi. These findings indicate that deer are susceptible to locoweed poisoning, but the lesions differ in severity and distribution from those of other species. The histologic changes of locoweed poisoning are distinct from those of CWD in deer; however, the clinical presentation of locoweed poisoning in deer is similar. Histologic and immunohistochemical studies are required for a definitive diagnosis.

Conditioning cattle to graze broom snakeweed (Gutierrezia sarothrae).

Broom snakeweed (Gutierrezia sarothrae) is the most widespread range weed in North America. We attempted to positively condition cattle to graze broom snakeweed to create a biological tool to decrease the competitive ability of snakeweed in a plant community. Fifteen yearling heifers were divided into three treatment groups receiving different supplements: 1) cornstarch, 2) starch with ground snakeweed, and 3) a control (no supplements). Heifers were fed fresh snakeweed, and then were gavaged with the respective supplements to provide positive feedback to enhance their acceptance of snakeweed. The starch group consumed more snakeweed in the pen conditioning trial (P = 0.02). The starch and control groups were then taken to the field for two grazing trials. In the spring grazing trial, there was no snakeweed consumed in the free-ranging part of the trial; however, when the pasture size was decreased, the heifers started to consume snakeweed as alternative forages became less abundant. In the second small pasture trial, heifers in the positively conditioned group consumed more snake-weed than those in the control group (16 vs. 5% of bites, P < 0.001). In the fall grazing trial, little snakeweed was consumed in the free-ranging part of the trial. When the pasture size was decreased, both positively conditioned and control groups increased snakeweed consumption up to 35% of bites. In the small pastures of both the spring and fall grazing trials, 36 to 59% of snakeweed plants were grazed. Cattle can be forced to graze snake-weed in a short-duration, high-intensity grazing strategy.

Distribution of norditerpene alkaloids in tall larkspur plant parts through the growing season.

Previous research showed that toxic and total alkaloid pools in tall larkspur (Delphinium barbeyi) increased during early growth, then declined precipitously during the late flower and pod stage of growth. The objective of this study was to measure the concentration and pools of toxic and total alkaloids in tall larkspur plant parts, including roots, and to evaluate the changes in these pools over the growing season as an estimate of diterpenoid alkaloid kinetics in tall larkspur. Twenty entire plants were harvested at each phenological stage: beginning of growth in the spring, early flower, early pod, late pod, and senescence. The plants were separated into their respective parts, freeze-dried, extracted, and analyzed for toxic and total alkaloid concentration, and alkaloid pools were calculated. Concentration of toxic and total alkaloids in leaves and stems declined as the plants matured, while concentration in flowers and pods increased (P < 0.004). Concentration of alkaloids in the root declined in the early growth, then increased at the end of the season (P = 0.002). Alkaloid pools in the root decreased during early growth, with a corresponding increase of pools in foliar parts. In the late flower and pod stage, alkaloid pools in the leaves and stems declined rapidly, while the pool in the crown and roots tended to increase.

Distribution of locoweed toxin swainsonine in populations of Oxytropis lambertii.

Oxytropis lambertii has been considered to be one of the major locoweeds responsible for livestock poisoning on rangelands, but there has been much confusion as to its taxonomic identity. The objective of this study was to conduct a field survey of several populations of each of the three varieties [var. lambertii Pursh; var higelovii A. Gray; var. articulata (E. Greene) Barneby] to document the presence or absence of the locoweed toxin, swainsonine. Swainsonine was found at detectable levels (>0.001% dry weight) in only five populations of var. higelovii in the southwest portion of its distribution in southern Utah, Arizona, and southwestern New Mexico, USA. No swainsonine was detected in populations in the northeast areas of its distribution (eastern Utah, Colorado, northeastern New Mexico, USA). The other varieties, articulata and lambertii, also did not contain swainsonine. It is suspected that a plant fungal endophyte may be responsible for the high variability in swainsonine content in populations of O. lambertii.

Conditioning taste aversions to locoweed (Oxytropis sericea) in horses.

Locoweed (Oxytropis sericea) is a serious poisoning problem for horses grazing on infested rangelands in the western United States. Our objectives were to determine 1) whether lithium chloride or apomorphine would condition aversions to palatable foods, and at what doses, and 2) whether horses could be averted to fresh locoweed in a pen and grazing situation. Apomorphine was not an acceptable aversive agent because at the dose required to condition an aversion (> or = 0.17 mg/kg BW), apomorphine induced unacceptable behavioral effects. Lithium chloride given via stomach tube at 190 mg/kg BW conditioned strong and persistent aversions to palatable feeds with minor signs of distress. Pen and grazing tests were conducted in Colorado to determine if horses could be averted to fresh locoweed. Pen tests indicated that most horses (5/6) were completely averted from locoweed. Treated horses ate 34 g of fresh locoweed compared to 135 g for controls (P < 0.01) during three pen tests when offered 150 g per test. One horse (T) in the treatment group ate locoweed each time it was offered in the pen, but ate no locoweed while grazing. In the grazing trial, control horses averaged 8.6% of bites of locoweed (P < 0.01) during the grazing portion of the study, whereas treated horses averaged <0.5%. One treated horse (S) accounted for all consumption; he consumed 15% of his bites as locoweed in a grazing bout on d 2 of the field study. Thereafter, he was dosed a second time with lithium chloride and ate no locoweed in the subsequent 5 d. Three of six horses required two pairings of lithium chloride with fresh locoweed to condition a complete aversion. The results of this study indicate that horses can be averted from locoweed using lithium chloride as an aversive agent, and this may provide a management tool to reduce the risk of intoxication for horses grazing locoweed-infested rangeland.

Predicting toxicity of tall larkspur (Delphinium barbeyi): measurement of the variation in alkaloid concentration among plants and among years.

Tall larkspur (Delphinium barbeyi) is the principal mountain larkspur responsible for the majority of cattle deaths on mountain rangelands in western Colorado and central and southern Utah in the United States. Ten plants in each of two tall larkspur populations in the mountains near Ferron and Salina, Utah, were marked, and single stalks were harvested periodically through the growing season for 4 yr. Toxic alkaloid concentration [alkaloids containing the N-(methylsuccimimido)-anthranilik ester group] was determined by Fourier transform infrared (FTIR) spectroscopy. Individual larkspur plants varied in alkaloid concentrations, especially in early growth (14-38 mg/g). As the concentration declined over the growing season, variation among plants also declined. There were yearly differences in alkaloid concentration among individual plants (P < 0.01) and populations (P < 0.001), even after accounting for differences in phenological growth between years. Variables such as precipitation, temperature, days since snow melt, growing degree days (sum of mean temperature each day from snow melt), and plant height and weight were all considered in a Mallows Cp multiple regression selection procedure to predict alkaloid concentration. The mixed model procedure in SAS adjusted the regression equation for locations and years. Growing degree days was the best single predictor of alkaloid levels: In y = (3.581 - 0.00423 GDD), R2 = 0.85. Internal validation of this equation within individual years and locations from which the equation was developed, produced correlations between observed versus predicted values ranging from r = 0.73 to 0.93. External validations on nine other larkspur populations produced correlations ranging from r = 0.76 to 0.99. This predictive equation can provide a tool for ranchers and land managers to make management decisions of when to graze cattle in larkspur areas.

Analysis of swainsonine: extraction methods, detection, and measurement in populations of locoweeds (Oxytropis spp.).

An analytical method has been developed to measure the locoweed toxin, swainsonine, in locoweed plant material. Dry ground plant samples were extracted using a small-scale liquid/liquid extraction procedure followed by isolation of the swainsonine by solid phase extraction with a cation-exchange resin. Detection and quantitation of the swainsonine were accomplished using reversed phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry (LC-MS(2)). The limit of quantitation was estimated to be 0.001% swainsonine by weight in dry plant material, which corresponds to the lower threshold for toxicity of locoweeds. The method of analysis was applied to the analysis of Oxytropis sericea (white locoweed) and Oxytropis lambertii (Lambert locoweed) plant samples to measure the variability of individual plant swainsonine levels within populations and within species. Individual plant variability was found to be highly significant for both O. sericea and O. lambertii populations. The combined three-year mean swainsonine values taken from three populations of O. sericea ranged from 0.046% in Utah to 0.097% in a New Mexico population. Sixteen individual populations of O. lambertii were sampled from eight different U.S. states. Swainsonine was detected at levels >0.001% in only 5 of the 16 collection sites. Those populations of O. lambertii found to contain higher swainsonine levels were restricted to the most southern and western portion of its distribution, and all were identified as belonging to var. bigelovii, whereas var. articulata and var. lambertii samples contained swainsonine at levels <0.001%.

Influence of defoliation on toxic alkaloid concentration and alkaloid pools in tall larkspur.

This study was replicated at two locations in the mountains of central Utah. In 1997, ten uniform plants of tall larkspur (Delphinium barbeyi) in the early bud stage (40 cm in height) were selected at each site and clipped at 5 cm above soil level. In 1998, one stalk from each plant was harvested on a weekly basis; in 1999, one stalk was harvested at four times during its phenological development. Toxic and total alkaloid concentrations were measured and alkaloid pools in the entire stalk were calculated. Clipping reduced stalk height to less than 50 cm in 1998 and 65 cm in 1999, compared to over 100 cm in unclipped control plants. Alkaloid concentration was similar to control plants, but toxic alkaloid pools were 70% lower than control plants, because of the reduction in biomass of the stalks. Clipping reduced subsequent vigor and the amount of toxic and total alkaloids in tall larkspur.

Effects of locoweed (Oxytropis sericea) on reproduction in cows with a history of locoweed consumption.

Locoweed (Oxytropis sericea) was fed to 4 open cycling cows that had repeatedly consumed locoweed in previous grazing trails. They received locoweed at 20% of their diet for 30 d (0.68-0.76 mg swainsonine/kg/d). Locoweed induced an immediate rise in serum swainsonine (the locoweed toxin) and a concomitant drop in serum alpha-mannosidase activity in all cows accompanied by abnormal estrus behavior, increased estrous cycle lengths and failure to conceive. Serum progesterone (P4) profiles demonstrated that estrous cycles lengthened from an average of 19 d before locoweed feeding to an average of 34 d (range 24-43 d) while on locoweed. After locoweed feeding ceased, normal estrous cycles returned within an average of 14 d (range 7-25 d). Two of the 4 cows conceived on their first post-locoweed estrus at 7 and 25 d. The third cow bred twice at 13 and 31 d after lowoweed feeding stopped, and the fourth cow bred 3 times at 11, 31 and 52 d before conception occurred. Pregnancies in all 4 cows progressed normally to 7 mo gestation when locoweed was again fed at 20% of the diet for 40 d (gestation days 213 and 253) to 2/4 cows, 1 of which aborted 10 d after lowoweed feeding stopped (263 days gestation). The other cow fed lowoweed calved normally as did the 2 pregnancy control cows. Serum P4 and estradiol (E2) profiles during pregnancy appeared normal before, during and after locoweed feeding except in the cow that aborted, whose P4 declined and E2 increased prematurely. The general trend of serum prolactin was similar in locoweed-fed and control cows.

Ponderosa pine and broom snakeweed: poisonous plants that affect livestock.

Ponderosa pine (Pinus ponderosa) and the snakeweeds (Gutierrezia sarothrae and G. microcephala) are two groups of range plants that are poisonous to livestock. Ponderosa pine causes late-term abortions in cattle, and the snakeweeds are toxic and also cause abortions in cattle, sheep, and goats. Research is underway at the USDA-ARS-Poisonous Plants Research Laboratory to better understand livestock poisonings caused by grazing ponderosa pine needles and the snakeweeds and to provide methods of reducing losses to the livestock and supporting industries. This review includes the history of the problem, a brief description of the signs of poisoning, the research, to identify the chemical toxins, and current management practices on prevention of poisonings.

The pathogenesis and toxicokinetics of locoweed (Astragalus and Oxytropis spp.) poisoning in livestock.

Locoweed poisoning is a chronic disease that develops in livestock grazing for several weeks on certain Astragalus and Oxytropis spp. that contain the locoweed toxin, swainsonine. The purpose of this review is to present recent research on swainsonine toxicokinetics and locoweed-induced clinical and histologic lesions. Swainsonine inhibits cellular mannosidases resulting in lysosomal storage disease similar to genetic mannosidosis. Diagnosis of clinical poisoning is generally made by documenting exposure, identifying the neurologic signs, and analyzing serum for alpha-mannosidase activity and swainsonine. All tissues of poisoned animals contained swainsonine, and the clearance rates from most tissues was about 20 hours (T1/2 half life). The liver and kidney had longer rate of about 60 hours (T1/2). This suggests that poisoned animals should be allowed a 28-day withdrawal to insure complete swainsonine clearance. Poisoning results in vacuolation of most tissues that is most obvious in neurons and epithelial cells. Most of these histologic lesions resolved shortly after poisoning is discontinued; however, some neurologic changes are irreversible and permanent.

Locoweed grazing.

Locoweed is the most widespread poisonous plant problem in the western U. S. Eleven species of Astragalus and Oxytropis (and many varieties within these species) cause locoism. Many locoweed species are endemic and are restricted to a narrow niche or habitat. Other locoweed species experience extreme population cycles; the population explodes in wet years and dies off in drought. A few species, such as O. sericea, are relatively stable and cause persistent poisoning problems. Knowledge of where locoweeds grow and the environmental conditions when they become a threat is important to manage livestock and avoid poisoning. Locoweeds are relatively palatable. Many locoweeds are the first plants to begin growth in the spring and regrow in the fall. Livestock generally prefer the green-growing locoweeds to other forage that is dormant in the late fall, winter, and spring. The most effective management strategy is to deny livestock access to locoweeds during critical periods when they are more palatable than the associated forage. Herbicides can control existing locoweed populations and provide "safe" pastures for critical periods. However, locoweed seed in soil will germinate and re-establish when environmental condition are favorable. Good range management and wise grazing strategies can provide adequate forage for livestock and prevent them from grazing locoweed during non-critical periods of the year when it is relatively less palatable than associated forages.

Locoweeds: effects on reproduction in livestock.

Locoweeds (species of Oxytropis and Astragalus containing the toxin swainsonine) cause severe adverse effects on reproductive function in livestock. All aspects of reproduction can be affected: mating behavior and libido in males; estrus in females; abortion/embryonic loss of the fetus; and behavioral retardation of offspring. While much research has been done to describe and histologically characterize these effects, we have only begun to understand the magnitude of the problem, to define the mechanisms involved, or to develop strategies to prevent losses. Recent research has described the effects of locoweed ingestion in cycling cows and ewes. Briefly, feeding trials with locoweeds in cycling and pregnant cows have demonstrated ovarian dysfunction in a dose-dependent pattern, delayed estrus, extended estrous cycle length during the follicular and luteal phases, delayed conception (repeat breeders), and hydrops and abortion. Similar effects were observed in sheep. In rams, locoweed consumption altered breeding behavior, changed libido, and inhibited normal spermatogenesis. Neurological dysfunction also inhibited normal reproductive behavior, and some of these effects were permanent and progressive. In this article we briefly review the pathophysiological effects of locoweeds on reproduction.

Larkspur (Delphinium spp.) poisoning in livestock.

Larkspurs (Delphinium spp.) are toxic plants that contain numerous diterpenoid alkaloids which occur as one of two structural types: (1) lycotonine, and (2) 7,8-methylenedioxylycoctonine (MDL-type). Among the lycoctonine type alkaloids are three N-(methylsuccinimido) anthranoyllycoctonine (MSAL-type) alkaloids which appear to be most toxic: methyllycaconitine (MLA), 14-deacetylnudicauline (DAN), and nudicauline. An ester function at C-18 is an important structural requirement for toxicity. Intoxication results from neuromuscular paralysis, as nicotinic acetylcholine receptors in the muscle and brain are blocked by toxic alkaloids. Clinical signs include labored breathing, rapid and irregular heartbeat, muscular weakness, and collapse. Toxic alkaloid concentration generally declines in tall larkspurs with maturation, but alkaloid concentration varies over years and from plant to plant, and is of little use for predicting consumption by cattle. Knowledge of toxic alkaloid concentration is valuable for management purposes when cattle begin to eat larkspur. Cattle generally begin consuming tall larkspur after flowering racemes are elongated, and consumption increases as larkspur matures. Weather is also a major factor in cattle consumption, as cattle tend to eat more larkspur during or just after summer storms. Management options that may be useful for livestock producers include conditioning cattle to avoid larkspur (food aversion learning), grazing tall larkspur ranges before flowering (early grazing) and after seed shatter (late grazing), grazing sheep before cattle, herbicidal control of larkspur plants, and drug therapy for intoxicated animals. Some potentially fruitful research avenues include examining alkaloid chemistry in low and plains larkspurs, developing immunologic methods for analyzing larkspur alkaloids, developing drug therapy, and devising grazing regimes specifically for low and plains larkspur.

Conditioned food aversions: principles and practices, with special reference to social facilitation.

Conditioned food aversion is a powerful experimental tool to modify animal diets. We have also investigated it as a potential management tool to prevent livestock from grazing poisonous plants such as tall larkspur (Delphinium barbeyi), white locoweed (Oxytropis sericea) and ponderosa pine (Pinus ponderosa) on western US rangelands. The following principles pertain to increasing the strength and longevity of aversions: mature animals retain aversions better than young animals; novelty of the plant is important, although aversions can be created to familiar plants; LiCl is the most effective emetic, and the optimum dose for cattle is 200 mg/kg body weight; averted animals should be grazed separately from non-averted animals to avoid the influence of social facilitation which can rapidly extinguish aversions. Social facilitation is the most important factor preventing widespread application of aversive conditioning. When averted animals see other animals eat the target food they will sample it, and if there is no adverse reaction they will continue eating and extinguish the aversion. However, if averted animals can be grazed separately, aversions will persist. Aversive conditioning may provide an effective management tool to prevent animals from eating palatable poisonous plants that cause major economic loss.

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 > or = 0.2 mg/kg gained less weight than controls. After 16 days, animals receiving > or = 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 alpha-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 > or = 0.05 mg/kg; proximal convoluted renal and thyroid follicular epithelium at > or = 0.1 mg/kg; Purkinje's cells, Kupffer's cells, splenic and lymph node macrophages, and transitional epithelium of the urinary bladder at > or = 0.2 mg/kg; neurons of the basal ganglia, mesencephalon, and metencephalon at > or = 0.4 mg/kg; and cerebellar neurons and glia at > or = 0.8 mg/kg. Histologic lesions were generally found when tissue swainsonine concentrations were approximately 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.

The characterization and structure-activity evaluation of toxic norditerpenoid alkaloids from two Delphinium species.

A new N-(methylsuccinimido)anthranoyllycoctonine norditerpenoid alkaloid, geyerline, has been isolated and characterized from extracts of the poisonous larkspur Delphinium glaucum. A previously described norditerpenoid alkaloid, grandiflorine, has also been isolated from Delphinium geyeri. Both alkaloids are closely related structurally to the potent neurotoxin methyllycaconitine, established as the primary toxin in many larkspurs poisonous to cattle. Mouse bioassay tests showed grandiflorine to possess toxicity comparable to methyllycaconitine, while its synthetically derived monoacetate, grandiflorine acetate, and geyerline are significantly less toxic.

Tissue swainsonine clearance in sheep chronically poisoned with locoweed (Oxytropis sericea).

Locoweed poisoning is seen throughout the world and annually costs the livestock industry millions of dollars. Swainsonine inhibits lysosomal alpha-mannosidase and Golgi mannosidase II. Poisoned animals are lethargic, anorexic, emaciated, and have neurologic signs that range from subtle apprehension to seizures. Swainsonine is water-soluble, rapidly absorbed, and likely to be widely distributed in the tissues of poisoned animals. The purpose of this study was to quantify swainsonine in tissues of locoweed-poisoned sheep and determine the rate of swainsonine clearance from animal tissues. Twenty-four crossbred wethers were gavaged with ground Oxytropis sericea to obtain swainsonine doses of 1 mg swainsonine x kg(-1) BW x d(-1) for 30 d. After dosing, the sheep were killed on d 0, 1, 2, 3, 4, 6, 14, 30, 60, and 160. Animal weights and feed consumption were monitored. Serum was collected during dosing and withdrawal periods, and tissues were collected at necropsy. Serum swainsonine concentrations were determined using an alpha-mannosidase inhibition assay. Swainsonine concentrations in skeletal muscle, heart, brain, and serum were similar at approximately 250 ng/g. Clearance from these tissues was also similar, with half-lives (T(1/2)) of less than 20 h. Swainsonine at more than 2,000 ng/g, was detected in the liver, spleen, kidney, and pancreas. Clearance from liver, kidney, and pancreas was about T(1/2) 60 h. These findings imply that poisoned sheep have significant tissue swainsonine concentrations and animals exposed to locoweed should be withheld from slaughter for at least 25 d (10 T(1/2)) to ensure that the locoweed toxin has cleared from animal tissues and products.