Cyclopamine-induced synophthalmia in sheep: defining a critical window and toxicokinetic evaluation.

Cyclopamine, a steroidal alkaloid, from the plant Veratrum californicum is teratogenic, causing a range of different birth defects. The critical window for cyclopamine-induced synophthalmia formation has been reported to be gestational day (GD) 14. The objectives of this study were to better describe cyclopamine-induced craniofacial deformities, to better define the window of susceptibility to synophthalmia formation, and to characterize cyclopamine toxicokinetics in sheep. Ewes were dosed i.v. with purified cyclopamine for toxicokinetic analysis. Another four groups of ewes were dosed orally twice daily with 0.88 g/kg of V. californicum on GD 13, 14 or 15 or consecutively on GD days 13-15. Pregnancy and pre-partum fetal malformations were determined by ultrasound imaging on GD 60. At parturition lambs were assessed for gross malformations. The elimination half-life of cyclopamine in ewes was determined to be 1.1 +/- 0.1 h. The rapid clearance of cyclopamine indicates that ingestion of V. californicum must occur during a very narrow window for synophthalmia formation to occur. Ewes dosed with V. californicum on GD 13 or 14 had lambs with various craniofacial malformations including cyclopia, maxillary dysplasia and mandibular micrognathia. Ewes dosed on GD 15 delivered normal lambs. Ewes dosed consecutively on GD 13-15 were not pregnant at GD 60 and Veratrum-induced embryonic death was assumed to be the cause. Interestingly, lambs with cyclopia were smaller, under-developed and appeared premature even though their twin appeared fully developed. Initial evaluations suggest this was due to placental dysplasia.

White snakeroot poisoning in goats: Variations in toxicity with different plant chemotypes.

Tremetone and possibly other benzofuran ketones are believed to be the toxic compounds in white snakeroot. However, disease has not been reproduced with purified toxins and the concentrations of the benzofuran ketones in white snakeroot populations that cause toxicosis have not been documented. The objectives of this study were to compare the toxicity of seven plant populations, better characterize the clinical and pathologic changes of poisoning, and correlate intoxication with benzofuran ketone content. Four of the seven white snakeroot collections were toxic at the dose and duration used in the study. Affected goats became exercise intolerant, had significant serum enzyme changes and histological lesions in the large appendicular muscles. The incidence and severity of poisoning was not correlated with total doses of tremetone or total benzofuran ketone concentrations suggesting they may not be closely involved in producing toxicity and the possible involvement of an unidentified toxin. The results also demonstrate that white snakeroot populations vary chemically and toxicologically.

Elk (Cervus Canadensis) preference for feeds varying in selenium concentration.

Selenium-accumulator plants are reputed to be unpalatable to large ungulates. Elk (Cervus canadensis) populations in southeastern Idaho overlap with populations of Se-rich plants, but there is no information on the influence of plant Se concentration on elk dietary preferences. The objective of this study was to determine, under controlled conditions, the preference of elk for feeds varying in Se concentrations. Seven yearling female elk (128 ± 5 kg) were purchased from a commercial elk farm in southeastern Idaho and adapted to low-Se alfalfa pellets. Three feeding trials using pellets with predetermined Se concentrations were conducted. Alfalfa pellets were commercially made with the addition of Symphyotrichum ascendens (western aster) so that the pellets contained 0.4, 5, 20, 50, or 100 mg/kg (DM basis) Se. In trial 1, 5 Se-containing alfalfa pellets (0.4, 5, 20, 50, and 100 mg/kg Se) were offered for 10 d; trial 2 used 4 Se-containing alfalfa pellet choices (0.4, 20, 50, and 100 mg/kg), and trial 3 used 3 pellet choices (0.4, 50, and 100 mg/kg) for 6 d. In trial 1, consumption of the control pellets by elk was greater than each of the other pellet choices (P < 0.001). Similarly, consumption of the 5-mg/kg Se pellet differed from control pellet and all other Se-containing pellets (P < 0.0001). There were no differences (P > 0.50) in consumption of the 20-, 50-, or 100-mg/kg Se pellets. In trial 2, elk consumed more (P < 0.0001) of the control pellet than the 20-, 50-, and 100-mg/kg Se pellets. Similarly, elk consumed more (P < 0.0001) of the 20-mg/kg Se pellet than the 50- and 100-mg/kg Se pellets. There were no differences (P > 0.99) in elk consumption of the 50- and 100-mg/kg Se pellets. In trial 3, elk consumption of the control and 50- and 100-mg/kg Se pellets differed (P ≤ 0.03) from one another each day except that on d 1 and 2, where elk consumption of the 50- and 100-mg/kg Se pellets did not differ (P ≥ 0.32). Elk clearly discriminated against pellets with the highest Se concentrations when they were given pellets with differing Se concentrations. These results suggest that elk are not likely to select forages with high Se concentrations, particularly when high-Se plants are present in a rangeland situation with numerous other forage choices.

p53 alterations in plutonium-induced F344 rat lung tumors.

The tumor suppressor gene p53 plays a critical role in the cellular response to genetic damage caused by radiation. In addition, mutations in this gene are often encountered in cells in lung tumors resected from uranium miners whose exposure to radon daughters exceeded 450 working level months. However, most of these miners also smoked tobacco products. Thus whether this gene is of specific importance in lung cancer is unclear. In this study, aberrations in the p53 gene were investigated using an immunohistochemical assay on 38 lung tumors (26 squamous cell carcinomas, 9 adenocarcinomas and 3 adenosquamous carcinomas) from rats that had inhaled 239PuO2 aerosols. Only 2 tumors exhibited detectable levels of staining of p53 products; both were large, well-differentiated squamous cell carcinomas that had invaded the pleural cavity or mediastinum. Direct DNA sequence analysis was used to characterize the mutations in these two tumors, and both exhibited G-->A transition mutations. One tumor was mutated in the first position of codon 283, resulting in a lysine for glutamine substitution; the other tumor was mutated at the second position of codon 280, resulting in a histidine to arginine substitution. No alterations in exons 5-7 of the p53 gene were found in a representative sample of tumors that did not exhibit elevated levels of the protein by immunohistochemistry. Further, no detectable polymorphisms or deletions were observed within the rat p53 gene after Southern blot analysis of 18 randomly selected 239Pu-induced tumors. These results suggest that p53 mutations are relatively unimportant in the development of lung tumors induced in the rat by high-linear energy transfer radiation.

Expression of transforming growth factor alpha in plutonium-239-induced lung neoplasms in dogs: investigations of autocrine mechanisms of growth.

We have previously shown that 47% of radiation-induced lung neoplasms in dogs exhibit increased expression of epidermal growth factor receptor (EGFR). In this study, we investigated the expression of transforming growth factor alpha (TGF-alpha), a ligand for EGFR, to determine if an autocrine mechanism for growth stimulation was present in these tumors. As determined by immunohistochemistry, 59% (26/44) of the lung neoplasms examined had increased expression of TGF-alpha. Expression of TGF-alpha was not related to the etiology of the tumor, e.g., spontaneous or plutonium-induced; however, it was related to the phenotype of the tumor. Statistical analysis of the correlation of EGFR and TGF-alpha expression within the same tumor did not show a positive association; however, specific phenotypes did have statistically significant expression of EGFR or TGF-alpha, suggesting that overexpression of either the ligand or its receptor conferred a growth advantage to the neoplasm. Twenty-seven percent (32/117) of radiation-induced proliferative epithelial foci expressed TGF-alpha, and a portion of those foci (8/32) expressed both EGFR and TGF-alpha. This supports the hypothesis that these foci represent preneoplastic lesions, and suggests that those foci exhibiting increased expression of the growth factor or its receptor are at greater risk for progressing to neoplasia.

Expression of transforming growth factor alpha and epidermal growth factor receptor in rat lung neoplasms induced by plutonium-239.

Ninety-two rat lung proliferative lesions and neoplasms induced by inhaled 239PuO2 were evaluated for aberrant expression of transforming growth factor alpha (TGF-alpha) and epidermal growth factor receptor (EGFR). Expression of TGF-alpha protein, measured by immunohistochemistry, was higher in 94% of the squamous cell carcinomas and 87% of the foci of alveolar epithelial squamous metaplasia than that exhibited by the normal-appearing, adjacent lung parenchyma. In contrast, only 20% of adenocarcinomas and foci of epithelial hyperplasia expressed elevated levels of TGF-alpha. Many neoplasms expressing TGF-alpha also expressed excessive levels of EGFR mRNA. Southern and DNA slot blot analyses showed that the elevated EGFR expression was not due to amplification of the EGFR gene. These data suggest that increased amounts of TGF-alpha were early alterations in the progression of plutonium-induced squamous cell carcinoma, and these increases may occur in parallel with overexpression of the receptor for this growth factor. Together, these alterations create a potential autocrine loop for sustaining clonal expansion of cells initiated by high-LET radiation.

Development of enzyme-linked immunosorbent assays for toxic larkspur (Delphinium spp.) alkaloids.

Larkspur (Delphinium spp.) poisons thousands of cattle on western rangelands each year. Because poisoning does not cause specific lesions, and poisoned animals are rarely found before they die, definitively identifying poisoned animals is difficult. Additionally, toxin concentrations in larkspur plants vary with environment, plant, and location. Rapid, sensitive, and specific diagnostic techniques are needed to identify poisoned animals and to determine when and what plants are likely to poison livestock. In this study, three competitive inhibition enzyme-linked immunosorbent assays (CI-ELISA) for toxic larkspur alkaloids were developed. One assay is class-specific toward the N-(methylsuccinimido)anthranoyllycoctonine (MSAL) alkaloids, and two assays are specific for individual alkaloids. The assay with the lowest limit of detection had an I(50) of 191 pg with a limit of detection of 30.5 pg for methyllycaconitine. Spike and recovery studies using bovine blood and brain tissue ranged from 52 to 89%. These findings suggest that with additional development these techniques are likely to be excellent tools for diagnosing poisoned animals and identifying highly toxic plants.

Development of enzyme-linked immunosorbent assays for the hepatotoxic alkaloids riddelliine and riddelliine N-oxide.

Pyrrolizidine alkaloid-containing plants are widely distributed throughout the world and are particularly common in the genus Senecio. The structural types and concentrations of the alkaloids vary among plant species. In addition, within a species of plant, concentrations vary with environment and location. Many pyrrolizidine alkaloids are toxic and cause poisoning in livestock and in humans. Rapid, sensitive, and specific diagnostic techniques are needed to identify poisoned animals and to determine the particular plants and conditions under which livestock are likely to be poisoned. In this study, two competitive inhibition enzyme-linked immunosorbent assays for riddelliine, riddelliine N-oxide, and other closely related pyrrolizidine alkaloids were developed using polyclonal antibodies. One assay is class specific toward the free base forms of the pyrrolizidine alkaloids; the other assay showed cross-reactivity to both the free base and N-oxide forms of the alkaloids. The assay with the lowest limit of detection had an I(50) of 803.9 pg with a limit of detection of 47.5 pg for riddelliine. Spike and recovery studies for riddelliine in bovine blood ranged from 45 to 74%. The assay that showed cross-reactivity between the N-oxide and free base forms of the pyrrolizidine alkaloids allowed estimation of the total pyrrolizidine alkaloid content in Senecio riddellii in admixture with alfalfa. These findings suggest that these techniques will be excellent tools to diagnose poisoned animals and identify highly toxic plants.

Pyrrole detection and the pathologic progression of Cynoglossum officinale (houndstongue) poisoning in horses.

Houndstongue (Cynoglossum officinale), a noxious weed that contains pyrrolizidine alkaloids (PAs), infests pastures and fields in the western United States and Europe. The purpose of this study was to develop techniques to better diagnose PA poisoning and describe the progression of gross and microscopic lesions caused by houndstongue intoxication. Six horses were gavaged daily with a suspension of houndstongue containing 5 or 15 mg/kg total PA for 14 days. Two horses were treated similarly with ground alfalfa as controls. Liver biopsy samples and serum biochemical and hematologic values were evaluated biweekly. Within 7 days after dosing, horses treated with 15 mg/kg PA developed severe liver disease characterized by altered bile acid metabolism, elevated serum enzymes, and extensive hepatocellular necrosis with minimal periportal fibrosis and biliary hyperplasia. The condition of these animals continued to deteriorate, and they were euthanized. For several weeks after dosing, horses treated with 5 mg/kg PA were depressed, had transient elevations of serum enzymes and bile acids, and developed minimal periportal hepatocellular necrosis with fibrosis. The biochemical changes resolved by 6-8 weeks; however, the histologic disease persisted with extensive megalocytosis by week 14. Throughout the study, the rate of hepatocellular proliferation remained constant. Biliary cells had an increase in mitotic rate that correlated with the histologic changes. Hepatic tissue-bound pyrroles (PA metabolites) were identified in necropsy samples of treated animals using gas chromatography/mass spectrometry and photometrically with Ehrlich's reagent. These findings suggest that pyrrole extraction and identification are useful in documenting PA exposure and that houndstongue is extremely toxic to horses.

Serum alpha-mannosidase activity and the clinicopathologic alterations of locoweed (Astragalus mollissimus) intoxication in range cattle.

Subclinical intoxication of livestock with Astragalus and Oxytropis species (locoweeds) results in decreased animal feed conversion, reduced weight gains, and reproductive failure. Sensitive diagnostic methods to definitively diagnose and monitor intoxication are needed to minimize these losses and better manage locoweed-infested pastures and rangelands. Sera from cattle grazing locoweed were evaluated for alpha-mannosidase activity, serum biochemical values, electrolytes, and thyroid hormone concentrations. As the cows began to ingest locoweed, the mean serum alpha-mannosidase activities dropped significantly (400.0 microM to 72.5 microM). Changes in other serum chemistry values were less specific; however, individual animals (generally those ingesting more locoweed) had elevated levels of alkaline phosphatase (ALP), aspartate aminotransferase, and lactate dehydrogenase, with decreased serum total protein (5.8 +/- 0.8 g/dl) and albumin (2.3 +/- 0.3 g/dl). Mean serum thyroid concentrations (both T4 and T3) were lower in animals that were ingesting locoweed. The calculated swainsonine dose correlated statistically with serum alpha-mannosidase activity, ALP, albumin, Cl, CO2, and thyroid hormone T3. This correlation suggests that serum alpha-mannosidase activity along with potential changes in ALP, albumin, and thyroid hormone concentrations is a sensitive indicator of locoweed exposure and intoxication. These parameters may also be useful for monitoring intoxication and allowing subclinically affected cattle to be removed from infested areas before irreversible damage occurs.

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.

Operant analysis of chronic locoweed intoxication in sheep.

Five sheep were fed a 10% locoweed (Oxytropis sericea) pellet or alfalfa pellets for 3- to 5-wk periods to determine the effects of intermittent locoweed ingestion on operant responding; three controls were fed alfalfa pellets for 22 wk. Sheep were trained to respond to a multiple schedule with a fixed ratio (FR) 5 and fixed interval (FI) 50 s as major elements; performance was reinforced with rolled barley. Locoweed-treated sheep decreased (P < .05) FR response rate after 4 wk of locoweed feeding, but this decrease first appeared during the first recovery period (wk 6). The FR response rate of intoxicated sheep did not return to baseline during the remainder of the study and differed from controls during most of the study. Controls did not deviate (P > .05) from their FR baseline except during wk 2. Sheep did not stabilize on the FI component. As locoweed-treated sheep became progressively more intoxicated, they altered their pattern of FR responses, with longer post-reinforcement pauses, and a slower overall FR rate. Intoxicated sheep ingested an average of .21 mg swainsonine.kg-1.d-1. Overt signs of intoxication were noted when two sheep were stressed on wk 17. These two sheep had neuroviseral vacuolation typical of locoweed poisoning, whereas the three remaining locoweed-treated sheep that were euthanatized 5 wk later showed little histologic evidence of intoxication. Our findings indicate that "on-off" or cyclic grazing of locoweed ranges should be approached cautiously. Such a grazing program may be feasible because of the rapid resolution of histologic pathology; however, an initial toxic insult of 4 wk seems to be excessive, even at low doses, because sheep may exhibit persistent behavioral abnormalities that require > 6 wk to resolve.

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.

The toxicity and kinetics of larkspur alkaloid, methyllycaconitine, in mice.

Larkspur poisoning sporadically kills from 5 to 15% of the cattle on North American mountain rangelands. Of the 40 different diterpenoid larkspur alkaloids, the one that is thought to be responsible for much of the toxicity has been identified as methyllycaconitine (MLA). Little is known of MLA toxicokinetics or excretion. The purpose of this study was to further characterize the clinical effects of MLA toxicity in mice and determine the toxicokinetics of MLA excretion. Eight groups of mice were dosed intravenously with 2.0 mg/kg of BW of MLA, killed, and necropsied at 0, 1, 2, 5,10,15, 30, and 60 min after injection. Treated animals were reluctant to move, trembled, and developed dyspnea, muscular twitches, and convulsions. Within several minutes, the clinical signs abated and behavior slowly returned to normal over approximately 20 min. At necropsy serum, brain, liver, kidney, and skeletal muscle were collected and frozen. Blood and tissues were extracted and analyzed for MLA with HPLC and electron spray mass spectrometry. Blood MLA elimination followed a normal biphasic redistribution and excretion pattern (r = 0.99) with a K of elimination of 0.0376 and half-life of 18.4 min. Other tissues had similar clearance rates. These data indicate the MLA is rapidly distributed and excreted. In mice, the clinical effects of poisoning seem to affect the central nervous system, causing dyspnea and "explosive" muscular twitches and convulsions. Because livestock commonly eat larkspur at subclinical doses, they are likely to have larkspur alkaloids in many tissues. These results suggest that animals exposed to larkspur should rapidly excrete MLA (within several hours) and that the residues in animal tissues are not likely to be a problem if animals are given several days to allow toxin clearance.

Grazing of spotted locoweed (Astragalus lentiginosus) by cattle and horses in Arizona.

Spotted locoweed (Astragalus lentiginosus var. diphysus) is a toxic, perennial plant that may, if sufficient precipitation occurs, dominate the herbaceous vegetation of pinyon-juniper woodlands on the Colorado Plateau. Six cow/calf pairs and four horses grazed a 20-ha pasture with dense patches of locoweed in eastern Arizona during spring 1998. Locoweed density was 0.7 plants/m2 in the pasture. Locoweed averaged 30.4% NDF and 18.4% CP. Concentrations of the locoweed toxin, swainsonine, fluctuated from 1.25 to 2 mg/g in locoweed. Horses ate more (P < 0.01) bites of locoweed than did cows (15.4 and 5.1% of bites, respectively). Horses generally increased locoweed consumption over time since they ate approximately 5% of bites in the preflower stage compared with 25% of bites in the pod stage. Cattle consumed almost no locoweed (< 1% of bites) until the pod stage, when they increased consumption to 15% of bites. Horses were very avid (approximately 65 to 95% of bites) in selecting the small quantities (approximately 40 to 150 kg/ha) of available green grass, and it appeared that their propensity to eat scarce green forage influenced their locoweed consumption as well. Horses ate relatively little dry grass, even when it was abundant, whereas cattle ate large amounts of dry grass until green grasses became more abundant. Calves began eating locoweed on the same day as their dams and ate approximately 20% of their bites as locoweed. Serum concentrations of swainsonine were higher (P < 0.05) in horses than in cattle (433 vs. 170 ng/mL, respectively). Baseline swainsonine was zero in all animals, but swainsonine was rapidly increased to above 800 ng/mL in serum of horses as they ate locoweed. Horses exhibited depression after eating locoweed for about 2 wk; after 5 wk of exposure, horses became anorectic and behaviorally unstable. Although limited in scope, this study indicates that horses should not be exposed to spotted locoweed.

Evaluation of vaccination against methyllycaconitine toxicity in mice.

The purpose of this study was to determine whether larkspur toxins conjugated to protein carriers would promote active immunity in mice. Mice were injected with several larkspur toxin-protein conjugates or adjuvant alone to determine whether the resulting immunological response altered animal susceptibility to methyllycaconitine, the major toxic larkspur alkaloid. Although vaccinations increased the calculated lethal dose 50% (LD50) for intravenous methyllycaconitine toxicity, overlapping confidence intervals did not provide evidence of differences between the vaccinated and control groups. In the lycoctonine conjugate (LYC)-vaccinated group, mouse survival was related (P = 0.001) to serum titers for methyllycaconitine doses up to 4.5 mg/kg of body weight. When mice withlow antibody titers were removed from the vaccinated groups in which titer was related to survival, the recalculated LD50 estimates were 20% greater than the LD50 of the control group. However, the 95% confidence intervals of the recalculated LD50 groups overlapped with the control groups. Overall, these results suggest that vaccination altered methyllycaconitine toxicity in mice and that vaccination may be useful in decreasing the effects of larkspur toxins in animals. Additional studies are warranted to continue development of potential larkspur vaccines for livestock.

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.

Serum swainsonine concentration and alpha-mannosidase activity in cattle and sheep ingesting Oxytropis sericea and Astragalus lentiginosus (locoweeds).

Serum alpha-mannosidase activity and swainsonine concentration were determined in 4 cattle and 15 sheep (3 groups of 5 each) that were administered ground locoweed (Oxytropis sericea or Astragalus lentiginosus) containing swainsonine at dosages of approximately 0.8 mg/kg of body weight/d (cows, 30 days each) and 0, 1.0, and 1.5 mg/kg/d (sheep, 11 days each). The cattle developed mild clinical signs of locoism, including signs of depression, lethargy, and slight intention tremors. Clinical signs of toxicosis were not observed in the sheep. Within 24 hours of initial treatment, serum alpha-mannosidase activity in cows and sheep, measured by the release of 4-methylumbelliferone from an artificial substrate, was markedly decreased to 28 and 40 mumol of 4-methylumbelliferone/L, respectively. Mean serum alpha-mannosidase activity of control cows and sheep was 400 +/- 94 and 422 +/- 42 (mean +/- SD), respectively. In the treated animals, decreased serum alpha-mannosidase activities returned to normal or higher activities within 6 days after treatment was discontinued. Using a jack bean alpha-mannosidase assay, increased swainsonine activity (153, 209, and 381 ng/ml, respectively) was detected in the serum of cattle and of sheep in the high- and low-dose groups within 24 hours after treatment with locoweed. Swainsonine concentration remained high, with mean concentrations of 204, 432, and 395 ng/ml (cows and 2 sheep groups, respectively) during the treatment period. After treatment, swainsonine was rapidly cleared, with estimated serum half-life of 16.4, 17.6, and 20.3 hours (cows, and high- and low-dose sheep groups, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Reproductive toxicoses of food animals.

Reproductive dysfunction has many potential causes. In this article, the authors discuss toxicants that have been shown to affect reproduction, with emphasis on food-producing animals and fowl. The discussion is brief and written to provide a resource for clinicians, students, and scientists by focusing on toxicant-induced reproductive dysfunction and discussing the toxicant, source, clinical effects, and livestock species known or suspected to be affected.

Effect of natural toxins on reproduction.

Poisonous plants grow in most plant communities found on rangelands and pastures. They are one of the principal causes of economic loss to the livestock industry. One major costly effect is on reproduction, which includes birth defects, abortions, lengthened calving intervals, and interference with oogenesis, spermatogenesis, libido, and estrus. Those plants that cause wasting, temporary illness, and other such effects can adversely effect reproduction livestock.