ASTRAGALUS AND OXYTROPIS POISONING IN LIVESTOCK
Location: Poisonous Plant Research
Title: Acute toxicity of selenium compounds commonly found in selenium-accumulator plants
Submitted to: Poisoning by Plants, Mycotoxins, and Related Toxins
Publication Type: Book / Chapter
Publication Acceptance Date: April 28, 2010
Publication Date: May 1, 2011
Citation: Davis, T.Z., Stegelmeier, B.L., Green, B.T., Welch, K.D., Panter, K.E., Hall, J.O. 2011. Acute toxicity of selenium compounds commonly found in selenium-accumulator plants. In: Riet-Correa, F., Pfister, J., Schild, A.L., Wierenga, T., editors. Poisoning by Plants, Mycotoxins, and Related Toxins. Cambridge, MA. CAB International. 91:525-31.
Interpretive Summary: Selenium (Se) is an essential trace element required by livestock. Although essential, Se has a very narrow window between deficiency and toxicity. Selenium accumulating plants such as Astragalus spp., Stanleya pinnata, and Aster spp. are commonly found in various regions of the western United States. Primary selenium accumulator plants can store up to 13,000 ppm Se, as predominantly selenate and methylselenocysteine (MeSeCys) and be extremely toxic to livestock or wildlife that graze them. During a recent four year period, over 500 sheep were poisoned on selenium accumulator plants (predominantly western aster) growing on reclaimed mine sites in southeastern Idaho. The objective of this study was to compare the acute toxicosis and toxicokinetics of Se in lambs orally dosed with selenate, MeSeCys, selenomethionine (the most common form of Se in non-primary accumulator forages), and the selenium-accumulator plant western aster. The different forms of Se caused different severity of clinical signs in addition to different txociokinetics in the respired air, serum and whole blood. Therefore, when diagnosing selenium toxicity by measuring Se concentrations in respired air, whole blood or tissues it is important to know the form of Se that was ingested because respiratory elimination, tissue accumulation, and serum and whole blood kinetics are very different for different selenium forms.
Selenium (Se) accumulating plants, such as Astragalus spp. and Aster spp., can accumulate up to 8,000 to 13,000 ppm selenium and can cause acute toxicity when consumed by livestock or wildlife. Recent research has shown that much of the selenium in some Se-accumulating plants is stored as selenate or Se-methylselenocysteine (MeSeCys). The objective of this study was to compare the acute toxicosis and toxicokinetics of Se in lambs orally dosed with selenate, MeSeCys, selenomethionine (the most common form of Se in non-primary accumulator forages), and the selenium-accumulator plant western aster. Lambs were administered a single intraruminal dose of 0, 1, 2, 3, 4, or 6 mg of Se / kg of bodyweight as selenate, MeSeCys, selenomethionine or Se in western aster. Within 12 hours of dosing, some lambs became depressed, reluctant to move, rested with their necks stretched out, had decreased appetite, and tachypnea. Several lambs died during the first 48 hours after dosing. All lambs that did not die within the initial 48 hours recovered and appeared healthy by 72 hours. The Se concentrations in the serum of lambs dosed with MeSeCys, selenomethionine, western aster, and selenate were 3.078 ± 0.444, 3.193 ± 0.337, 2.970 ± 0.255, 2.847 ± 0.237 ppm and peaked at 4, 8, 12, and 8 hours post-dosing, respectively. Selenium concentrations in whole blood in lambs dosed with MeSeCys, selenomethionine, western aster, and selenate were 6.436 ± 1.521, 2.547 ± 0.098, 1.876 ± 0.330 and 1.892 ± 0.218 ppm and peaked at 6, 6, 12, and 8 hours post-dosing, respectively. The Se concentrations in heart, liver, kidney and lung are also reported for sheep at the time of death or at seven days post-dosing for those sheep that did not die from acute Se poisoing.