Location: Poisonous Plant ResearchTitle: Rumen microorganisms decrease bioavailability of inorganic selenium supplements Author
|Galbraith, M - Oregon State University|
|Vorachek, W - Oregon State University|
|Estill, C - Oregon State University|
|Whanger, P - Oregon State University|
|Bobe, G - Oregon State University|
|Davis, Thomas - Zane|
|Hall, J - Oregon State University|
Submitted to: Biological Trace Element Research
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/27/2015
Publication Date: 6/1/2016
Publication URL: http://handle.nal.usda.gov/10113/63233
Citation: Galbraith, M.L., Vorachek, W.R., Estill, C.T., Whanger, P.D., Bobe, G., Davis, T.Z., Hall, J.A. 2016. Rumen microorganisms decrease bioavailability of inorganic selenium supplements. Biological Trace Element Research. 171(2):338-343. Interpretive Summary: Selenium (Se) has been recognized for years as an essential trace element for ruminant animals. In general, the majority of livestock raised in low-Se regions do not receive sufficient dietary Se for optimum health. In the United States a survey of state veterinarians and state veterinary diagnostic labs revealed that Se deficiency diseases were diagnosed in 46 states and reported to be an important livestock problem in 36 states. Severe Se deficiency in ruminants results in nutritional myodegeneration known as 'white muscle disease', additionally insufficient Se intake has been implicated as the cause of many Se-responsive disorders. Since the Se status of plants, animals, and humans varies markedly around the world as a result of different geological conditions it is common to supplement livestock with Se-containing supplements. The purpose of this study was to determine if there were differences in metabolism of various selenocompounds by rumen microorganisms. The results demonstrated that organic Se as selenomethionine was incorporated to a greater extent into rumen microorganisms than inorganic Se sources and resulted in less elemental Se formation. Decreased oral bioavailability of inorganic Se compared with Se-yeast noted in our whole animal studies may be explained by these ex-vivo results showing increased elemental Se formation and decreased microbial incorporation of selenomethionine. Consumption of Se-fertilized forage as a source of organic Se provides an attractive alternative to inorganic Se supplements, because organic selenomethionine in forage would be better incorporated into rumen microorganisms and would result in less elemental Se formation.
Technical Abstract: Despite the availaility of selenium (Se)-enriched trace mineral supplements, we have observed low Se status in cattle and sheep offered traditional inorganic Se supplements. Reasons for this may include inadequate intake or low bioavailability of inorganic Se sources. The objective of this study was to determine whether rumen microorganisms (RMO) alter the bioavailability of Se sources commonly used in Se supplements. Rumen microorganisms were isolated from ewes (n=4) and incubated ex vivo with no Se (control), with inorganic Na selenite or Na selenate, or with organic selenomethionine (SeMet). Total Se incorporated into RMO and the anmount of elemental Se formed were determined under equivalent conditions. Incorporation of Se from Na selenite, Na selenate, or SeMet into RMO was measured as fold change compared with control (no added Se). Incorporation of Se into microbial mass was greater for SeMet (13.2 fold greater than no-Se control) compared with inorganic Se supplements (P=0.02); no differences were observed between inorganic Na selenate (3.3 fold greater than no-Se control) and Na selenite (3.5 fold greater than no-Se control; P=0.97). Formation of non-bioavailable, elemental Se was less for RMO incubated with SeMet compared with inorganic Se sources (P=0.006); no differences were observed between Na selenate and Na selenite (P=0.11). Decreased oral bioavailability of inorganic Se compared with organic Se-yeast noted in our previously reported in vivo animal studies is most likely explained by decreased microbial incorporation of Se and increased formation of elemental Se by RMO.