Pathology of experimentally induced chronic selenosis (alkali disease) in yearling cattle

Toxicity of repeated oral intake of organic selenium, inorganic selenium, and selenium nanoparticles: A review

BACKGROUND

To protect from toxicity at supra-essential doses of selenium, it is important to determine dose levels at which adverse effects occur.

METHODS

We identified relevant literature on the repeated dosage of selenium and extracted dose descriptors on reported endpoints, except on genotoxicity/carcinogenicity.

RESULTS

Selenium forms with toxicological data were organic ones: selenomethionine, selenocystine/selenocysteine; and inorganic ones, including selenite (SeO₃^2-), selenate (SeO₄^2-), selenium sulphide (SeS₂), selenide (Se^2-) and selenium nanoparticles. Clinical signs of selenium toxicity in humans include a garlicky-smelling breath, hair loss, and nail changes. One human study showed increased mortality following daily ingestion of 300 µg Se per day for 5 years, equal to a lowest-observed-adverse-effect level (LOAEL) of ∼4.3 µg/kg bw/days. The corresponding no-observed-adverse-effect level (NOAEL) was ∼2.9 µg Se/kg bw/day. One study reported an increased risk of type 2 diabetes after ∼2.9 µg Se/kg bw/day, but other studies with similar doses found no increases in mortality or incidence of type 2 diabetes. NOAELs on affected body weight in animal studies were 0.24-1.2 mg Se/kg bw/day. Other endpoints of selenium toxicity in animals include hepatotoxicity with a NOAEL as low as 2 µg/kg bw/day in rats, as well as gastrointestinal, cardiovascular, and reproductive toxicities with NOAELs of 0.6 (gastrointestinal), 0.08, and 0.4 (cardiovascular) and ≥ 0.04 mg Se/kg bw/day (reproductive), respectively.

CONCLUSIONS

Dose descriptors describing selenium toxicity were as low as 2-3 µg Se/kg bw/day.

Biomarkers and their potential for detecting livestock plant poisonings in Western North America

The United States National Cancer Institute defines a biomarker as: "A biological molecule found in blood, other body fluids, or tissues that is a sign of a normal or abnormal process, or of a condition or disease." In Veterinary Medicine, biomarkers associated with plant poisonings of livestock have great utility. Since grazing livestock poisoned by toxic plants are often found dead, biomarkers of plant poisoning allow for a more rapid postmortem diagnosis and response to prevent further deaths. The presence and concentration of toxins in poisonous plants are biomarkers of risk for livestock poisoning that can be measured by the chemical analysis of plant material. More difficult is, the detection of plant toxins or biomarkers in biological samples from intoxicated or deceased animals. The purpose of this article is to review potential biomarkers of plant poisoning in grazing livestock in the Western North America including recently investigated non-invasive sampling techniques. Plants discussed include larkspur, lupine, water hemlock, swainsonine-containing plants, selenium-containing plants, and pyrrolizidine alkaloid containing plants. Other factors such as animal age and sex that affect plant biomarker concentrations in vivo are also discussed.

Scientific opinion on the tolerable upper intake level for selenium

Following a request from the European Commission, the EFSA Panel on Nutrition, Novel Foods and Food Allergens (NDA) was asked to deliver a scientific opinion on the tolerable upper intake level (UL) for selenium. Systematic reviews of the literature were conducted to identify evidence regarding excess selenium intake and clinical effects and potential biomarkers of effect, risk of chronic diseases and impaired neuropsychological development in humans. Alopecia, as an early observable feature and a well-established adverse effect of excess selenium exposure, is selected as the critical endpoint on which to base a UL for selenium. A lowest-observed-adverse-effect-level (LOAEL) of 330 μg/day is identified from a large randomised controlled trial in humans (the Selenium and Vitamin E Cancer Prevention Trial (SELECT)), to which an uncertainty factor of 1.3 is applied. A UL of 255 μg/day is established for adult men and women (including pregnant and lactating women). ULs for children are derived from the UL for adults using allometric scaling (body weight0.75). Based on available intake data, adult consumers are unlikely to exceed the UL, except for regular users of food supplements containing high daily doses of selenium or regular consumers of Brazil nuts. No risk has been reported with the current levels of selenium intake in European countries from food (excluding food supplements) in toddlers and children, and selenium intake arising from the natural content of foods does not raise reasons for concern. Selenium-containing supplements in toddlers and children should be used with caution, based on individual needs.

Ramaria flavo-brunnescens mushroom poisoning in South America: A comprehensive review

Ramaria flavo-brunnescens is a mushroom that grows in eucalyptus forests causing poisoning in cattle, sheep and, with less frequency, in horses and pigs. It causes ulcerative and gangrenous lesions in the skin, tongue and esophagus, and loss of hairs of the tip of the tail. Nervous signs are occasionally observed in sheep. This review aims to update the knowledge about poisoning by R. flavo-brunnescens in cattle and sheep in South America. Articles published as of 1950 were retrieved, and the epidemiological data, clinical signs, pathologies, and data on the pathogenesis of intoxication were reviewed including the most recent data on possible modes of action of the active ingredient(s) of R. flavo-brunnescens.

Effects of Selenium Supplementation on Rumen Microbiota, Rumen Fermentation, and Apparent Nutrient Digestibility of Ruminant Animals: A Review

Enzymes excreted by rumen microbiome facilitate the conversion of ingested plant materials into major nutrients (e.g., volatile fatty acids (VFA) and microbial proteins) required for animal growth. Diet, animal age, and health affect the structure of the rumen microbial community. Pathogenic organisms in the rumen negatively affect fermentation processes in favor of energy loss and animal deprivation of nutrients in ingested feed. Drawing from the ban on antibiotic use during the last decade, the livestock industry has been focused on increasing rumen microbial nutrient supply to ruminants through the use of natural supplements that are capable of promoting the activity of beneficial rumen microflora. Selenium (Se) is a trace mineral commonly used as a supplement to regulate animal metabolism. However, a clear understanding of its effects on rumen microbial composition and rumen fermentation is not available. This review summarized the available literature for the effects of Se on specific rumen microorganisms along with consequences for rumen fermentation and digestibility. Some positive effects on total VFA, the molar proportion of propionate, acetate to propionate ratio, ruminal NH3-N, pH, enzymatic activity, ruminal microbiome composition, and digestibility were recorded. Because Se nanoparticles (SeNPs) were more effective than other forms of Se, more studies are needed to compare the effectiveness of synthetic SeNPs and lactic acid bacteria enriched with sodium selenite as a biological source of SeNPs and probiotics. Future studies also need to evaluate the effect of dietary Se on methane emissions.

Toxic Wasting Disorders in Sheep

Simple Summary

There are several substances, either inorganic or organic that may be toxic for sheep. Intoxications by some of these substances have an acute clinical course with specific signs and lesions that may guide the diagnostic procedures. However, there are other insidious, subacute to chronic presentations, usually related to continuous intake of the toxic substance over long periods of time, that may present with emaciation, ill-thrift, and/or poor external aspect. In such scenarios, diagnosis may be challenging and should be achieved through a combination of history of exposure, subtle gross and histological findings (if present), and available ancillary tests.

Abstract

Infectious and parasitic agents have been frequently associated with debilitating and wasting conditions in sheep. The prevalence of these agents has probably undermined the role of toxic causes as contributors to such disorders. In addition, many of these intoxications frequently produce acute clinical disease with specific and characteristic lesions, thus a causal relationship with the toxic substance may be relatively easy to establish. However, persistent exposure to some of these organic or inorganic toxic substances may lead to emaciation, ill-thrift, and poor external aspect. The anti-nutritional factors and alkaloids of several plants, including pyrrolizidine alkaloids, among others, have also been associated with emaciation and/or poor general performance in sheep flocks. In this review, some of these disorders are discussed with an emphasis on clinical signs and lesions, relevant diagnostic aspects, and available therapeutic approaches. In most cases, demonstrating a history of exposure should be one of the most relevant aspects of the diagnostic approach, and removing the animals from the toxic source is the cornerstone of the majority of the treatment strategies.

Water Quality for Cattle: Metalloid and Metal Contamination of Water

Water is the most important nutrient for rangeland livestock. However, competition with municipalities, industry, and other water users often results in grazing livestock being forced to use water supplies that are less than perfect. Surface water in western rangleands are often contaminated by mineral extraction, irrigation runoff and other human activities. Mineral contaminants in drinking water are additive with similar contaminants in feedstuffs. The goal of this article is to provide producers and veterinarians with the basic background to make informed decisions about whether a given water supply is "safe" for livestock.

Evaluating Mineral Status in Ruminant Livestock

Determining mineral status of production animals is important when developing an optimum health program. Nutrition is the largest expense in food animal production and has the greatest impact on health and productivity of the animals. Knowing the bioavailability of minerals in the diet is difficult. Evaluating fluid or tissues from animals is the optimum method to determine bioavailability. Evaluating the diet provides some information. Serum/blood or liver from the animal needs to be analyzed to determine bioavailability of vitamin and minerals in the diet. This article reviews how to sample and the function of these minerals in cattle.

Selenosis in Ruminants

Selenium (Se) is a metalloid that exists as a red amorphous powder, reddish crystal, silver-gray crystal, or brown-black solid. Its potency as a nutrient and a toxicant is such that few people have seen the pure element. It is easy to lose sight of the narrow margin between too little and too much. The most common cause of selenosis is accidental or intentional overuse of supplements. Many target organs and effects of Se toxicity are similar to those of Se deficiency, so laboratory confirmation is necessary. Prevention consists of minimizing exposure to seleniferous feedstuffs and optimizing dietary factors that might aggravate selenosis.

Effects of soft electrophiles on selenium physiology

This review examines the effects of neurotoxic electrophiles on selenium (Se) metabolism. Selenium-dependent enzymes depend on the unique and elite functions of selenocysteine (Sec), the 21st proteinogenic amino acid, to perform their biochemical roles. Humans possess 25 selenoprotein genes, ~ half of which are enzymes (selenoenzymes) required for preventing, controlling, or reversing oxidative damage, while others participate in regulating calcium metabolism, thyroid hormone status, protein folding, cytoskeletal structure, Sec synthesis and Se transport. While selenoproteins are expressed in tissue dependent distributions and levels in all cells of all vertebrates, they are particularly important in brain development, health, and functions. As the most potent intracellular nucleophile, Sec is subject to binding by mercury (Hg) and other electron poor soft neurotoxic electrophiles. Epidemiological and environmental studies of the effects of exposures to methyl-Hg (CH₃Hg⁺), elemental Hg (Hg°), and/or other metallic/organic neurotoxic soft electrophiles need to consider the concomitant effects of all members of this class of toxicants in relation to the Se status of their study populations. The contributions of individual electrophiles' discrete and cooperative rates of Se sequestration need to be evaluated in relation to tissue Se reserves of the exposed populations to identify sensitive subgroups which may be at accentuated risk due to poor Se status. Additional study is required to examine possibilities of inherited, acquired, or degenerative neurological disorders of Se homeostasis that may influence vulnerability to soft electrophile exposures. Investigations of soft electrophile toxicity will be enhanced by considering the concomitant effects of combined exposures on tissue Se-availability in relation to pathological consequences during fetal development or in relation to etiologies of neurological disorders and neurodegenerative diseases. Since selenoenzymes are molecular "targets" of soft electrophiles, concomitant evaluation of aggregate exposures to these toxicants in relation to dietary Se intakes will assist regulatory agencies in their goals of improving and protecting public health.

Experimentally Induced Selenosis in Yellow-Bellied Slider Turtles ( Trachemys scripta scripta)

Selenosis, or selenium toxicosis, occurs in wildlife and livestock, usually because of excessive intake of selenium via selenium-containing plants. Although it is known that wild slider turtles can accumulate large amounts of selenium, little is known about how selenium exposure may affect these reptiles. In this study, the authors report histopathologic changes in yellow-bellied sliders ( Trachemys scripta scripta) caused by experimental exposure to selenomethionine. Microscopic changes in kidney and claw tissue were most significant and resembled those reported in birds. Turtles in the selenium treatment groups had acute tubular degeneration and regeneration in the kidney, with hyaline droplets in the high-dose animals, and changes in the claws ranging from epidermal hyperplasia with disorganization and intercellular edema to ulceration, and accumulation of seroheterophilic exudate between the epidermis and cornified layer. Although selenium burdens in this study are comparable with values found in wild slider turtles, more data are needed to determine if similar histopathologic abnormalities arise in wild animals exposed to high levels of selenium.

Weaned beef calves fed selenium-biofortified alfalfa hay have an enriched nasal microbiota compared with healthy controls

Selenium (Se) is an essential trace mineral important for immune function and overall health of cattle. The nasopharyngeal microbiota in cattle plays an important role in overall respiratory health, especially when stresses associated with weaning, transport, and adaptation to a feedlot affect the normal respiratory defenses. Recent evidence suggests that cattle diagnosed with bovine respiratory disease complex have significantly less bacterial diversity. The objective of this study was to determine whether feeding weaned beef calves Se-enriched alfalfa (Medicago sativa) hay for 9 weeks in a preconditioning program prior to entering the feedlot alters nasal microbiota. Recently weaned beef calves (n = 45) were blocked by sex and body weight, randomly assigned to 3 treatment groups with 3 pens of 5 calves per treatment group, and fed an alfalfa hay based diet for 9 weeks. Alfalfa hay was harvested from fields fertilized with sodium selenate at a rate of 0, 45.0 or 89.9 g Se/ha. Blood samples were collected biweekly and analyzed for whole-blood Se concentrations. Nasal swabs were collected during week 9 from one or two calves from each pen (total n = 16). Calculated Se intake from dietary sources was 3.0, 15.6, and 32.2 mg Se/head/day for calves consuming alfalfa hay with Se concentrations of 0.34 to 2.42 and 5.17 mg Se/kg dry matter, respectively. Whole-blood Se concentrations after 8 weeks of feeding Se-fertilized alfalfa hay were dependent upon Se-application rates (0, 45.0, or 89.9 g Se/ha) and were 155, 345, and 504 ng/mL (P_Linear < 0.0001). Microbial DNA was extracted from nasal swabs and amplified and sequenced. Alpha rarefaction curves comparing the species richness (observed OTUs) and overall diversity (Chao1, Observed OTU, and Shannon index) between calves fed selenium-biofortified alfalfa hay compared with control calves showed that Se-supplementation tended to be associated with an enriched nasal microbiota. ANOSIM of unweighted UniFrac distances showed that calves fed high Se-biofortified alfalfa hay clustered separately when compared with control calves in the PCoA plot (R = 0.216, P = 0.04). The bacterial orders Lactobacillales and Flavobacteriales were increased in healthy control calves compared with Clostridiales and Bacteroidales being increased in calves fed Se-biofortified alfalfa hay. Although there were strong trends, no significant differences were noted for any of the bacterial taxa. Based upon these findings, we suggest that weaned beef calves fed Se-biofortified hay tend to have an enriched nasal microbiota. Feeding Se-biofortified alfalfa hay to weaned beef calves prior to entering the feedlot is a strategy for increasing nasopharyngeal microbial diversity.

A new oxygen modification cyclooctaoxygen binds to nucleic acids as sodium crown complex

BACKGROUND

Oxygen exists in two gaseous and six solid allotropic modifications. An additional allotropic modification of oxygen, the cyclooctaoxygen, was predicted to exist in 1990.

METHODS

Cyclooctaoxygen sodium was synthesized in vitro from atmospheric oxygen, or catalase effect-generated oxygen, under catalysis of cytosine nucleosides and either ninhydrin or eukaryotic low-molecular weight RNA. Thin-layer chromatographic mobility shift assays were applied on specific nucleic acids and the cyclooctaoxygen sodium complex.

RESULTS

We report the first synthesis and characterization of cyclooctaoxygen as its sodium crown complex, isolated in the form of three cytosine nucleoside hydrochloride complexes. The cationic cyclooctaoxygen sodium complex is shown to bind to nucleic acids (RNA and DNA), to associate with single-stranded DNA and spermine phosphate, and to be essentially non-toxic to cultured mammalian cells at 0.1-1.0mM concentration.

CONCLUSIONS

We postulate that cyclooctaoxygen is formed in most eukaryotic cells in vivo from dihydrogen peroxide in a catalase reaction catalyzed by cytidine and RNA. A molecular biological model is deduced for a first epigenetic shell of eukaryotic in vivo DNA. This model incorporates an epigenetic explanation for the interactions of the essential micronutrient selenium (as selenite) with eukaryotic in vivo DNA.

GENERAL SIGNIFICANCE

Since the sperminium phosphate/cyclooctaoxygen sodium complex is calculated to cover the active regions (2.6%) of bovine lymphocyte interphase genome, and 12.4% of murine enterocyte mitotic chromatin, we propose that the sperminium phosphate/cyclooctaoxygen sodium complex coverage of nucleic acids is essential to eukaryotic gene regulation and promoted proto-eukaryotic evolution.

Selenium and mercury concentrations in harbor seals (Phoca vitulina) from central California: health implications in an urbanized estuary

We measured total selenium and total mercury concentrations ([TSe] and [THg]) in hair (n=138) and blood (n=73) of harbor seals (Phoca vitulina) from California to assess variation by geography and sex, and inferred feeding relationships based on carbon, nitrogen, and sulfur stable isotopes. Harbor seals from Hg-contaminated sites had significantly greater [THg], and lesser [TSe] and TSe:THg molar ratios than seals from a relatively uncontaminated site. Males had significantly greater [THg] than females at all locations. Sulfur stable isotope values explained approximately 25% of the variability in [THg], indicating increased Hg exposure for seals with a greater use of estuarine prey species. Decreased [TSe] in harbor seals from Hg-contaminated regions may indicate a relative Se deficiency to mitigate the toxic effects of Hg. Further investigation into the Se status and the potential negative impact of Hg on harbor seals from Hg-contaminated sites is warranted.

Characterization of cytosolic glutathione peroxidase and phospholipid-hydroperoxide glutathione peroxidase genes in rainbow trout (Oncorhynchus mykiss) and their modulation by in vitro selenium exposure

Selenium (Se) is an oligonutrient with both essential biological functions and recognized harmful effects. As the selenocysteine (SeCys) amino acid, selenium is integrated in several Se-containing proteins (selenoproteins), many of which are fundamental for cell homeostasis. Nevertheless, selenium may exert toxic effects at levels marginally above those required, mainly through the generation of reactive oxygen species (ROS). The selenium chemical speciation can strongly affect the bioavailability of this metal and its impact on metabolism, dictating the levels that can be beneficial or detrimental towards an organism. Glutathione peroxidase (GPxs) is the largest and the most studied selenoprotein family. Cytosolic glutathione peroxidase (cGPx, GPx1) and phospholipid hydroperoxide glutathione peroxidase (PHGPx, GPx4) are widely distributed throughout tissues, and play a pivotal role in regulating the oxidative status in the cell. In this study we have cloned GPx1 and GPx4 genes in rainbow trout (Oncorhynchus mykiss). The constitutive mRNA expression of these GPx genes was examined in 18 trout tissues and their responsiveness to Se availability was analysed using a rainbow trout liver cell line (RTL). An inorganic (sodium selenite, Na2SeO3) and organic (selenocysteine, Cys-Se-Se-Cys) selenocompound have been used as Se sources. GPx1 activity was also tested to verify the impact of transcript changes on the enzymatic function of these molecules. To understand if the results obtained from the transcript expression analysis were due to Se bioavailability or generation of ROS, the cytoxicity of the two selenocompounds was tested by measuring the impact of Se on cell membrane integrity. Lastly, Se availability was quantified by mass spectrophotometry to determine the amount of Se in the cell culture media, the Se background due to the foetal calf serum supplement and the contribution from the two selenocompounds used in the treatments. Three isoforms of genes for both GPx1 (GPx1a, 1b1 and 1b2) and GPx4 (GPx4a1, a2 and b) have been identified. The discovery of a third gene encoding for GPx1 and GPx4 hints that salmonids may have the biggest selenoproteome amongst all vertebrates. Transcripts of GPx4 genes were more highly expressed in most tissues examined in vivo (except blood, head kidney and spleen), whereas those of the GPx1 genes were more responsive to selenium exposure in vitro, especially to the organic form. Interestingly, GPx1a was the most sensitive to selenium availability in non stressful conditions, whereas GPx1b1 and GPx1b2 were highly induced by exposure to selenium levels that had some toxic effects on the cells. Although the different concentrations tested of the two selenocompounds modulate GPx1 transcript expression to various degrees, no significant change of GPx1 enzymatic activity was detectable. Our results lead us to conclude that trout GPx1 transcripts expression level may represent a sensitive biomarker for selenium intake, helping to evaluate if selenium concentration and chemical speciation impact on cell homeostasis.

Grazing as an alternative for utilization of saline-sodic soils in the San Joaquin Valley: selenium accretion and performance of beef heifers

Two experiments were conducted to evaluate Se accumulation and health of non-pregnant, non-breeding beef cattle grazing on forages with a high Se content due to irrigation with saline drainage water. Heifers grazed experimental pastures of "Jose" tall wheatgrass (TWG; Thinopyrum ponticum var. "Jose") and creeping wildrye (CWR; Leymus triticoides var. "Rio") for 190 days in Experiment 1 (2007) and for 165 days in Experiment 2 (2008). In experiment 1, mean Se concentrations were similar in TWG and CWR herbage (4.0 versus 3.7 ± 0.26 mg/kg dry weight; p=0.34) as was crude protein (113 versus 114 ± 7.9 g/kg dry weight; p=0.94). Concentrations of Se in blood increased by 300% during the grazing period, and were similar for heifers grazing the TWG or CWR pastures (0.94 versus 0.87 ± 0.03 mg/kg; p=0.89). Heifers grazing on TWG gained more body weight than did heifers grazing on CWR (0.59 versus 0.27 ± 0.07 kg/days; p<0.01). In experiment 2, concentration of Se (4.0 versus 2.8 mg/kg ± 0.19 mg/kg dry weight; p<0.01) and crude protein (79 versus 90 ± 5.6 g/kg dry weight; p<0.01) differed, for TWG and CWR, respectively. Within 20 days, Se concentrations in blood had increased by 300% and by nearly 200% in heifers grazing on TWG or CWR. All data cited are least square means ± standard error of the mean. Data from our two grazing seasons are consistent in demonstrating the safety of grazing beef cattle for a period of up to 6 months on TWG and CWR forages having high levels of Se due to irrigation with saline drainage water. This suggests that forage production using saline drainage water is a viable alternative for saline soils with limited potential for producing high value, salt-sensitive, crops.

Dietary selenium for the mitigation of radiation injury: effects of selenium dose escalation and timing of supplementation

We recently reported that daily dietary supplementation with 100 µg selenium (a dose exceeding a rat's nutritional requirement by about 33-fold) initiated immediately after total-body irradiation (TBI) and maintained for 21 weeks mitigates radiation nephropathy in a rat model as indicated by blood urea nitrogen (BUN) levels and histopathological criteria (Radiat Res. 2009; 17:368-73). In this follow-up study, we explored the risks and benefits of delaying the onset of supplementation, shortening periods of supplementation, and escalating selenium supplementation beyond 100 µg/day. Supplementation with 200 µg selenium/day (as selenite or seleno-l-methionine) substantially improved the mitigation of radiation nephropathy by lowering BUN levels at 4 months after TBI from 115 to as low as 34 mg/dl and by proportionally lowering the incidence of histopathological abnormalities. Shortening the period of supplementation to 3 or 2 months did not compromise efficacy. Delaying the onset of supplementation for 1 week reduced but did not abrogate the mitigation of radiation nephropathy. Supplementation with 300 µg/day mitigated radiation nephropathy less effectively than 200 µg and was poorly tolerated. Rats that had been given 10 Gy of TBI were less tolerant of high-dose selenium than nonirradiated rats. This reduced tolerance of high-dose selenium would need to be taken into consideration when selenium is used for the mitigation of radiation injury in victims of nuclear accidents or acts of radiological terrorism. The high dose requirements, the pronounced threshold effect, and the superior performance of selenite suggest that the mitigation of radiation nephropathy involves mechanisms that go beyond the induction of selenoproteins.

An outbreak of granulomatous peritonitis caused by injectable selenium in a flock of Merino sheep

During meat inspection, unusual pigmented lesions were found in the abdomens of 411 sheep from a flock raised in the Northern Tablelands of New South Wales. In each affected sheep there were multiple discrete, soft, yellow homogeneous plaques beneath the parietal peritoneum and extending into marginating facial planes of the diaphragm and body wall. Microscopically, the lesions consisted of focal granulomatous peritonitis with intracellular acicular refractile golden-brown crystals. Energy dispersive X-ray spectroscopy revealed intralesional barium and selenium, two components of an injectable selenium compound administered to the sheep 6-8 months prior, which contains the yellow pigment, iron oxide. The mechanism of subperitoneal deposition of the compound could not be confirmed, but is presumed to have involved intraperitoneal injection of barium selenate. Meat inspectors and diagnosticians should consider barium selenate injection-site granulomas as a possible explanation for yellow pigmented lesions, especially in livestock from selenium-deficient areas. Animal care providers should be aware that incorrect administration of barium selenate can result in losses from condemnation or downgrading of meat product.

Lesions of thymus and decreased percentages of the peripheral blood T-cell subsets in chickens fed on diets excess in selenium

Selenium is an essential trace element possessing immune-stimulatory properties. The purpose of this 42-day study was to investigate the effects of excess dietary selenium on cellular immune function by determining morphological changes of thymus and peripheral blood T-cell subset. Three hundred 1-day-old avian broilers were fed on a basic diet (0.2 mg/kg selenium) or the same diet amended to contain 1, 5, 10, 15 mg/kg selenium supplied as sodium selenite ( n = 60/group). Pathological lesions were progressed with the dietary Se level increased. Grossly, the volume of thymus was decreased. Histopathologically, lymphopenia and congestion were observed. Ultrastructurally, mitochondria injury was observed. In comparison with that of control group, 5, 10 and 15 mg/kg dietary Se decreased the percentage of CD3+, CD3+CD4+ and CD3+CD8+ T cells of the peripheral blood, as measured by flow cytometry. The results showed that excess selenium (more than 5 mg/kg) intake could cause lesions of thymus and decrease of T-cell subsets. The cellular immune function was finally impaired in broilers.

The decrease of relative weight, lesions, and apoptosis of bursa of fabricius induced by excess dietary selenium in chickens

Selenium is an essential trace element possessing immune-stimulatory properties. The purpose of this 42-day study was to investigate the effects of excess dietary sodium selenite on immune function by determining morphological changes and apoptosis of bursa of Fabricius. Three hundred 1-day-old Avian broilers were fed on a basic diet (0.2 ppm selenium) or the same diet amended to contain 1, 5, 10, and 15 ppm selenium supplied as sodium selenite (n = 60/group). Relative weight of bursa was significantly decreased in the 1, 5, 10, and 15 ppm groups at 28 days of age, when compared with that of 0.2 ppm group. Pathological lesions were progressed with the dietary Se level increased. The gross lesions of bursa involved obvious atrophy with decreased volume and pale color. Histopathologically, decreased number of lymphocytes and loosely packed lymphocytes appeared in the medulla and cortex in the follicles. Ultrastructurally, mitochondria injury and increased apoptotic cells with condensed nuclei were observed. In comparison to that of control group, excess Se (5, 10, and 15 ppm) intake increased the percentage of Annexin V positive cells, as measured by flow cytometry. Terminal deoxynucleotidyl transferase 2'-deoxyuridine 5'-triphosphate nick end-labeling assay showed that there were increased frequencies of apoptotic cells in 10 and 15 ppm selenium groups. These data suggest that Se supplementation with sodium selenite should be carefully evaluated as excess selenium (more than 5 ppm) intake could cause profound immunologic inhibition.

Patogênese das lesões associadas à intoxicação por Ramaria flavo-brunnescens em bovinos

O estudo da patogênese da intoxicação pelo cogumelo Ramaria flavo-brunnescens em bovinos foi realizado através da avaliação retrospectiva de tecidos selecionados de nove casos espontâneos e quatro casos experimentais. Para a investigação da patogênese das lesões observadas na língua, esôfago, casco e cauda, foram avaliadas as alterações histopatológicas e aspectos histoquímicos e histoquímico-ultra-estruturais das lesões. As técnicas histoquímicas utilizadas foram o Tricrômico de Masson e a oxidação seletiva da ceratina (OSC). O estudo histoquímico-ultra-estrutural foi realizado através da técnica de Swift sob microscopia eletrônica de transmissão. Os pelos da vassoura da cauda foram examinados sob microscopia de luz polarizada. Todas as alterações observadas nas estruturas ceratinizadas estudadas, mas especialmente nas que sofrem ceratinização dura, revelaram defeitos na ceratinização. Aliando ao estudo morfológico os resultados obtidos através da técnica da OSC e da microscopia eletrônica/técnica de Swift pode-se associar os defeitos na ceratinização a uma redução na quantidade de aminoácidos sulfurados (cistina), principalmente nas estruturas que sofrem ceratinização dura, sendo este provavelmente o principal mecanismo patogenético na intoxicação por R. flavo brunnescens em bovinos.

Selenium in camel--a review

Requirements for trace minerals in camels, particularly selenium, are not well-known. Selenium supplementation using a pharmaceutical form or commercial mineral mixture is common practice in camels to address the cardiomyopathy often attributed to selenium deficiency. This supplementation is often empirical and based on estimated needs for cattle. Nowadays the use of selenium in animal foodstuffs is commonplace and further investigation of its metabolism (ingestion, dynamic of storage-destocking, excretion) in camels is warranted. The present review aimed to synthesize all the experimental research (comparative selenium status in cow and camel, response to different levels of supplementation at different physiological stages, excretion maternal transfer, experimental toxicosis) and field observations (deficiency, supplementation practices) undertaken in camels. The results underline the particularity of the unique metabolic profile of the camel and lead to practical recommendations for supplementation in camels, highlighting its relative sensitivity to excess Se intake at lower levels than in cattle. The maximal tolerable dose is 8 mg and the recommended doses range from 2 to 4 mg.

Strong poison revisited

Selenium in the form of selenocysteine plays an essential role in a number of proteins, but its role in non-enzymatic biochemistry is also important. In this short review we discuss the interactions between inorganic selenium, arsenic and mercury under physiological conditions, especially in the presence of glutathione. This chemistry is obviously important in making the arsenic and mercury unavailable for more toxic interactions, but in the process it suggests that a side-effect of chronic arsenic and/or mercury exposure is likely to be functional selenium deficiency.

Comparative toxicosis of sodium selenite and selenomethionine in lambs

Excess consumption of selenium (Se) accumulator plants can result in selenium intoxication. The objective of the study reported here was to compare the acute toxicosis caused by organic selenium (selenomethionine) found in plants with that caused by the supplemental, inorganic form of selenium (sodium selenite). Lambs were orally administered a single dose of selenium as either sodium selenite or selenomethionine and were monitored for 7 days, after which they were euthanized and necropsied. Twelve randomly assigned treatment groups consisted of animals given 0, 1, 2, 3, or 4 mg of Se/kg of body weight as sodium selenite, or 0, 1, 2, 3, 4, 6, or 8 mg of Se/kg as selenomethionine. Sodium selenite at dosages of 2, 3, and 4 mg/kg, as well as selenomethionine at dosages of 4, 6, and 8 mg/kg resulted in tachypnea and/or respiratory distress following minimal exercise. Severity and time to recovery varied, and were dose dependent. Major histopathologic findings in animals of the high-dose groups included multifocal myocardial necrosis and pulmonary alveolar vasculitis with pulmonary edema and hemorrhage. Analysis of liver, kidney cortex, heart, blood, and serum revealed linear, dose-dependent increases in selenium concentration. However, tissue selenium concentration in selenomethionine-treated lambs were significantly greater than that in lambs treated with equivalent doses of sodium selenite. To estimate the oxidative effects of these selenium compounds in vivo, liver vitamin E concentration also was measured. Sodium selenite, but not selenomethionine administration resulted in decreased liver vitamin E concentration. Results of this study indicate that the chemical form of the ingested Se must be known to adequately interpret tissue, blood, and serum Se concentrations.

Enfermidades associadas à intoxicação por selênio em animais

Por meio de revisão da literatura pertinente foram coligidos e são apresentados os principais dados relativos à intoxicação por selênio em animais domésticos. Foram abordados e discutidos os aspectos epidemiológicos, clínicos, anátomo e histopatológicos e patogenéticos atribuídos a Alkali Disease, Blind Staggers, intoxicação aguda e poliomielomalácia simétrica focal dos suínos. O trabalho tem como objetivo esclarecer pontos obscuros relativos à intoxicação por selênio, bem como alertar para os riscos que a suplementação com esse elemento pode representar.

Intoxicação por Ramaria flavo-brunnescens (Clavariaceae) em bovinos

Dois surtos de intoxicação pelo cogumelo Ramaria flavo-brunnescens são relatados em bovinos de duas fazendas localizadas nos municípios de Santa Maria e São Gabriel, no Rio Grande do Sul, no período de abril-maio de 2005. De um total de 180 bovinos de sobreano que tiveram acesso a bosques de eucaliptos, 19 adoeceram e 10 morreram. A evolução clínica foi de 8-15 dias e os sinais clínicos incluíam depressão, perda de peso, desidratação, salivação excessiva, afrouxamento e perda dos pêlos longos da cauda, alisamento da superfície dorsal da língua com ocasional ulceração, afrouxamento do estojo córneo dos chifres, fezes em forma de cíbalos e recobertas por película de muco, hipópion, hifema e opacidade da córnea. Dois novilhos tinham leucocitose devido a leve desvio regenerativo à esquerda. Os achados de necropsia confirmaram as observações clínicas e adicionalmente incluíam esofagite fibrinonecrótica, principalmente no terço distal do esôfago. Alterações histopatológicas na pele da cauda incluíam hiperqueratose ortoqueratótica, folículos pilosos com contornos irregulares, espessamento da camada de queratina tricolemal e formação ocasional de tampões de queratina; degeneração e necrose da bainha radicular externa também era observada. Nos cascos havia hemorragia, fibrina e infiltrado neutrofílico nas lâminas dérmicas, hiperplasia do topo das lâminas epidérmicas com queratinização irregular e retenção dos núcleos; várias lâminas epidérmicas estavam encurtadas e fundidas. Na mucosa da língua o epitélio de revestimento estava adelgaçado, com atrofia e perda das papilas filiformes, áreas multifocais de disqueratose e espongiose das células da camada basal. Em algumas porções havia perda do epitélio e a superfície da língua era formada por tecido de granulação e infiltrado inflamatório misto. A mucosa esofágica de seis novilhos apresentava vários graus de necrose epitelial e inflamação. A perda do epitélio de revestimento revelava uma área subjacente de tecido de granulação com marcado infiltrado inflamatório predominantemente neutrofílico e macrofágico. Em seis novilhos, o bulbo, na altura do óbex, apresentava áreas focais bilaterais e simétricas de malacia que afetava a substância branca e partes do núcleo dorsal do vago e do núcleo hipoglosso. São discutidos a epidemiologia, os sinais clínicos, a patologia e a patogênese da intoxicação por R. flavo-brunnescens em bovinos.

Selenite-induced apoptosis of osteoclasts mediated by the mitochondrial pathway

The possible effects of sodium selenite on mature osteoclasts were investigated. Incubation of osteoclast-like cells differentiated from RAW 264.7 cells with sodium selenite induced apoptosis as revealed by morphological changes, internucleosomal DNA fragmentation, and activation of caspase-3. Selenite also induced generation of the superoxide anion and reduced the number of free thiol groups in the osteoclast-like cells, suggestive of a shift to a more oxidizing intracellular environment. In addition, selenite induced protein aggregation by thiol cross-linking, loss of the mitochondrial membrane potential, and cytochrome c release in mitochondria isolated from the osteoclast-like cells. Finally, selenite-induced DNA fragmentation in osteoclasts was inhibited both by cyclosporin A, a blocker of the mitochondrial permeability transition pore, and by DEVD-CHO, a cell-permeable inhibitor of caspase-3. These results thus suggest that selenite induces apoptosis mediated by the mitochondrial pathway in mature osteoclasts.

Myositis, lameness, and recumbency after use of water-in-oil adjuvanted vaccines in near-term beef cattle

A producer administered 2 US Department of Agriculture-licensed adjuvanted veterinary vaccines (inactivated bovine rotavirus-coronavirus vaccine; Clostridium perfringens type C-Escherichia coli bacterin-toxoid) into muscles of the left and right hips of 469 pregnant beef cows. Within 24 hours, 5 cattle were recumbent, and another 2 had non-weight bearing pelvic limb lameness (1.5% affected; 7/469). During the next 10 days, 50% of the herd developed firm swellings up to 24 cm in vaccination sites in muscles of the hip. Histological samples revealed granulomatous myositis with intralesional oil. Lesions resolved slowly during the next 6 months. Six cattle were injected experimentally with the vaccines. None became lame, but all developed foreign body granulomatous myositis similar to those in the affected herd. The maximum diameter of experimentally induced lesions in muscle at necropsy 60 days after injection with the recommended dose of the bacterin-toxoid vaccines was 12 cm. Histological examination revealed pyogranulomatous myositis, fibrosis, and myonecrosis. The inactivated viral vaccine induced milder granulomatous myositis with intralesional lipid and scant fibrosis. Acute transient lameness on the ranch was attributed to use of 2 irritating biological vaccines in the hip muscles of cows that were close to parturition.

Use of a topical disinfectant as part of a hoof care programme for horses with diseases of the hoof capsule

Twenty-three horses with persistent hoof horn defects were treated topically with a hoof disinfectant as part of a hoof care programme for a year. The active ingredients of the disinfectant were a poloaximer-iodine complex, ethylenediamine dihydriodide, isopropyl alcohol and propylene glycol. Hoof trimmings were taken at the start of the study and every six weeks, and examined by scanning and transmission electron microscopy. At the beginning of the study all the horn samples contained large numbers of bacteria, and samples from eight of the horses also had fungal hyphae intermingled with the bacteria. After the application of the hoof disinfectant and adjustments to their diet, there were rapid improvements in the gross appearance of the feet of all the horses; some of them improved within two to three weeks and by 12 weeks the horn quality of all the horses had greatly improved.

Histochemical and ultrahistochemical localization of heavy metals in calf organs

Cadmium, zinc, selenium, and copper were administered, singly or in combination, orally or subcutaneously. Experiment I included 32 calves of both sexes; six received Cd (two groups), Zn, Cd, and Zn, and Cd and Se (two groups) and one group was a control. In Experiment II (21 bulls), three were given Cd, Cd, and Cu, and Cd and Zn, respectively, and one group was a control. For light microscopy, in Experiment I the highest amounts of silver granules were present in the samples of liver, small intestine, and vesicular gland of all the exposed groups; in Experiment II the most affected organs were liver, kidney, and small intestine. For electron microscopy, in Experiment I, after administration of Cd and Zn, the highest amounts of granules were seen in the cytoplasm of hepatocytes and cells of the proximal and distal renal tubules and the lowest amounts were found in glandular cells of the pancreas. Administration of Cd and Se resulted in the presence of large numbers of granules in the nuclei and nucleoli of spermatogonies. In Experiment II, ingestion of Cd and Zn in feed led to the appearance of highest amounts of granules in the nucleoli, nuclei, and cytoplasm of cells in testes, kidneys, and pancreas. Following Cd intake, the highest accumulation of granules was observed in the nucleoli of hepatocytes and cells of the proximal and distal renal tubules. Combined Cd and Cu produced the highest number of granules in cells of the proximal and distal renal tubules and in the nucleoli and nuclei of germinal epithelium.

Aspectos clínico-patológicos da intoxicação experimental por selenito de sódio em eqüinos

Dadas as controvérsias sobre a intoxicação por selênio, foram realizados nove experimentos com a administração de selenito de sódio, por via intramuscular, em eqüinos, com o intuito de estudar e melhor fundamentar os aspectos clínico-patológicos e toxicológicos sobre esse tema. Conseguiram-se produzir quadros com evoluções superaguda, aguda, subaguda e crônica; alguns sinais clínicos de origem nervosa observados nos quadros agudos foram similares aos descritos para "blind staggers"; a despeito disto, o carácter conflitante e duvidoso das descrições sobre essa pretensa entidade historicamente descrita, não permite uma comparação mais exata. O quadro crônico, por outro lado, configurou claramente a primeira reprodução de "alkali disease", por via parenteral, em eqüinos. Estabeleceu-se 1,49 mg/kg de selenito de sódio como a dose única letal para essa espécie. Descrevem-se diversos achados clínico-patológicos relativos aos sistemas cardiovascular e nervoso, antes não mencionados na literatura relativa aos eqüinos intoxicados por selênio. Entre eles, destacam-se, clinicamente, sopro e arritmia cardíacos, desdobramento de bulhas e convulsão. À necropsia, um animal apresentou nítido achatamento das circunvoluções cerebrais e, em relação à histopatologia, lise e necrose de neurônios do córtex, edema de astrócitos, bem como ativação endotelial e gliose. Em relação à patogênese, postula-se que as alterações degenerativo-necróticas observadas no sistema nervoso central, devam-se ao edema, por sua vez conseqüente ao aumento da permeabilidade vascular, determinada pelo selenito de sódio.

Selenosis

Despite more than six decades of research, some aspects of the natural history of selenosis remain confused in modern texts. The primary targets of acute Se toxicity in food animal species are the cardiovascular, gastrointestinal, and possibly hematopoietic systems. Swine may develop neurologic lesions; however, the signs of poliomyelomalacia are quite distinct from those described as "blind staggers" by early workers. The most characteristic signs of chronic selenosis are hair and hoof loss; however, other, less specific, damage to the immune system and reproduction are economically more important. Given the numerous interactions of chronic Se with other dietary factors, it is very important to examine the whole environment when dealing with a potential selenosis case.

The effect of subclinical selenium toxicosis on pregnant beef cattle

A field investigation conducted by the South Dakota Animal Disease Research and Diagnostic Laboratory suggested that subclinical selenium toxicosis in pregnant cows may have contributed to an outbreak of aborted/stillborn calves in a high-selenium region of South Dakota. This study was undertaken to evaluate the relationship between abortion and subclinical selenium toxicosis in the dam and to assess the effects of subclinical selenium toxicosis on the bovine immune system. Fifteen pregnant cows were fed diets containing 0.25 (control), 6.0, and 12.0 ppm selenium beginning at 80-110 days gestation. Although selenium toxicosis has been reported to cause abortion, this study failed to reproduce abortions. A single cow in the 12-ppm selenium treatment group gave birth to a weak calf, which subsequently died. This calf had myocardial lesions consistent with those described for selenium toxicosis and had hepatic selenium levels of 9.68 ppm (wet weight). Elevated dietary selenium resulted in the depression of several leukocyte function parameters in pregnant cows. A statistically significant depression in forced antibody response was identified in both selenium-supplemented groups. A significantly diminished mitogenic response to concanavalin A and pokeweed mitogen was also observed in the 12-ppm selenium group. Although a similar pattern of depression was also observed with phytohemagglutinin, differences were not significant. These findings indicate that even in the absence of clinical alkali disease, elevated selenium levels may adversely affect both pregnancy outcome and the bovine immune system.

Experimentally induced selenosis of adult mallard ducks: clinical signs, lesions, and toxicology

Selenosis is thought to be a significant problem among waterfowl populations in selenium-contaminated wetlands in the western United States. Chemical analysis of avian tissues is currently the principal basis for diagnosis. The purpose of these two 150-day studies was to establish whether morphological criteria for selenosis could be developed to supplement chemical analysis. Forty-eight flightling male mallard ducks were fed either a proprietary waterfowl ration (< 1 ppm selenium) or the same ration amended to contain 10, 25, and 60 ppm selenium supplied as seleno-L-methionine (n = 12/group). In a separate study, 12 birds fed twice daily were offered either a proprietary ration or a selenium-supplemented ration (120 microg/g) for one of two daily feedings. Selenium in whole blood increased from baseline concentrations (< 0.4 microg/ml) to means of 4.5, 8.9, and 16.0 microg/ml in the 10-, 25-, and 60-ppm groups, respectively. All birds in the 60-ppm-dose group rapidly lost weight and were killed (11/12) or died (1/12) between 22 and 50 days of dietary exposure. In addition to emaciation, six of 12 birds (50%) fed the 60-microg/g diet developed mild to moderate generalized hepatopathy with single-cell necrosis, karyomegaly of hepatocytes, hyperplastic bile duct epithelium, and/or iron accumulation in Kupffer cells. The principal lesions in birds exposed to other dietary concentrations of selenium involved integumentary structures containing hard keratin. Gross lesions developed after 76 days of dietary exposure and consisted of bilaterally symmetrical alopecia of the scalp and dorsal cervical midline, broken or lost digital nails, and necrosis of the tip of the beak (maxillary nail). One or more of these three lesions were present in 0/12 birds (0%) fed 10 ppm selenium, 5/12 birds (42%) fed 25 ppm selenium, and 4/9 (44%) birds fed a split-feed diet containing 120 ppm selenium. Controls were unaffected. Histologic lesions in digital and maxillary nails consisted of single-cell to full-thickness necrosis of keratinocytes and multifocal parakeratosis in stratum corneum. Histologic lesions in alopecic skin (necrosis of the epidermal collar, inflammation of the feather pulp, and follicular keratosis) were mild. Some birds with alopecia had no detectable lesions in feather follicles from affected areas of skin. The highest tissue concentrations of selenium were in liver, kidney, and feathers, respectively. Mean hepatic tissue concentrations were 14.5 microg/g (10 ppm group), 29.6 microg/g (25 ppm group), 60.6 microg/g (60 ppm group), 13.0 microg/g (120 ppm split-feed group), and 2.0 microg/g (controls). Integumentary and hepatic lesions may be of value in corroborating a diagnosis of selenosis based on chemical analysis of tissues from naturally intoxicated waterfowl. Some birds with fatal selenosis may have no morphologic lesions other than emaciation.

Acute hydrogen selenide gas poisoning admissions in one of the hospitals in Delhi, India: case report

Acute gas poisoning is one of the most important medicosocial problems in the developing countries. An outbreak of acute inhalation exposure to hydrogen selenide occurred in Delhi, India. This report includes our findings on epidemiological, clinical and biochemical investigations in 31 cases hospitalized immediately after the gas poisoning.