Comparative effects of high dietary levels of organic and inorganic selenium on selenium toxicity of growing-finishing pigs

Association of maximum voluntary dietary intake of freeze-dried garlic with Heinz body anemia in horses

OBJECTIVE

To characterize hematologic and clinical consequences of chronic dietary consumption of freeze-dried garlic at maximum voluntary intake in horses.

ANIMALS

4 healthy sex- and age-matched horses.

PROCEDURE

An initial garlic dose (0.05 g/kg, twice daily) was fed to 2 horses in a molasses carrier as part of their normal ration and was gradually increased to maximum voluntary intake (0.25 g/kg, twice daily) over 41 days. Dietary supplementation then continued for a total of 71 days. Two control horses were fed molasses with no garlic with their ration. Blood samples were collected weekly and analyzed for hematologic and biochemical changes, including the presence of Heinz bodies. Recovery of affected blood values was followed for 5 weeks after termination of dietary supplementation with garlic.

RESULTS

At a daily dose of > 0.2 g/kg, horses fed garlic developed hematologic and biochemical indications of Heinz body anemia, as characterized by increases in Heinz body score (HBS), mean corpuscular volume (MCV), mean corpuscular hemoglobin, platelet count, and serum unconjugated and total bilirubin concentrations and decreases in RBC count, blood hemoglobin concentration, mean corpuscular hemoglobin concentration, and serum haptoglobin concentration. Recovery from anemia was largely complete within 5 weeks after termination of dietary supplementation with garlic. Heinz body score and MCV remained high at the end of the 5-week recovery period.

CONCLUSIONS AND CLINICAL RELEVANCE

Horses will voluntarily consume sufficient quantities of garlic to cause Heinz body anemia. The potential for garlic toxicosis exists when horses are chronically fed garlic. Further study is required to determine the safe dietary dose of garlic in horses.

Effect of supranutritional and organically bound selenium on performance, carcass characteristics, and selenium distribution in finishing beef steers

Dietary selenium influences the Se content in edible muscle of beef cattle. Limited data are available to describe the effects that feeds naturally high in Se have on production, carcass characteristics, and Se distribution in terminal tissues. Therefore, 43 crossbred steers (BW = 351 +/- 24 kg) were stratified by BW and assigned to one of four dietary treatments: Se adequate (CON; n = 12), Se provided as high-Se wheat (WHT; n = 9), high-Se hay (HAY; n = 11), or sodium selenate (SEO; n = 11). Daily selenium intake for WHT, HAY, and SEO diets was 65 microg/kg BW, whereas it was 9.5 microg/kg BW for CON. Diets were similar in ingredient composition (25% wheat, 39% corn, 25% grass hay, 5% desugared molasses, and 6% wheat middling-based supplement; DM basis), isonitrogenous and isocaloric (14.0% CP, 2.12 Mcal NEm/kg DM and 1.26 Mcal NEg/ kg DM), and offered once daily (1500) individually to steers in a Calan gate system for 126 d. At the end of the trial, steers were slaughtered; carcass data were recorded; and samples of the liver, kidney, spleen, semitendinosus, and hair were collected for Se analysis. Intake of DM, G:F, and ADG did not differ (P > 0.13). No differences (P > 0.12) were noted for hot carcass weight, organ weights, longissimus muscle area, back-fat thickness, marbling scores, or quality and yield grade. Kidney, pelvic, and heart fat tended to be higher (P = 0.06) in CON and WHT compared with SEO and HAY steers (2.9, 2.4, 2.5, 2.9 +/- 0.2% for CON, SEO, HAY, and WHT, respectively). Selenium concentrations in all tissues collected differed (P < 0.003) due to treatment. Distribution of Se to the kidney, spleen, and hair were similar with CON < SEO < HAY < WHT (8.40, 10.05, 10.86, 12.89 +/- 0.26 ppm for kidney; 2.00, 2.60, 3.82, 5.16 +/- 0.09 ppm for spleen; 1.80, 4.00, 5.93, 10.54 +/- 0.56 ppm for hair; P < 0.01). The distribution of Se in liver and muscle (DM basis) differed from that in other tissues, with CON < HAY < SEO = WHT (2.33, 6.56, 9.91, 10.79 +/- 0.80 ppm; P < 0.01) and CON = SEO < HAY < WHT (1.33, 1.55, 3.32, 4.41 +/- 0.18 ppm; P < 0.01), respectively. When providing dietary Se at supranutritional levels, source of Se did not affect production or carcass characteristics, but it altered the distribution and concentration of Se throughout the tissues of finishing beef steers.

The nutritional significance, metabolism and toxicology of selenomethionine

SeMet is a naturally occurring toxic amino acid but at the same time represents the major nutritional source of selenium for higher animals and humans. The ability of SeMet to be incorporated into the body proteins in place of Met furthermore provides a means of reversible Se storage in organs and tissues. This property is not shared by any other naturally occurring selenoamino acid and thus could be associated with a specific physiological function of SeMet. Since higher animals cannot synthesize SeMet, yet from it all needed forms of Se are produced, SeMet meets the criteria of an essential amino acid. Accordingly, SeMet, or enriched food sources thereof, are appropriate forms of Se for human nutritional Se supplementation. However, while SeMet or Se yeast are already widely used in over-the-counter nutritional supplements, infant formulas and parenteral feeding mixtures still contain Se in the form of sodium selenate or sodium selenite, even though these are not the normal nutritional forms of Se. In animal nutrition, these inorganic selenium salts are increasingly replaced by food sources of SeMet such as Se yeast. Synthetic SeMet could also be employed as a feed additive, but its regulatory status is as yet undetermined. The optimal nutritional levels of SeMet for different animal species still need to be determined. The expectation is that lower additions to feedstock of equivalent levels of SeMet will suffice to achieve adequacy than currently approved maximum levels of Se in the form of inorganic Se salts.