Feed & Additive Magazine Issue 47 December 2024

ISSUE FOCUS FEED & ADDITIVE MAGAZINE December 2024 29 diets (Figure 3). All diets remained within the minimum (0.220 mg/kg DM) and maximum (0.568 mg/ kg DM) levels of selenium for adult dogs. Of the vegetarian foods, 4 out of 6 diets barely exceeded the minimum requirements, where all lamb-based diets were above the 0.3 mg/kg DM. Sodium selenite was the most used source of supplemental selenium, only one diet was enriched with a selenized yeast. Within each brand, the vegetarian diet contained a (slightly) higher level of additional selenium, with only one exception. In line with earlier publications3, selenium derived from the raw materials is significantly lower in plantbased diets compared to the meat-based variants. In all diets, the amount of selenium from the raw materials was low (≤ 0.300 mg/kg DM). In two-third of the diets, the amount of selenium from raw materials did not exceed the minimum levels to fulfill in the requirements of dogs. Selenium supplementation of pet diets is therefore essential. However, what is a rational choice when we look at the different selenium sources that are commercially available? DIFFERENCE OF SELENIUM SOURCES IN THE METABOLISM Both plant-based and animal-based ingredients contain selenium, predominantly in the natural, organic form of L-selenomethionine. Supplemented selenium can be either inorganic (often sodium selenite) or organic (selenized yeast or L-selenomethionine). In the metabolism of the animal, there is a difference between L-selenomethionine and other forms of selenium (Figure 4). All selenium compounds are recognized for the supply of selenium, and all can be used for the synthesis of selenoproteins (selenoenzymes). It is the selenoenzymes that play a vital role in antioxidant defense, regulation of the thyroid function, and immune system support. Beside this general pathway to selenoenzymes, L-selenomeSe in the diet L-Selenomethionine Incorporation in animal proteins Seleno enzymes Excretion Other Se compounds . Selenocysteine (Se-Cys) . Other (organic) Se intermediates . Inorganic Se Via breath and urine x de novo Se-Cys H2Se Selenide . Glutathion peroxidase . Antioxidant role . Immunity . Se status, storage in tissue, Se reserve for later mobilization (protein turnover) . Se transfer to offspring via milk Se in the metabolism Figure 4. Dietary selenium sources in the metabolism Figure 3. Average selenium levels of 12 commercially available vegetarian and lamb-based dog diets, from 6 different brands. Total Se (analysed) Added Se Vegetarian Lamb-based Se from raw materials (mg Se/kg DM) a b 0,45 0,4 0,35 0,3 0,25 0,2 0,15 0,1 0,05 0 Selenium in vegetarian and lamb-based dog diets

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