Changes

==Toxicity==

==Toxicity==

===Dog:===   

===Dog:===   

Selenium is probably the only nutrient that was studied for its toxic effects many years before its essentiality was discovered. A study in 1943<ref>Rhian, M, Moxon, AA (1943). “Chronic selenium poisoning in dogs and its prevention by arsenic”. J. Pharm. Exp. Therap. 78:249-264.</ref> showed that dietary selenium contents of 10 mg/kg DM as sodium selenite or 7.2 mg/kg DM as organic selenium were toxic to dogs as indicated by impaired growth and low food intake. More recent investigations showed that when dogs were fed a dietary selenium content of 5 mg/kg DM for 24 weeks resulted in both a reduction in food intake and impaired hair growth<ref>Wedekind, KJ, Kirk, CA, Yu, S, Nachreiner, RF (2002). “Defining the safe lower and upper limits for selenium (Se) in adult dogs”. Fed. Proc. 16:A992-A993.</ref><ref>Yu, S, Wedekind, KJ, Kirk, CA, Nachreiner, RF (2006). “Primary hair growth in dogs depends on dietary selenium concentrations”. J. Anim. Physiol. Anim. Nutr. 90:146-151.</ref>.

Selenium is probably the only nutrient that was studied for its toxic effects many years before its [[Nutrition Glossary#Essential Nutrients|essentiality]] was discovered. A study in 1943<ref>Rhian, M, Moxon, AA (1943). “Chronic selenium poisoning in dogs and its prevention by arsenic”. J. Pharm. Exp. Therap. 78:249-264.</ref> showed that dietary selenium contents of 10 mg/kg DM as sodium selenite or 7.2 mg/kg DM as organic selenium were toxic to dogs as indicated by impaired growth and low food intake. More recent investigations showed that when dogs were fed a dietary selenium content of 5 mg/kg DM for 24 weeks resulted in both a reduction in food intake and impaired [[Hair - Anatomy & Physiology|hair]] growth<ref>Wedekind, KJ, Kirk, CA, Yu, S, Nachreiner, RF (2002). “Defining the safe lower and upper limits for selenium (Se) in adult dogs”. Fed. Proc. 16:A992-A993.</ref><ref>Yu, S, Wedekind, KJ, Kirk, CA, Nachreiner, RF (2006). “Primary hair growth in dogs depends on dietary selenium concentrations”. J. Anim. Physiol. Anim. Nutr. 90:146-151.</ref>.

===Cat:===   

===Cat:===   

Cats seem to be more resistant than dogs to the toxic effects of selenium. Adult cats were fed up to 10 mg selenium/kg diet DM in an organic form (selenomethionine) for 26 weeks with no signs of toxicity<ref>Wedekind, KJ, Kirk, CA, Yu, S, Nachreiner, RF (2003). “Defining the safe lower and upper limits for selenium in adult cats”. J. Anim. Sci. 81(suppl.):90 (abstr.).</ref>. The difference in selenium tolerance between the two species can be explained by the fact that cats are more efficient at excreting excess selenium in the urine and store less selenium in the liver<ref name="Todd">Todd, SE, Thomas, DG, Bosch, G, Hendriks, WH (2012). “Selenium status in adult cats and dogs fed high levels of dietary inorganic and organic selenium”. J. Anim. Sci. 90:2549-2555.</ref>.

Cats seem to be more resistant than dogs to the toxic effects of selenium. Adult cats were fed up to 10 mg selenium/kg diet DM in an organic form (selenomethionine) for 26 weeks with no signs of toxicity<ref>Wedekind, KJ, Kirk, CA, Yu, S, Nachreiner, RF (2003). “Defining the safe lower and upper limits for selenium in adult cats”. J. Anim. Sci. 81(suppl.):90 (abstr.).</ref>. The difference in selenium tolerance between the two species can be explained by the fact that cats are more efficient at excreting excess selenium in the urine and store less selenium in the [[Liver - Anatomy & Physiology|liver]]<ref name="Todd">Todd, SE, Thomas, DG, Bosch, G, Hendriks, WH (2012). “Selenium status in adult cats and dogs fed high levels of dietary inorganic and organic selenium”. J. Anim. Sci. 90:2549-2555.</ref>.

===Dietary Sources===

===Dietary Sources===

Selenium is found in a wide variety of plant and animal sources but usually at low concentrations. Meats, fish and bread are reported to supply good amounts of bioavailable selenium. Some studies suggest that plant sources are more bioavailable than animal sources. In commercial pet foods selenium bioavailabilities of 30% and 53% for canned and dry products, respectively have been reported<ref>Wedekind, KJ, Beyer, R, Combs Jr, GF (1998). “Is selenium addition necessary in petfoods?”. FASEB J. 12:A823.</ref>. To ensure nutritional adequacy pet foods can be supplemented with inorganic selenium compounds such as sodium selenate or selenite or an organic source like selenomethionine. The bioavailabilities of these selenium compounds appear to be similar: a study comparing high intakes of selenium in cats and dogs fed selenium in either inorganic or organic forms found no major differences in results for the two sources<ref name="Todd"/>.  

Selenium is found in a wide variety of plant and animal sources but usually at low concentrations. Meats, fish and bread are reported to supply good amounts of [[Nutrition Glossary#Bioavailability|bioavailable]] selenium. Some studies suggest that plant sources are more bioavailable than animal sources. In commercial pet foods, selenium bioavailabilities of 30% and 53% for canned and dry products, respectively have been reported<ref>Wedekind, KJ, Beyer, R, Combs Jr, GF (1998). “Is selenium addition necessary in petfoods?”. FASEB J. 12:A823.</ref>. To ensure nutritional adequacy pet foods can be supplemented with inorganic selenium compounds such as sodium selenate or selenite or an organic source like selenomethionine. The bioavailabilities of these selenium compounds appear to be similar: a study comparing high intakes of selenium in cats and dogs fed selenium in either inorganic or organic forms found no major differences in results for the two sources<ref name="Todd"/>.

==References==

==References==