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Iodine in animal nutrition with implication to the human

Friedrich Schöne

Abstract The iodine consumption of the German population is not sufficient yet. Besides iodine salt milk and milk products contribute to iodine supply at a great extent. In general also the eggs may be enriched by higher feed iodine addition. However, meat is poor in iodine and in dose response experiments with fattening pigs and bulls also a high feed iodine supplementation could not increase the meat iodine content in a nutritionally relevant manner. This overview focuses at recent trials on dairy cows with investigations of the iodine content in milk in relation to the iodine of the cow feed. Regarding rapeseed feeds as potential home-grown high-protein alternatives to soybean meal an influence of the rapeseed iodine antagonists, the glucosinolates (GSL), was to test mainly on the content of iodine in milk. Iodine was quantified by means of mass spectrometry with inductively coupled plasma (ICP-MS), in the feedingstuffs and the lyophhilized milk after alkaline extraction. As a rule the analyses confirmed iodine supplementation levels in the investigated mineral vitamin premixes. In the non-iodine-supplemented feedingstuffs a very low iodine concentration was detected: from < 0.07 mg/kg dry matter, DM (limit of quantification) in grain to 0.3 mg iodine/kg DM in ensiled fodder. Ash and iodine of the grass silages were positively correlated indicating an iodine input by soil contamination during the harvest and preparation of fodder in the silo. Neglecting the native iodine and its probably low availability in the feedingstuffs the German Society of Nutritional Physiology recommends a minimum supplementation of 0.5 – 0.6 mg iodine/kg feed DM for dairy cows (GfE 2001). In recent German cow experiments with diets consisting of silages, grain and soybean meal, iodine in a concentration range of 0.8 – 1.4 mg /kg diet DM created milk iodine concentrations in a magnitude of >100 to 350 µg /litre. Inclusion of rapeseed feeds diminished the milk iodine concentration in a range from one third to two third. Regarding concentrations of less than 100 µg iodine/ litre milk caused by rapeseed feeds the presence of GSL requires an increase of the iodine supplementation at 2 - 3 mg/kg diet DM, i.e. the 4 to 6fold of the recommended supplementation of dairy cow diets free of iodine antagonists. As a resumee human eating habits are discussed using milk(products) differing in iodine over a broad concentration range which may cause an insufficient, optimal or a too high intake of iodine. The derived recommendations for human iodine supply interact with the recommendations of animal nutritionists making more transparent the flow of the trace element in the food chain.