Influence of Dietary Iron and Phosphorus on Performance, Tissue Mineral Composition and Mineral Absorption in Steers

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Abstract
Twenty-four steer calves of beef breeding were group fed for 77 days in four replicated lots of three steers each to study the effect of dietary iron and phosphorus on feedlot performance and mineral composition of selected tissues. The treatments consisted of two diets containing 100 ppm iron and either 0.23 or 0.46% phosphorus and two diets containing 1,000 ppm iron in combination with two phosphorus levels. Average daily gain was depressed (P<.05) in the steers fed the high-iron diets and was not affected significantly by increasing dietary phosphorus at either iron level. Plasma phosphorus was decreased (P<.01) by the higher level of dietary iron and increased by the higher level of dietary phosphorus after 45 days on trial but not after 77 days. Iron concentrations were increased in the liver, spleen, heart, muscle (P<.01) and kidney (P<.05) when 1,000 ppm dietary iron was fed. The high-iron diets also produced lower copper levels in the liver (P<.01). Zinc levels were reduced (P<.05) in the liver and increased (P<.05) in the spleen of steers fed the high-iron diets. Liver calcium was reduced (P<.05) as were kidney and heart manganese levels (P<.01) by high dietary iron. Kidney and heart magnesium levels, however, were increased by these diets. The high phosphorus diets resulted in decreased iron levels in the liver and kidney (P<.01) and increased liver magnesium (P<.05). A latin-square design study utilizing four steers was conducted to determine the apparent absorption of minerals from the diets described above. Absorption of copper and magnesium was depressed (P<.01) by feeding the high-iron diets. The high-phosphorus diets resulted in decreased (P<.01) absorption of calcium and magnesium. Copyright © 1971. American Society of Animal Science . Copyright 1971 by American Society of Animal Science.

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