Effect of Dietary Aluminum and Phosphorus on Performance, Phosphorus Utilization and Tissue Mineral Composition in Sheep2

An experiment was conducted to determine the effects of dietary Al and P on P utilization and tissue mineral composition in sheep. Twenty Florida native wether lambs, averaging 36.7 kg, were assigned to four groups in a 2 × 2 factorial arrangement of treatments, with two levels of dietary P as NaH2PO4 (.15 and .29%) and two levels of supplemental Al as A12C13•6H2O (0 and 2,000 ppm). Lambs were used in the same design in three experiments; a feeding trial, a P balance study, and a tissue mineral study. During the 56-d feeding trial, average daily gains by lambs in the four treatments (low P-low Al, high P-low Al, low P-high Al and high P-high Al) were 109, 116, −38 and 15 g, and average daily dry matter intakes were 1,280, 1,320, 780 and 1,080 g, respectively. Both dietary Al and P influenced (P<.05) these values. At the end of the feeding trial, plasma P was lower (P<.05) for sheep given high Al diets and higher (P<.01) for sheep given high P diets. Plasma Ca was decreased (P<.05) by high P and Mg was depressed (P<.01) by high Al. Three lambs in each group were injected iv with .2 mCi of 32for 10 consecutive d before the P balance study. True P absorption coefficients were 28.7, 32.8, −9.2 and 8.5%, and net P retention −48, −4, −404 and −325 mg/animal daily for the four treatment groups, respectively. Al depressed (P<.05) P absorption and retention. Metabolic fecal P averaged 483, 820, 206 and 460 mg/animal daily, respectively, and was influenced (P<.05) by P and Al in the diet. Apparent Ca absorption was reduced (P<.05) by dietary Al. Dry matter and organic matter digestibilities and apparent Mg absorptions were not affected by dietary P or Al. Liver Al levels increased (P<.01) with the high Al diet, and Al also tended to increase in kidney and longissimus muscle. Brain Al was not related to dietary Al. Fe (P<.05) in liver and kidney and Cu (P<.01) in kidney increased and Mg decreased (P<.01) as a result of high dietary Al. Zn in kidney (P<.01) and Mn in muscle (P<.05) decreased with high P diets. For all minerals studied, brain seemed to be the least affected by dietary mineral levels.