Effects of Dietary Iron on Performance and Mineral Utilization in Lambs Fed a Forage-Based Diet

Twenty-four lambs, averaging 29 kg, were used to determine the effect of supplemental dietary Fe on performance and Cu, P, Zn and Mn utilization. Treatments consisted of supplemental Fe at 0, 300, 600 or 1,200 mg/kg diet as ferrous carbonate. The basal diet contained 154 mg Fe/kg diet and consisted of 90% Coastal bermudagrass pellets, 9.45% ground corn, .5% sodium chloride and .05% vitamin mix. Lambs were slaughtered after having ad libitum access to diets for 98 to 121 d. Dietary Fe did not affect lamb gain or feed intake. Supplemental Fe increased Fe concentrations in liver (P < .01), spleen (P < .01) and bone (P < .10), but not in kidney and muscle. Serum Fe concentrations and percentage transferrin saturation in serum were increased (P < .01) by supplemental Fe at 28 and 84 d, but not at the termination of the study. Plasma Cu was decreased (P < .01) at 56 d, whereas serum ceruloplasmin activity was reduced (P < .01) at 28 d in lambs fed 1,200 mg Fe/kg diet compared with lambs fed 600 mg Fe/kg diet. Lower levels of Fe (300 and 600) reduced (P < .01) ceruloplasmin by 56 d and plasma Cu by 84 d compared with controls. Liver Cu also was decreased (P < .05) by supplemental Fe. Plasma P was decreased slightly (P < .10) by 28 d and significantly (P < .01) at the other sampling dates by supplemental Fe. However, the decrease in plasma P due to Fe was relatively small, and bone P was not affected by treatment. Zinc status was not affected by dietary Fe based on plasma Zn, serum alkaline phosphatase activity and tissue Zn concentrations. Tissue concentrations of Mn also were not affected by treatment. Results indicate that Fe concentrations frequently present in forages will decrease Cu stores and Cu transport and storage proteins of lambs fed forage-based diets.