Effects of iron supplementation on binding activity of iron regulatory proteins and the subsequent effect on growth performance and indices of hematological and mineral status of young pigs 1,2 M. J. Rincker*, S. L. Clarke†, R. S. Eisenstein†, J. E. Link*, and G. M. Hill* 3 *Department of Animal Science, Michigan State University, East Lansing 48824; and †Department of Nutritional Sciences, University of Wisconsin, Madison 53706 ABSTRACT: Two experiments were conducted to evaluate the effects of supplemental Fe on the binding activity of iron regulatory proteins (IRP) and the subse- quent effect on growth performance and indices of he- matological and mineral status of young pigs. In Exp. 1, male pigs (n = 10; 1.8 kg; age = 14 ± 1 h) were allotted by BW to two treatments (five pigs per treatment). Treatments administered by i.m. injection were as fol- lows: 1) 1 mL of sterile saline solution (Sal); and 2) 1 mL of 200 mg Fe as Fe-dextran (Fe). Pigs were bled (d 0 and 13) to determine hemoglobin (Hb), hematocrit (Hct), transferrin (Tf), and plasma Fe (PFe), and then killed (d 13) to determine spontaneous and 2-mercapto- ethanol (2-ME)-inducible IRP RNA binding activity in liver and liver and whole-body mineral concentrations. Contemporary pigs (n = 5; 2.2 kg; age = 14 ± 2 h) were killed at d 0 to establish baseline (BL1) measurements. In Exp. 2, pigs (six pigs per treatment; 6.5 kg; age = 19 ± 3 d) were fed a basal diet (Phase 1 = d 0 to 7; Phase 2 = d 7 to 21; Phase 3 = d 21 to 35) supplemented with 0 or 150 mg/kg of Fe as ferrous sulfate and killed at d 35 (18.3 kg; age = 54 ± 3 d). In addition, pigs (n = 5; 5.9 kg; age = 19 ± 3 d) were killed at the start of Exp. 2 to establish baseline (BL2) measurements, and liver Key Words: Growth, Iron Regulatory Protein, Pig, Transferrin, Whole Body 2005 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2005. 83:2137–2145 Introduction The use of an exogenous Fe source to prevent Fe deficiency in young pigs has been well documented (Ull- rey et al., 1959; Pollmann et al., 1983), and it is standard 1 Partially funded by Initiative for Future Agriculture and Food Systems grant. 2 Our laboratory thanks P. M. Coussen and M. E. Doumit for their assistance with laboratory techniques. 3 Correspondence: 2209 Anthony Hall (phone: 517-355-9676; fax: 517-432-0190; e-mail: hillgre@msu.edu). Received February 16, 2005. Accepted June 3, 2005. 2137 samples were collected and analyzed for IRP RNA bind- ing activity. In Exp. 1, no difference (P = 0.482) was observed in ADG. On d 13, Fe-treated pigs had greater (P = 0.001) Hb, Hct, and PFe and less (P = 0.002) Tf than Sal-treated pigs. Whole-body Fe concentration was greater (P = 0.002) in Fe- vs. Sal-treated pigs. Treated pigs (Fe or Sal) had greater (P = 0.006) whole- body Cu and less (P = 0.002) whole-body Ca, Mg, Mn, P, and Zn concentrations than BL1. Liver Fe concentra- tion was greater (P = 0.001) in Fe- vs. Sal-treated pigs, but liver Fe concentration of Sal-treated pigs was less (P = 0.001) than that of BL1 pigs. Sal-treated pigs had greater (P = 0.004) spontaneous IRP binding activity than Fe-treated pigs. In Exp. 2, spontaneous and 2-ME inducible IRP binding activities were greater (P = 0.013 and 0.005, respectively) in pigs fed diets containing 0 vs. 150 mg of added Fe/kg of diet. Moreover, pigs fed either treatment for 35 d had greater (P = 0.001) 2-ME inducible IRP binding activity than BL2 pigs. Results indicate that IRP binding activity is influenced by Fe supplementation. Subsequently, other indicators of Fe status are affected via the role of IRP in posttranscrip- tional expression of Fe storage and transport proteins. practice in the swine industry. Iron regulatory proteins (IRP) are RNA binding proteins that control the post- transcriptional expression of proteins required for the uptake, storage, and use of Fe (Eisenstein, 2000). Located within the cytoplasm, IRP bind to a highly conserved, 28-bp nucleotide sequence known as an iron responsive element (IRE) sequence (Aziz and Munro, 1987). Examples of proteins whose transcribed mRNA contain an IRE include erythroid-aminolevulinate syn- thase (eALAS), mitochondrial aconitase (m-acon), transferrin receptor (TfR), ferroportin, and ferritin (Eisenstein, 2000). Depending on the location of the IRE in either the 5′- or 3′-untranslated region (UTR) of mRNA, binding of an IRP to IRE inhibits or stabilizes