Effects of organic and inorganic iodine supplementation on the performance and immune response of feedlot cattle

Objectives investigated in these experiments were: (1) sensitivity of footrot causative organisms (Fusobacterium necrophorum [FN] and Bacteroides melaninoaenicus [BM]) to different I compounds; (2) effects of I supplementation on phagocytic ability of murine macrophages; and (3) effects of I supplementation in steers on immune response, serum I, triiodothyronine (T4) and thyroxine (T3) , performance and experimentally induced footrot.

Agar dilution and macrobroth procedures indicated that NalOj was more efficacious (P < .001) than Nal, KI, and EDDI against FN and BM (minimum inhibitory concentration =128 vs. 16,384 nq I/ml). Phagocytic ability of murine peritoneal resident macrophages (n = 42; purified diets plus 1.5, 3, and 6 ppm I from NalOj, Nal, and EDDI for 21 d) was higher (P < .05) for I fed mice. There were no differences (P > .2) among I sources and levels.

Steers (n = 28) fed I from EDDI, 03(103)2 and EDDI + 03(103)2 (0 to 36 ppm) had 8.6, 6.7 and 6.3 µg/dl increases (P < .001; r^2 > .95) in serum I/ppm supplemental I, respectively. Steer performance was not (P > .2) affected. Steers (n = 126) were fed EDDI, NaI03 and Nal (3 or 6 ppm; 2 X 3 factorial) for 170 d. No differences (P > .2) were noted in antibody titer (Brucella abortus Strain 19). Three steers per treatment were challenged with epidermal injections of phytohemagglutinin with protein (PHA-P, 200 /Ltg/steer) after 170 d. Steers fed EDDI and NalOj gave a more prolonged response (P < .05) than Nal fed and control steers. A lymphocyte transformation assay showed no difference (P > .2) among I treatments. Dry matter intake (DMI) was higher (P < .05) for EDDI than NaI03 and Nal fed steers. Steers fed control diets had higher DMI (8.1 vs. 7.6 kg/d, P < .01) and tended to have lower gain efficiency (132 vs. 141 g/kg, P = .11) than steers supplemented with I, Footrot was induced by scarification of interdigital skin and intradermal injection of a mixed culture of FN, BM and Corvnebacterium pyogenes in 33 of 34 attempts. No differences (P > .2) were noted among I treatments in intensity of footrot, possibly due to the severe procedures used. In conclusion, no undesirable effects were observed from prolonged I supplementation, I may affect the immune system as evident from the increased phagocytic ability of murine macrophages and greater induration response to PHA-P in cattle. Inorganic I sources gave similar serum I levels and are as effective as EDDI, immunologically.