Ruminant neonates require the passive acquisition of maternal immunoglobulins (Ig) derived from colostrum, to confer immunity against infectious disease in early life. Excess iodine in the diet of the pregnant dam is known to negatively affect neonatal serum IgG concentrations. This experiment examined the mechanisms underpinning the reduced IgG in the progeny of iodine supplemented dams at 24h postpartum. In a randomized complete block design, twin bearing ewes were split into 2 dietary groupings (n = 32 per group). The first group had no iodine supplement and the second was supplemented with 26.6mg per ewe per day of supplementary iodine in the form of calcium iodate for the final 4 weeks of gestation. Ewes were hand milked at 1, 10, and 18 h postpartum and colostrum intake of the lambs was recorded. At 24h postpartum a subset of lambs (n = 12 per group) were euthanized. Duodenal and ileal sections were collected to determine morphology and the expression of a panel of genes associated with antibody transfer. At 24h postpartum and fortnightly until 28 d postpartum IgG concentration was quantified from the serum of the remaining progeny. Iodine supplementation had no effect on colostrum yield, composition or lamb colostrum intake within the first 18h postpartum (P > 0.05). Despite this, the progeny from the iodine-supplemented ewes had lower serum IgG concentrations up until d 28 postpartum (P > 0.001) when compared with the progeny of the non-supplemented dams. Progeny of supplemented dams had increased expression of PIGR and FCAMR while the expression of B2M, THRB and ALB declined in the ileum when compared with non-supplemented progeny (P < 0.05). A reduction in villus height and villus height:crypt depth ratio was observed in the ileum of the supplemented progeny (P < 0.01). In conclusion, the results of this study presents novel data describing the relationship between maternal iodine nutrition and the subsequent failure of passive transfer leading to reduced serum IgG concentrations