Levels Of Iodine Supplementation Research Articles

Iodine contrast exposure and incident COVID-19 infection.

Iodine and particularly its oxidated forms have long been recognized for its effective antiseptic properties. Limited in vitro and in vivo data suggest that iodine exposure may rapidly inactivate, reduce transmission, and reduce infectivity of SARS-CoV-2. We hypothesized that iodine exposure may be associated with decreased incident COVID-19 infection. A retrospective population-level cohort analysis was performed of the U.S. Veterans Health Administration between 1 March 2020 and 31 December 2020, before the widespread availability of vaccines against SARS-CoV-2. Multivariable logistic regression models estimated the adjusted odds ratios (OR) and 95% confidence intervals (CI) of the associations between iodinated contrast exposure and incident COVID-19 infection, adjusting for age, sex, race/ethnicity, place of residence, socioeconomic status, and insurance status. 530,942 COVID-19 tests from 333,841 Veterans (mean ± SD age, 62.7 ± 15.2 years; 90.2% men; 61.9% non-Hispanic Whites) were analyzed, of whom 9% had received iodinated contrast ≤60 days of a COVID-19 test. Iodine exposure was associated with decreased incident COVID-19 test positivity (OR, 0.75 95% CI, 0.71-0.78). In stratified analyses, the associations between iodinated contrast use and decreased COVID-19 infection risk did not differ by age, sex, and race/ethnicity. Iodine exposure may be protective against incident COVID-19 infection. Weighed against the risks of supraphysiologic iodine intake, dietary, and supplemental iodine nutrition not to exceed its Tolerable Upper Limit may confer an antimicrobial benefit against SARS-CoV-2. A safe but antimicrobial level of iodine supplementation may be considered in susceptible individuals, particularly in geographic regions where effective COVID-19 vaccines are not yet readily available.

Iodine Concentrations in Conventional and Organic Milk in the Northeastern U.S.

Milk is a major source of dietary iodine in the United States. Due to a relatively low margin of safety for iodine intake, there are concerns for both deficiency and over-exposure. Iodine concentrations of raw milk samples from farms and retail milk in the Northeastern U.S. region were compared between seasons (winter vs. summer) and farming practices (conventional vs. organic). Overall, mean iodine concentration was 46.2% higher in raw milk from conventional farms vs. organic farms. An interaction effect between season and farming practices was observed. Organic raw milk had higher iodine content in the winter than in the summer (423 ± 54 μg/L vs. 273 ± 24 μg/L), whereas conventional raw milk had higher iodine content in the summer than in the winter (618 ± 75 μg/L vs. 398 ± 27 μg/L). Milk samples from conventional farms had 2.27-fold higher average iodine concentration compared to milk coming from organic farms in the summer but did not differ in the winter. Out of 68 and 98 raw milk samples originating from conventional and organic farms, 22 (32.4%) and 19 (19.4%) respectively, had iodine concentrations > 500 µg/L, reaching as high as 1928 μg/L. In contrast, the overall mean concentration of iodine in retail milk did not differ between conventional and organic milk (345 ± 23 vs. 320 ± 42 μg/L, respectively). The current study confirms dairy milk remains to be a good source of iodine to U.S. consumers. However, dairy farms should be aware of the potential adverse health effects of excess iodine intake. Careful considerations in dairy management may be necessary to not exceed the recommended level of iodine supplementation in both conventional and organic operations at the farm level—to maintain optimal iodine concentrations in retail fluid milk accessible to the consumers.

The effects of dietary iodine and its consumption duration on performance, carcass characteristics, meat iodine, thyroid hormones and some blood indices in broiler chickens.

This study was conducted to determine the effects of dietary inclusion levels of iodine supplementation and duration of feeding on performance, carcass characteristics, meat iodine, thyroid hormones and some indices including red blood cell, haematocrit, haemoglobin, aspartate transaminase, alanine transaminase and alkaline phosphatase in broilers. A total of 450 one-day-old male broiler chicks were used during a 42days experiment in 9 treatments with five replicates pen for each treatment. The experimental design was a 3×3 factorial arrangement of treatments including three levels of iodine (0, 2.5 and 5mg/kg as a source of potassium iodide) during the T (total, 1-42days), GF (grower and finisher, 11-42days) and F (finisher, 25-42days) periods (p<.05). The results demonstrated that none of the performance data (feed intake, body weight gain and feed conversion ratio) were influenced by level and duration of iodine consumption (p>.05). The diet supplemented with 5mg/kg iodine had no effects on relative weights during total (T) and grower and finisher (GF) periods, but there was an effect on the finisher (F) period. Moreover, increasing the iodine level from 0 to 5mg/kg linearly decreased the relative weights of the both small intestine and jejunum (p<.05). Increasing the iodine level from 0 to 5mg/kg linearly increased the breast iodine content. Also, the highest breast meat enrichment was observed during the T period (p<.05). Blood triiodothyronine concentration was not changed by any of the iodine level and duration of consumption, but tetraiodothyronine concentration was higher for T period than GF and F ones (p<.05) and even linearly increased by increasing the level of dietary iodine for 0 to 5mg/kg (p<.05). It was concluded that 5mg/kg iodine from day 1 to day 42 of age is needed in the diet to enrich the broiler meat.

Does the iodized salt therapy of pregnant mothers increase the children IQ? Empirical evidence of a statistical study based on permutation tests

The nutritional iodine deficiency disorders are still a major health problem in industrialized countries, but they are completely preventable by means of iodine prophylaxis. Iodine is essential for thyroid hormone (TH) synthesis and TH is required for normal brain development. Gestational iodine supplementation may improve infant cognitive development. In this study we aimed at evaluating the intelligence quotient of children born to mothers with different levels of iodine supplementation, with or without the administration of levothyroxine (LT4), prior to and during pregnancy. In particular we focused our attention on some mother–child pairs and we compared them according to iodized salt consumption and LT4 treatment. In this specific context, NPC test was applied to compare four groups of children, defined on the basis of maternal history related to iodized salt consumption and LT4 treatment. The results show that the deficit in functionality cognitive (in terms of intelligence quotient) is significantly higher in the children of mothers that does not make supplementation of iodized salt. This shows how a lack of iodine can hinder children in reaching their full intellectual potential. From a methodological point of view, our research showed the utility of the Non Parametric Combination test (NPC test) into analyze data concerning medical research.

Effect of dietary iodine on production of iodine enriched eggs.

Aim:Objective of this study was to investigate the effect of different levels of iodine supplementation on iodine content of eggs in laying hens.Materials and Methods:In the experiment, 135 laying hens (White Leghorn) of 55 weeks age were randomly distributed to 5 dietary treatments; each group contained 27 laying hens distributed in three replicates of 9 birds each. Diet T1 was control basal layer diet without iodine enrichment in which iodine content (I2) was as per NRC recommendation. Basal diets were supplemented with calcium iodate (Ca (IO3)2) at 5, 10, 15 and 20 mg/kg in T2, T3, T4 and T5 groups, respectively. The iodine content in the calcium iodate is 65.21%, therefore, the diets T2, T3, T4 and T5 contained 3.25, 6.50, 9.75 and 13.0 ppm iodine, respectively. The laying hens were fed the respective experimental diets ad libitum during the experimental period of 10-week. The iodine content of egg yolk and albumen was analyzed at the end of 5th and 10th week of the experiment. Economics of feeding for the production of iodine enriched egg was calculated at the end of the experiment.Results:Increasing iodine levels in diet of hens from 0.45 to 13.0 ppm significantly increased egg iodine concentration, the highest concentration of egg iodine was observed in the group fed diet supplemented with 13.0 ppm iodine followed by those fed 9.75, 6.50, 3.25 and 0.45 ppm iodine in diet. There was no significant difference in the iodine levels of unboiled versus boiled eggs. Therefore, the consumers are ensured to receive the optimal levels of iodine from boiled iodine-enriched eggs. Among different diets, minimum and significantly lower feeding cost (Rs. per dozen or per kg eggs) was noticed in hens allotted T3 diet (6.50 ppm I2). However, feeding cost of hens receiving 3.25 and 9.25 ppm I2 was statistically (p<0.05) similar to control group (T1). Further, it was noticed that feeding cost (Rs. per dozen or per kg eggs) was significantly increased due to the inclusion of higher level of iodine (13.0 ppm).Conclusion:It was concluded that supplementing iodine at 6.50 ppm in layers diet was economically better for the production of iodine enriched eggs followed by feed iodine supplementation at 3.25 ppm as compared to control and other treatment groups.

Effects of Maternal Iodine Nutrition and Thyroid Status on Cognitive Development in Offspring: A Pilot Study.

Maternal iodine nutrition and thyroid status may influence neurocognitive development in offspring. This study investigated the effects on the intelligence quotient (IQ) of children born to mothers with different levels of iodine supplementation, with or without the administration of levothyroxine (LT4), prior to and during pregnancy. This pilot, prospective, observational study included four study groups, each comprising 15 mother-child pairs, identified on the basis of maternal histories of iodized salt consumption and LT4 treatment prior to and during pregnancy. The groups were labeled as follows: iodine (I), no iodine (no-I), iodine + LT4 (I + T4), and no iodine + LT4 (no-I + T4). IQ tests were administered to children at 6-12 years of age with the Wechsler Intelligence Scale for Children-3rd Edition (WISC-III), with full-scale IQ (FSIQ), verbal IQ (VIQ), and performance IQ (PIQ) being evaluated. Children of I and I + T4 mothers had similar verbal, performance, and FSIQs, which were 14, 10, and 13 points higher, respectively, than children born to no-I and no-I + T4 mothers. A positive association was found between VIQ and maternal urinary iodine (β = 1.023 [confidence interval (CI) 1.003-1.043]; p = 0.028), but not with maternal free thyroxine concentrations at any stage of pregnancy. Overall, the prevalence of borderline or defective cognitive function was more than threefold higher in the children of mothers not using iodized salt than of those mothers using it (76.9% vs. 23.1%, odds ratio 7.667 [CI 2.365-24.856], χ2 = 12.65; p = 0.0001). Neuro-intellectual outcomes in children appear to be more dependent on their mothers' nutritional iodine status than on maternal thyroid function. These results support the growing body of evidence that prenatal, mild-to-moderate iodine deficiency adversely affects cognitive development later in life, with a seemingly greater impact on verbal abilities.

Iodine supplementation and drinking-water perchlorate mitigation

Ensuring adequate iodine intake is important, particularly among women of reproductive age, because iodine is necessary for early life development. Biologically based dose–response modeling of the relationships among iodide status, perchlorate dose, and thyroid hormone production in pregnant women has indicated that iodide intake has a profound effect on the likelihood that exposure to goitrogens will produce hypothyroxinemia. We evaluated the possibility of increasing iodine intake to offset potential risks from perchlorate exposure. We also explored the effect of dietary exposures to nitrate and thiocyanate on iodine uptake and thyroid hormone production. Our modeling indicates that the level of thyroid hormone perturbation associated with perchlorate exposures in the range of current regulatory limits is extremely small and would be overwhelmed by other goitrogen exposures. Our analysis also shows that microgram levels of iodine supplementation would be sufficient to prevent the goitrogenic effects of perchlorate exposure at current regulatory limits among at risk individuals. The human health risks from supplementing drinking water with iodine are negligible; therefore, this approach is worthy of regulatory consideration.

Influencing factors on iodine content of cow milk

Iodine is an essential trace element for humans and animals, and it is incorporated into the thyroid hormones such as thyroxine and triiodothyronine, which have multiple functions in energy metabolism and growth, but also as transmitter of nervous stimuli and as an important factor for brain development. Because of the small range between iodine requirements and the upper level for humans (between 1:2.5 and 3), the requirements should be met, but excesses should be avoided. One of the most important iodine sources for humans is milk of ruminants. Therefore, various influencing factors on the iodine content of milk of ruminants should be analyzed in the paper. The iodine content of milk depends on many factors, such as iodine content and level of iodine supplementation of feed, iodine source, iodine antagonists such as glucosinolates in the feed, farm management, teat dipping with iodine-containing substances, and milk processing in the dairy. The effects of some factors on the iodine content of milk are demonstrated and discussed. Feed iodine supplementation has the main effect on milk iodine. However, the iodine content of milk may vary considerably depending on many other influencing factors. As a consequence of preventive consumer protection, the European Food Safety Authority proposed a reduction in the iodine upper level for lactating ruminants from 5 to 2 mg/kg complete feed.

Estimating the iodine supplementation level to recommend for pregnant and breastfeeding women in Australia

To identify a level of iodine supplementation to recommend for pregnant and breastfeeding women in Australia. Dietary modelling indicated that mandatory fortification of bread with iodine by replacing salt with iodised salt would still leave a gap in iodine intakes in pregnant and breastfeeding women in Australia. Iodine shortfall was estimated by two separate methods: (i) analysis of data from published studies reporting mean urinary iodine concentrations in populations of Australian women who were pregnant or had given birth in the past 6 months; and (ii) modelling based on the postmandatory fortification iodine intake estimates calculated by Food Standards Australia New Zealand using food consumption reported by women aged 19-44 years who participated in the 1995 National Nutrition Survey. Estimated level of daily supplementation required to provide sufficient iodine to result in a low proportion of pregnant and breastfeeding women having inadequate iodine intakes. Estimations from both data sources indicate that a supplement of 100-150 μg/day would increase iodine intakes to a suitable extent in pregnant and breastfeeding women in Australia. The final level of supplementation we recommend should be based on these calculations and other factors. There will be population subgroups for whom our general recommendation is not appropriate.

Iodine and selenium carry over in milk and cheese in dairy cows: effect of diet supplementation and milk yield

Iodine and selenium are essential trace elements involved in the regulation of thyroid metabolism and antioxidant status. Two experiments were undertaken on lactating cows to determine the milk concentrations of iodine and selenium, carry over (CO) in milk, the fraction in curdle portion and how milk yield affects the milk iodine and selenium concentrations and CO. Sources of elements were potassium iodide and sodium selenite. In Experiment 1, 12 cows were randomly allotted to three diet groups in a completely randomized design: control group (CTR) – total mixed ration (TMR) containing 1.71 and 0.08 mg/kg dry matter (DM); Group 1 (T1) – TMR plus 23.8 and 2.2 mg; Group 2 (T2) – TMR plus 45.5 and 4.3 mg, respectively, for iodine and selenium. In Experiment 2, 30 cows were allotted to three groups according to milk yield: high (H), average (A) and low (L). Within each group, cows were randomly assigned two levels of iodine and selenium: Level 1: TMR containing 1.55 and 0.15 mg/kg DM; Level 2: TMR plus 47.2 mg and 8.0 mg, respectively, iodine and selenium. In both experiments, individual milk samples were collected and analyzed for iodine and selenium contents. In Experiment 1, Grana Padano cheese was obtained at lab scale and the iodine and selenium fractions in the curd were measured. In Experiment 1, the iodine intake increased (P < 0.001) the concentration and total excretion in milk. The CO increased (P < 0.05) from 16 (CTR) to 27 (T1) and 26% (T2); the sampling time was significant (P < 0.05) with no interaction with treatments. Concentration of selenium in milk was increased (P < 0.05) by treatment and CO decreased (P < 0.01) from 26 (CTR) to 12 (T1) and 9% (T2). The iodine showed a mild enrichment factor in the curdle (about 1.7-fold), whereas selenium enriched five- to sevenfold. In Experiment 2, the level of iodine supplementation affected (P < 0.05) the concentration and total excretion in milk. No effects on milk iodine concentration were related to milk yield or milk yield × treatment interaction; however, the iodine excretion in milk was major (P < 0.05) in higher yielding groups. The iodine CO was affected (P < 0.05) by the milk yield in supplemented groups. The selenium milk concentration and excretion were affected (P < 0.01) by the milk yield, whereas the CO was affected (P < 0.05) by the milk yield and selenium supplementation. Results highlight the possibility of fortification with iodine in milk and selenium in cheese through animal feeding.

Iodine content of mother’s milk – Hungarian representative survey, 2006

In Hungary, except for some small area, iodine content of soil, cultivated crops and potable water is low; therefore the iodine intake of Hungarian population is lower than the amount recommended by international organizations. The high iodine intake for pregnant and nursing women is important to ensure the appropriate iodine intake of fetus and nursing babies, as well. The objective of the study was to get a comprehensive picture of iodine content of mother's milk and to make recommendation for the level of iodine supplementation for pregnant and nursing women. Following a country-wide sampling, iodine content of 72 human milk samples were analyzed by inductively coupled plasma-mass spectrometry. Iodine intake in 42 percent of babies is lower than the recommended amount which could remarkably influence the physical and mental development of infants. Iodine supplementation and consumption of food with high iodine content is highly recommended during pregnancy and nursing.

Iodine carry over in dairy cows: effects of levels of diet fortification and milk yield

Thirty multiparous lactating cows were divided in three groups based on milk yield: high (H), average (A) and low (L). Within each group, cows were randomly allotted to two levels of iodine inclusions into the diet and respectively: level 1 (1): base diet containing 1.55 mg/kg dry matter, level 2 (2): base diet plus 47.2 mg/d. Potassium iodide was used. Feeds, orts, drinking water and individual milk samples were collected and analysed for the iodine content. The iodine concentration and total excretion in milk were affected by the level of iodine supplementation (P<0.05). No effect on milk iodine concentration could be addressed either to the level of milk yield or to the milk yield x treatment interaction. The total amount of iodine excretion and carry over were affected (P<.05) by the level of milk yield.

Effect of iodine supplementation on thyroid and testicular morphology and function in euthyroid rats

Seventy-five male weaner euthyroid rats, randomly divided into three equal groups were used to evaluate the effect of iodine supplementation in the diet on growth and spermatogenesis. From the age of six weeks, the rat groups were fed normal diet containing 0.05 mg iodine/Kg diet (A); normal diet supplemented with 0.5 mg/Kg iodine (B) and normal diet supplemented with 3.0 mg/Kg iodine for a period of 90 days. Thereafter, all three groups were fed the normal diet for another 60 days. Body weight and feed consumption were determined; morphomeric studies of thyroid glands, testes and epididymes were carried out. Spermatogenesis was evaluated with epididymal (ESC) and testicular sperm counts (TSC). Increasing iodine intake significantly (p < 0.05) decreased mean body weight from day 30 of supplementation. Iodine supplementation influenced feed conversion ratio and efficiency in feed utilization in an inconsistent pattern. Supplementation did not significantly (p > 0.05) alter the size of thyroid glands, but increased the mean weights of the testes and epididymes to levels significantly (p < 0.05) higher than values for non-supplemented rats at specific stages of the study, especially at the highest (3 ppm) level of iodine supplementation. However, supplementation resulted generally in lower sperm counts, which was significant (p < 0.05) in the case of the epididymes. The results of the study show that iodine supplementation to weaner, non-iodine deficient euthyroid rats at 3ppm not only retard weight gain but could also reduce fertility by lowering epididymal sperm counts.

Effect of dietary iodine on growth and iodine status of growing fattening bulls

The aim of the present study was to assess the influence of different levels of iodine supplementation on animal growth and the iodine content of food from beef cattle. In a dose–response experiment with 34 growing fattening bulls of the “German Holstein” breed, in the range from 223 to 550 kg body weight, three iodine dosages were tested. The animals were fed a corn silage/concentrate ration. Iodine concentration in the diet amounted to 0.79 (Group 1), 3.52 (Group 2) and 8.31(Group 3) mg I per kg dry matter (DM). After slaughtering, I was determined in blood, serum, plasma, thyroid, liver, kidneys and meat (M. longissimus dorsi, M. glutaeus medius) by ICP-MS. I-supplementation did not significantly influence DM intake, daily weight gain (1453 (1), 1419 (2) and 1343 (3) g; p>0.05) or slaughtering performance, but the weight of the thyroid gland increased significantly with the highest I dosage (32 (1), 26 (2) and 42 (3) g animal−1, p<0.05). I-supplementation significantly increased I-concentration in muscle, liver, kidney and thyroid gland (p<0.05). The contribution of beef food to I-intake of humans is relatively low, therefore there is no need to reduce the EU-upper limit (10 mg kg−1 feed) for growing fattening cattle from the view of consumer safety. In view of animal health and performance more dose–response studies seem to be necessary.

Lamb serum vitamin E and immunoglobulin G concentrations in response to various maternal mineral and iodine supplementation regimens

AbstractThe objective of the first of three studies (experiment 1) was to evaluate the effects of supplementing the pregnant ewe diet with high levels of minerals for the final 4 weeks of gestation on lamb serum vitamin E and immunoglobulin G (IgG) concentration at 24 h post partum. Sixty ewes were allocated to one of two treatments (no. =30) and offered a basal diet fortified with 52 g of supplementary minerals/vitamins containing Ca, Mg, Na, P, Co, I, Mn, Se, Zn and vitamin E (M1) for the final 4 weeks of pregnancy or no mineral/vitamin supplement was added (C1). Immediately after birth, lambs were allocated to one of four treatments in a 2×2 factorial design with the factors being ewe treatment (± minerals) and colostrum origin (± minerals). Irrespective of the colostrum origin, the progeny of the mineral supplemented ewes had lower serum vitamin E and IgG concentrations and IgG absorption efficiency at 24 h post partum (P&lt;0·001). In a second study (experiment 2), 44 ewes were allocated to one of four treatments (no. =11) in week 13 of pregnancy and offered a basal diet in addition to one of the following mineral/vitamin fortifications: 0 g (C2), 52 g of a mineral supplement as in experiment 1 (M2), a supplement as in M1 but with iodine excluded (-I), iodine only offered at a rate (40 mg per ewe per day) equivalent to 52 g of minerals (IO). When iodine was offered either M2 (P&lt;0·01) or (IO) (P&lt;0·001) it resulted in the progeny having a reduced serum vitamin E concentration at 24 h post partum. The -I progeny had higher serum vitamin E concentrations at 24 h post partum than the progeny of treatments C2, M2 (P&lt;0·01) and IO (P&lt;0·001). In a third study (experiment 3) the effect of incremental levels of iodine supplementation on lamb serum vitamin E concentration was studied. Forty-eight ewes were allocated to one of four treatments (no. =12) and offered the following levels of supplementary dietary iodine: 0 mg (C3), 8·9 mg (LI), 17·7 mg (MI) or 26·6 mg (HI) for the final 6 weeks of pregnancy. There was a linear (P&lt;0·001) reduction in lamb serum vitamin E concentration as maternal iodine supplementation increased. We conclude that when ewes are offered high levels of iodine during the final 6 weeks of gestation their progeny are pre-programmed in utero to have a reduced ability to absorb colostral vitamin E. These findings support our earlier studies and provide further evidence of the need to reduce the current toxicity values for iodine. for the ewe in late pregnancy.

The effect of varying levels of mineral and iodine supplementation to ewes during late pregnancy on serum immunoglobulin G concentrations in their progeny

AbstractThree experiments were carried out to evaluate the effects of varying levels of mineral and iodine supplements when offered to ewes in late pregnancy on lamb serum immunoglobulin G (IgG) concentrations. In experiment 1, 44 individually housed ewes were allocated to one of four treatments (no. = 11) and offered a basal diet of grass silage ad libitum which was supplemented with 500 g/day of a concentrate (190 g/kg of crude protein (CP)), in addition to mineral/vitamin fortification at the rate of 0 g (C), 17.3 g (LM), 34.6 g (MM) or 52.0 g (HM) per day for the final 7 weeks of pregnancy. The mineral/vitamin supplement contained Ca, P, Na, Mg, Mn, Se, I, Co, Mn and vitamin E. The ewes were milked at 1 h, 10 h and 18 h post partum and measured quantities of colostrum, proportional to lamb birth weight, were fed back to the lambs via a stomach tube. Treatment had no effect on total colostrum yield or total IgG yield to 18 h post partum (P &gt; 0.05). There was a linear decrease in serum IgG concentration and IgG absorption efficiency as mineral supplementation increased (P &lt; 0.001). In experiment 2, which was carried out in conjunction with experiment 1, 44 ewes were allocated to four treatments (no. = 11) and offered the same basal silage/concentrate diet as in experiment 1, in addition to receiving one of the following supplements : (C) control, as in experiment 1; (HM), as in experiment 1; (−I), ewes offered the same mineral/vitamin supplement as HM but with iodine excluded; (I0), ewes offered a daily mineral supplement of iodine only at a level of 40 mg per ewe, equivalent to the iodine inclusion in the 52 g of minerals offered in HM. The iodine-supplemented progeny (HM and IO) had lower (P &lt; 0.001) serum IgG concentrations and higher soil scores (P &lt; 0.05) than the C and −I progeny. In experiment 3, the effects of varying levels of iodine supplementation when offered to ewes during the final 6 weeks of pregnancy on lamb serum IgG values were examined. Forty-eight individually housed ewes were allocated to one of four treatments (no. = 12) and offered grass silage ad libitum, which was supplemented initially with 500 g of a concentrate (140 g/kg of CP) from days 99 to 130 of gestation and then replaced with 700 g/day of a concentrate (180 g/kg of CP) from day 131 of gestation until lambing. In addition, the diet of each ewe was supplemented on a daily basis with iodine at the rate of 0 mg (C), 8.9 mg (LI), 17.7 mg (MI) or 26.6 mg (HI). There was a negative linear reduction in serum IgG concentration and IgG absorption efficiency as maternal dietary iodine supplementation increased (P &lt; 0.001). We conclude that supplementation of the ewe's diet in late pregnancy with 17.3 g of a mineral supplement as formulated in the current experiment lowers the lamb's ability to absorb colostral IgG, and offering only the iodine component of this mineral supplement, at a level which approximates to about one third of currently quoted toxicity levels, will result in reduced serum IgG concentration in the lamb. These findings suggest the need to re-examine current toxicity values for iodine.

THE EFFECTS OF THE LEVEL OF IODINE IN CANOLA MEAL CONCENTRATE ON MILK IODINE AND THIOCYANATE CONTENT AND THYROID FUNCTION IN DAIRY COWS

Six lactating heifers were used in a randomized block design to measure the effects of different levels of iodine supplementation in a canola meal (CM) based concentrate on milk iodine and thiocyanate content and thyroid function. The treatments were a pre-experimental control diet (diet C) and a concentrate containing 20% Tower CM (air-dry) with 1.2 (CM-1.2), 2.2 (CM-2.2), 3.3 (CM-3.3) and 4.5 (CM-4.5) mg supplemented iodine/kg concentrate dry matter. The same roughage mixture was fed with all diets. Cows were maintained on diet CM-1.2 for 5 wk, after which they were changed sequentially to diets CM-2.2, CM-3.3 and CM-4.5 at 3-wk intervals. Milk samples were taken and a thyrotropin-releasing hormone test was conducted before the start of the experiment and at the end of each period. Milk samples were also taken daily between days 2 and 6 after diet change-over during treatments CM-2.2, CM-3.3 and CM-4.5. Concentrations of iodide in milk (mean ± SE) for diets C, CM-1.2, CM-2.2, CM-3.3 and CM-4.5 were 42.0 ± 10.9, 9.2 ± 0.4, 11.1 ± 0.3, 14.5 ± 1.0 and 18.7 ± 1.2 μg/100 mL, respectively. Milk iodide content for the CM concentrate with different iodine levels was lower (P &lt; 0.01) than the pre-experimental control value. However, diets CM-3.3 and CM-4.5 successively increased (P &lt; 0.05) milk iodide content compared to diets CM-1.2 and CM-2.2. During the adaptation periods of diets CM-3.3 and CM-4.5, milk iodide content increased (P &lt; 0.05) rapidly compared to the previous treatment mean. Milk thiocyanate concentrations for the CM-1.2, CM-2.2, CM-3.3 and CM-4.5 diets were 134.8 ± 4.6, 135.3 ± 7.4, 117.3 ± 5.0, and 156.0 ± 6.7 μmoles/L, respectively. Thyroid function of the cows was not different among the different diets, being influenced by neither the CM nor level of iodine. Iodine supplementation of CM based concentrate at 3.3 and 4.5 mg/kg concentrate DM increased milk iodide concentrations, but not to pre-experimental levels. Milk iodide concentrations were normal during any treatment.