A high dietary iodine increases thyroid iodine stores and iodine concentration in blood serum but has little effect on muscle iodine content in pigs.

There is still iodine deficiency in many populations, which justifies efforts to increase this trace element in food such as milk, eggs and meat by fortifying compound animal feeds with extra iodine. The iodine requirement of growing pigs is in the order of 100-200µg/kg feed (as a supplement) and the effects of this dosage range or higher on pork iodine concentration should be determined including the action of relevant iodine antagonists in feed, e.g., rapeseed. In three experiments on a total of 208 pigs [Pietrain×(Landrace×Large White)] the iodine concentration of meat (m. longissimus) - 71 samples -, blood serum - 100 samples - and of the thyroid - 100 samples - was analysed by intracoupled plasma-MS. In Experiment 1, 4×10 pigs received diets without or with rapeseed cake (0 and 3.2mmol glucosinolates/kg diet) either with 125 or with 250µg iodine/kg. In Experiment 2, the three groups with 46 pigs each were fed high iodine diets (1200µg supplementary iodine/kg) without or with 100 or 150g solvent extracted rapeseed meal/kg diet (0; 0.8 and 1.2mmol glucosinolates/kg). In Experiment 3, 3×10 pigs received either 600µg iodine/kg feed (1) or the 5-fold dosage (600+2400µg iodine/kg diet) administered 7 days (2) or 18 days (3) before slaughtering. The group means of pork iodine content were in the relatively small range from 3 to 16µg/kg, which contrasted to the enormously varying dosage range from 125 to 3000µg iodine/kg diet. There was a certain iodine dosage effect in Experiment 3 when - in comparison to the control - a 3-fold higher meat iodine concentration resulted from a 5-fold higher diet iodine concentration. In Experiment 1 with the low iodine offer, rapeseed cake with glucosinolates decreased the serum iodine level whereas in Experiment 2 this did not happen due to higher iodine fed and lower glucosinolates exposure. The thyroid iodine reflected the dietary iodine better than blood serum iodine and the serum better than muscle. However, in Experiment 2, 1200µg iodine/kg diet produced only half the serum iodine concentration than half as much dietary iodine in Experiment 3 (600µg iodine/kg diet), which may result from rapid elimination of blood iodine and a higher urinary excretion by longer duration of feed withdrawal before blood sampling. The muscle of pigs has to be classified as a low iodine food. Thus, there are no possibilities to concentrate this trace element reproducibly in amounts relevant for human nutrition in pork.

Pilot study: tendency of increasing iodine content in human milk and cow's milk.

The iodine supply in Germany has improved throughout the last decade, albeit with enormous differences between individuals and regions. In the Thuringian city of Jena, analyses of the iodine content of human milk have been undertaken regularly since 1982. Significantly increasing iodine concentrations in human and cow's milk have been found. Therefore, the current situation and the effectiveness of measures to prevent iodine deficiency demands re-evaluation. The iodine content of human milk from 32 lactating mothers was analysed on the 5th day (mean) postpartum and mothers' dietary iodine intake during the last two months of pregnancy was assessed by means of a food frequency questionnaire. To corroborate the assumption that the increasing iodine levels of cow's milk are one of the main reasons for the improved iodine supply, the iodine concentration of 34 cow's milk bulk-samples was also determined. Both human and cow's milk samples were analysed by the ICP-MS method. Twenty women took iodine supplements (mean daily intake = 175 microg). The average daily iodine intake of the 20 supplemented and 12 non-supplemented women was 258 microg and 116 microg, respectively. Daily iodine intake from food and beverages was significantly lower in supplemented women (83 microg/day). The average iodine content of human milk was 169 +/- 88 microg/l with a range of 33 - 348 microg/l. This content is two times higher than levels from 1994 in the same area. There was no difference in the human milk iodine content between mothers taking supplements and those who did not. Cow's milk samples showed a mean iodine concentration of 178 +/- 131 microg/l (range 48 - 661 microg/l).

Functional and morphological aspects of thallium-induced nephrotoxicity in rats.

Until now the effect of thallium (Tl) on renal function has not been investigated systematically. Therefore, the dose (5, 10, 15, 20 mg Tl2SO4/kg body wt., intraperitoneally) and time-dependence of renal damage was investigated in diuresis experiments on conscious rats. Morphology was evaluated after perfusion fixation in situ. Morphologic changes were localized in the thick ascending limb of the loop of Henle, mostly expressed at the 2nd day after Tl administration, which were completely normalized again at the 10th day. Other parameters such as Tl concentration, changes in water content and the activity of Na+/K(+)-ATPase as well as the diuretic effect of furosemide confirmed the Tl effect to be localized in the renal medulla. One single Tl administration is followed by a decrease in glomerular filtration rate (GFR) and urine volume and an increase of proteinuria. Electrolyte excretion was only slightly changed. All changes were reversible within the 10-day investigation period.

Bioavailability of iodine from normal diets rich in dairy products--results of balance studies in women.

During the last decade the iodine supply in Germany has increased significantly, but there is still a high frequency of goitre. Therefore the question of iodine bioavailability has arisen. In a two-period study 12 women were given a mixed diet of ordinary foods with milk and milk products of different batches. None of the volunteers suffered from an iodine deficiency according to WHO-criteria. Each period ended with a 9-day balance-study protocol in which all foods were provided. Food and fluid intake were registered, and urine and faeces were quantitatively collected. The iodine content was determined by ICP-MS. The mean intake in the form of solid food amounted to 175 +/- 10 micrograms I/d and to 27 +/- 15 micrograms I/d in fluid form. Milk and dairy products represented the main source of iodine (37%). Iodine was predominantly excreted in the urine (89%, 171 +/- 45 micrograms I/d) and the faeces 11% (20 +/- 11 micrograms I/d). The resulting iodine balance was approximately . In one case an iodine-rich erythrosine preparation with a low iodine bioavailability was used. Between the two periods of consuming different batches of milk and milk products no differences were observed concerning the high bioavailability of iodine.

[Iodine and thyroid hormone status of mother pigs and their offspring]. / Zum Jod- und Schilddrüsenhormonstatus von Mutterschweinen und ihren Nachkommen.

The iodine concentration in the chain sow feed-->blood serum of dams-->milk-->blood serum of piglets (2 per litter) was determined in 36 litters in two experiments with different dietary iodine levels and in 16 litters in the framework of field studies in two piglet production farms in each case at weaning after four weeks lactation. In the blood serum also the concentration of thyroxine (T4) and triiodothyronine was determined. The serum concentration of iodine and T4 did not indicate dietary iodine administration (sows) or showed only a weak response (piglets). The iodine concentration of milk was very strongly affected by iodine administration and by the iodine status of sows prior to the experiments. The highest milk iodine concentration was found in the sows of piglet production farms, corresponding to the level of iodine administered. For diagnosis of the iodine supply status the iodine concentration of sow milk should be analyzed. The lower limit of milk iodine concentration is presently defined as 50 micrograms/l, and the mean of 5 random samples per sow herd should not fall below this limit. Serum concentrations of iodine and T4 may remain moderate even in case of a low iodine supply (sow serum: 30 micrograms iodine/l, 25 nmol T4/l; piglet's serum: 50 micrograms iodine/l, 55 nmol T4/l), and are unsuited for diagnosis of iodine status.

Iron content in musculus longissimus lumborum et thoracis (m.l.l.t.) of fattening pigs.

Pork is among the most essential dietary sources of iron in Germany, considering its beneficial absorption rate. During 1997 and 1998 meat samples from 52 pigs per year were collected at the Thuringian performance testing station in order to examine the total iron content of pork. Musculus longissismus lumborum et thoracis (13./14. thoracic vertebra) from the right side of the carcasses were prepared for analyses. The total iron content was measured by atomic emission spectroscopy with inductively coupled plasma. The iron content of the meat was 4.18 +/- 0.97 mg/kg fresh material. This result was significantly lower than corresponding data from literature. An influence of the genetic composition of the pigs examined on the total iron content could be observed. The daily gain (R = -0.26) and intramuscular fat content (R = -0.28) were inversely correlated to the iron content. However, the lean meat proportion (R = 0.26) as well as haem pigment content (R = 0.27) were directly correlated to the total iron content of the meat.

Effect of rapeseed feedstuffs with different glucosinolate content and iodine administration on gestating and lactating sow.

In two experiments with a total of 60 sows during late pregnancy and at 28 days of lactation, diets containing rapeseed were compared with rapeseed free diets (control). In Experiment 1 dietary content of solvent extracted rapeseed meal was 250 g/kg (10 mmol glucosinolates/kg diet), in Experiment 2 diets containing 100 g/kg rapeseed were tested (2 mmol glucosinolates/kg diet). During late pregnancy all sows received 150 micrograms supplementary iodine/kg diet. In lactation, different subgroups received different rates of iodine administration (Exp. 1:0, 100 or 1000 micrograms/kg diet; Exp. 2: 0, 150 or 300 micrograms/kg diet). Rapeseed feeds had no significant effect on feed intake, body weight of sows and rearing parameters in both experiments. There was a tendency (8%) toward lower litter weight at weaning in Exp. 1. Sow diets without supplementary iodine but containing glucosinolates (via rapeseed meal, rapeseed) caused significant reduction in thyroxine serum concentration of piglets, whereas this hormone did not change in sow serum. Thiocyanate was significantly increased in the serum of mothers. The minor increase of thiocyanate concentration of milk and piglets' serum points to negligible transfer of rapeseed glucosinolate degradation products to offspring. However, the milk iodine concentration was significantly decreased due to glucosinolates, and this seems to be the reason for impaired iodine and thyroid hormone status of piglets from sows given rapeseed feeds.

Effects of rapeseed-press cake glucosinolates and iodine on the performance, the thyroid gland and the liver vitamin A status of pigs.

Rapeseed press cake (per kg DM 181 g EE, 341 g CP and 23.3 mmol glucosinolates) was tested in a long-term experiment with a total of sixty pigs (live weight range 24 to 104 kg). The 3 x 2 factorial design consisted of three rapeseed press cake levels (no rapeseed press cake--control, 75 g or 150 g rapeseed press cake per kg diet) each with two iodine dosages (125 or 250 micrograms supplementary iodine per kg diet). Reduced feed intake and depressed weight gain were found in groups receiving 150 g rapeseed press cake per kg diet, which correspond to 3.2 mmol glucosinolates per kg diet. At an inclusion level of 75 g rapeseed-press cake per kg diet no differences in feed intake and growth intensity were recorded in comparison to the rape feed free control. The rapeseed-press cake diet increased the weight of thyroid gland and liver and decreased the serum thyroxine (T4) concentration. Higher iodine dosage increased the serum T4 concentration of pigs receiving 75 g rapeseed press cake per kg diet (= 1.6 mmol glucosinolates per kg diet) to the level of the control group and retarded the enlargement of the thyroid gland. Intake of rapeseed products lowered the iodine content of the thyroid gland, however, there was no significant difference between groups given 1.6 and 3.2 mmol glucosinolates per kg diet. The vitamin A content of the whole liver and the vitamin A serum concentration were not influenced by the diets tested. However, rapeseed press cake and the glucosinolates, respectively, decreased the vitamin A concentration per gram liver due to the organ enlargement and the resulting dilution effect.

Rapeseed glucosinolates and iodine in sows affect the milk iodine concentration and the iodine status of piglets.

I in the chain sow diet --> blood serum of sow --> sow milk --> piglet serum was investigated in two experiments with a total of eighty-one sows and their piglets. In experiments conducted during the last trimester of gravidity and the 28 d of lactation, diets with glucosinolates (1.9 mmol/kg diet via 100 g ground rapeseed/kg diet (Expt 1) and 2.1 and 4.2 mmol/kg diet via 75 and 150 g rapeseed press cake/kg diet (Expt 2)) were compared with control groups without rapeseed products. From 0 to 600 microg I/kg was added to sow diets during lactation. Diets without supplementary I decreased the I concentration particularly in milk and piglet serum. The presence of rapeseed and rapeseed press cake were indicated by a thiocyanate concentration increase, mainly in sow serum. The diets with glucosinolates decreased the milk and piglet serum I concentration. Spot urine and faeces samples from sows eating the rapeseed-press cake diets had increased I concentration. The sows' serum I and thyroxine did not respond to glucosinolates (Expt 1) or these diets caused an increase in concentration (Expt 2). Both these criteria seem unsuitable for the diagnosis of I status of adult animals. Glucosinolates and their degradation compounds may affect the thyroid and the mammary glands resulting in lower I milk transfer and higher renal and intestinal I excretion.