Iodine in the feed of cows and in the milk with a view to the consumer's iodine supply.

Milk may be an iodine source for humans, but its magnitude depends on the iodine content of cow feed. The present investigation focused on the iodine level of feed and milk in German feeding practice in comparison with the results of previous milk monitoring and dose-response experiments with dairy cows. In 73 samples of straight feedstuffs (41 concentrates, 32 silages prepared from grass or green maize) and a total of 83 vitamin mineral premixes and compound feeds, respectively, the iodine content was determined and along with the expected daily iodine intake of cows. In six Thuringian cow herds, the total cow diets (51 total mixed rations, TMR) as well as the bulk milk (n=77) were analysed for iodine. Cereal and legume grains and extracted meals from oilseeds had very low native iodine contents at<9-43µg iodine/kg dry matter (DM). Silages showed higher contents than the concentrates. In grass silage, the median amounted to 173µg iodine/kg DM. The significant relationship between the silages' ash and iodine content indicates contamination of grass during harvesting by soil. With regard to supplements, dairy cows received via premixes a mean of 1.2mg iodine/kg diet DM and this was in the magnitude of 0.8mg iodine/kg DM determined in TMR on farm. However, the resulting mean milk concentration of 105µg iodine/kg, median 100µg/kg, is only a half of that in dose-response experiments with 200µg iodine/kg milk at 1mg iodine/kg cow feed DM. The decrease of iodine transfer into the mammary gland and milk is caused by rapeseed meal (RSM) with the glucosinolates and their degradation compounds, e.g. isothiocyanates. By compensating for the iodine antagonist effects of diets containing RSM, more iodine should be added. Twice the current mean feed iodine supplement would optimize the contribution of animal-source food to the human iodine supply in Germany.

Effect of the desolventizing/toasting process on chemical composition and protein quality of rapeseed meal.

BACKGROUND: During processing in a desolventizer/toaster (DT), rapeseed meal (RSM) is heated to evaporate the hexane and to reduce the level of heat-labile anti-nutritional factors such as glucosinolates (GSL). However, excessive heat treatment may reduce amino acid (AA) content in addition to lower AA digestibility and availability in RSM. The objective of the present study was to produce from one batch of a 00-rapeseed variety (17 µmol GSL/g dry matter (DM), seed grade quality) five differently processed RSM under standardized and defined conditions in a pilot plant, and to determine the impact of these different treatments on protein solubility and chemical composition, in particular with regard to contents of AA including reactive Lys (rLys) and levels of total and individual GSL. METHODS: Four RSM were exposed to wet toasting conditions (WetTC) with increasing residence time in the DT of 48, 64, 76, and 93 min. A blend of these four RSM was further processed, starting with saturated steam processing (< 100 °C) and followed by exposure to dry toasting conditions (DryTC) to further reduce the GSL content in this RSM. RESULTS: The contents of neutral detergent fiber and neutral detergent fiber bound crude protein (CP) increased linearly (P < 0.05), as residence time of RSM in the DT increased from 48 to 93 min, whereas contents of total and most individual GSL and those of Lys, rLys, Cys, and the calculated ratio of Lys:CP and rLys:CP decreased linearly (P ≤ 0.05). The combination of wet heating and DryTC resulted in the lowest GSL content compared to RSM produced under WetTC, but was associated with lowest protein solubility. CONCLUSIONS: It can be concluded that by increasing residence time in the DT or using alternative processing conditions such as wet heating combined with DryTC, contents of total and individual GSL in RSM can be substantially reduced. Further in vivo studies are warranted to elucidate if and to which extent the observed differences in protein quality and GSL content between RSM may affect digestibility and bioavailability of AA in monogastric animals.

Influencing factors on iodine content of cow milk.

PURPOSE: 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. RESULTS: 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. CONCLUSIONS: 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.

Iodine concentration of milk in a dose-response study with dairy cows and implications for consumer iodine intake.

Most feed is poor in iodine and iodine supplementation of cow's diets must guarantee milk iodine concentrations for humans that contribute to prevention of the deficiency and minimize the risk of exceeding an upper limit of iodine intake. Five Holstein cows were fed four iodine doses (via Ca(Iota O(3))(2).6H(2)O). In four sequential 14-d periods, doses of 0.2 (basal diet), 1.3, 5.1, and 10.1 mg iodine kg(-1) diet dry matter (DM) were administered. Samples of milk were collected during each period; blood was also sampled from each cow for each iodine dosage. In an 18-d depletion period, a non-supplemented diet was provided. Iodine was determined by inductively coupled plasma-mass spectrometry. The iodine content of milk and serum reflected the iodine dosages in feed significantly. The levels for the four doses tested in milk were 101+/-32, 343+/-109, 1215+/-222, and 2762+/-852 microg iodine kg(-1). The total amount of iodine in milk per day was 30-40% of ingested supplemental iodine. Omitting additional iodine resulted in a short-term reduction of serum and milk iodine following an exponential decay function. The iodine supplementation of 0.5-1.5 mg kg(-1) diet DM represents the requirement of the cow, resulting in 100-300 microg iodine L(-1) milk, which optimally contributes to human supply. The maximum dietary levels of former and present EU legislations (10 and 5 mg iodine kg(-1) cow feed) increase the risk of iodine excess in humans.

Influence of dietary iodine on the iodine content of pork and the distribution of the trace element in the body.

BACKGROUND: Millions of people worldwide still suffer from iodine deficiency disorders. Besides salt iodination, iodine is added to animal feed to concentrate it in food of animal origin (milk, eggs, meat). Otherwise possible adverse effects of high supplementation should be avoided. AIM OF THE STUDY: The objective of the study was to evaluate the iodine content of pork at various feed iodine concentrations to estimate its contribution to human iodine supply. Furthermore the handling of low and high iodine dosages by the organism should be investigated using the pig as a model for the human. METHODS: Seventy pigs (live weight period 27-115 kg), divided into five groups, were fed diets supplemented with 0 (group 1), 0.5 (group 2), 1 (group 3), 2 (group 4) and 5 (group 5) mg iodine per kg diet. Iodine was determined in the thyroid and in the fractions innards/blood, bones and muscle/fat of four pigs of each group by ICP-MS. RESULTS: Rising iodine supplementation of feed significantly increased (P < 0.05) the iodine content of the muscle/fat fraction [3.9 (group 1), 6.0 (group 2), 8.5 (group 3), 10.8 (group 4) and 17.1 (group 5) microg I/kg]. Carry over (of supplemented iodine) into muscle/fat varied between 0.10 and 0.24%. The highest tested iodine dosage (5 mg I/kg diet) caused a 3.6-fold iodine concentration of the total body (calculated from the contents of the fractions), and a significantly increased thyroid weight compared to the group without supplementary iodine. Iodine supplementation increased iodine content in thyroid and bones significantly (P < 0.05) but not in innards/blood. On an average of the groups, the thyroid contained 80% of the body's iodine, innards/blood 14%, muscle/fat 5% and bones 1%. CONCLUSIONS: The iodine content of pork, and consequently its contribution to human iodine supply ( approximately 1%), is very low, even at high supplementation of feed. The total body iodine content (empty body) is determined by the iodine intake. Irrespective of the iodine dosage, the thyroid contains about 4/5 of the body iodine. Bones represent a very low iodine concentration, even at a strongly increased iodine intake. The increase of the thyroid weight as an adverse effect of iodine supplementation requires further research with high dietary iodine.

Nutritional assessment of genetically modified rapeseed synthesizing high amounts of mid-chain fatty acids including production responses of growing-finishing pigs.

The nutritive value of genetically modified myristic acid-rich rapeseed, in which a acyl-thioesterase gene inserted, was studied. Crude nutrients, amino acid and fatty acid profiles as well as mineral and glucosinolate contents were determined and compared with those of the non-transgenic parental cultivar. The concentration of crude nutrients, minerals and amino acids were found to be within the range of natural variance. The myristic and palmitic acid content increased from 0.1 - 11.4% and from 3.6-20%, respectively, at the expense of oleic acid, which decreased from 68.6-42.6% of total fatty acids. The glucosinolate contents increased from 12.4 micromol/g in the parental plant to 19 micromol/g DM in the GM-plant. Full-fat rapeseed of both cultivars was incorporated in pig diets at a level of 15%, and the digestibility and the production efficiency were tested under ad libitum feeding conditions with ten pigs each over the growing finishing period from 32-105 kg BW. The experimental diets did not show significant differences in digestibility and energetic feeding value. However, feed intake and weight gain decreased presumably due to the increasing glucosinolate intake associated with the feeding of transgenic rapeseed. The dietary fatty acids profile influenced the fatty acid profile of body fat. Myristic acid accumulated in back fat and intramuscular fat while the oleic acid content decreased. The increased glucosinolate intake affected the weight of thyroid glands and their iodine concentration.