Influence of phytogenic substances with thyreostatic effects in combination with iodine on the thyroid hormones and somatomedin level in pigs.

Growing pigs were given 8% rape seed meal (RSM), which was offered without or with different iodine-supplements and further trace elements. RSM without I-supplementation reduced food intake and weight gains by more than 50%, thyroid weight increased by the factor 6, T4 declined below the detectable limit, T3 by two thirds and somatomedin activity by 50% compared to the control group (soy bean meal). In spite of supplementation with iodine and further trace elements the T3-level reached the level of the control group in no variant due to nutrient deficiency (reduced food intake) and the conversion-impeding effect of goitrogenic substances. The same is true for Sm-activity and weight gains, whereas the T4-level increased even above the level of control animals due to I-supplementation. There are significant correlations (correlation coefficients 0.77 and 0.64 resp.; p less than 0.001) between food intake and T3-concentration resp. and Sm-activity. This study demonstrate that the reduced growth in case of the intake of phytogenic substances with thyreostatic effects is directed by the diminished food consumption and the peripheral hypothyroid situation via decreased Sm-synthesis. The high content of thyreostatic substances in tissues of rape seed fed animals is a potential danger for the human consumer.