In 1968, thyroid glands were obtained from young dairy animals born and raised in the areas of various Agricultural Societies of Finland. Breed, sex and carcass weight were recorded for each case. The thyroids were weighed and preparations made for the histological examination. The relative proportions of epithelium (E %), colloid (C %) and stroma (S %), and the height of the epithelial cells (Eμ), were estimated with histometric methods, and the absolute amount of epithelial tissue in grams per gland (Eg) was calculated. The relative size of the follicles (FN) was also determined. The glands were classified, on the basis of prevailing histological characteristics, into activity groups indicated by numbers from 1 (low) to 6 (high). The glands in groups 5 and 6 were considered histologically as abnormal. The data included both Ayrshires (375 ♂ and 239 ♀) and Finncattle (276 ♂ and 234 ♀), and was characterized by the following mean and range values: carcass weight 66.6 kg (7—214), thyroid weight 12.95 g (2.1—130.0), E % 26.1 (14.4—88.2), C % 70.2 (4.1—85.1), S % 3.7 (0.9—14.6), Eμ 5.0 (2.2—22.5), Eg 3.77 (0.44—98.15), FN 21.9 (9.0—84.7), histological activity 3.0 (1—6). Data obtained from the Ayrshire herd of the Viik Experimental Farm was used as a control material for this study. The correlation study revealed that breed and sex had very little effect on the various thyroid characteristics. Carcass weight, on the other hand, correlated significantly with all other thyroid characteristics except the E %. In order to evaluate the geographic distribution of goitre the data was divided into 15 groups according to the Agricultural Society in whose area the animals were born and raised. Effect of carcass weight on the weight, Eg, and histological activity of the thyroid was first eliminated (e.g. by calculating the deviations from the respective control values) before the 15 groups were comparable with each other. Investigations revealed that the thyroid weight, Eg, and E % were raised and the percentage of histologically abnormal glands was high in the Agricultural Societies of the District of Nyland & Nyland’s Swedish, the District of Tavastland, East-Tavastland, the District of Mikkeli, and North-Karelia. On the other hand, hardly any or no signs of goitre were found in the Agricultural Societies of Satakunta, Tavastland-Satakunta, and Kuopio. Attention was also paid to the consumption of iodized mineral salt mixtures by cattle in the various Agricultural Societies. The extent of variation found in the consumption rate was not, however, large enough to explain satisfactorily the differences in the goitre incidence. Since the mean consumption rate in whole Finland in 1967 was only 1/3 of that of the control herd, it is concluded that the amounts of supplemental iodine in the cattle rations should be considerably increased.
