Evaluation of a novel, sensitive thyroid-stimulating hormone assay as a diagnostic test for thyroid disease in cats.

OBJECTIVE: Clinicians commonly use thyroid-stimulating hormone (TSH) concentrations to diagnose thyroid disorders in humans and dogs. In cats, canine TSH chemiluminescent immunoassays (CLIA) assays are commonly used to measure TSH, but these TSH-CLIAs cannot measure low TSH concentrations (< 0.03 ng/mL) and therefore cannot distinguish between low-normal concentrations and truly low TSH concentrations (characteristic of hyperthyroidism). Our aim was to evaluate a novel TSH assay based on bulk acoustic wave (BAW) technology that has lower functional sensitivity (0.008 ng/mL) than TSH-CLIAs. ANIMALS: 169 untreated hyperthyroid cats, 53 cats treated with radioiodine (131I), 12 cats with chronic kidney disease (CKD), and 78 clinically healthy cats. METHODS: Serum concentrations of T4, TSH-CLIA, and TSH-BAW were measured in all cats. Untreated hyperthyroid cats were divided into 4 severity groups (subclinical, mild, moderate, and severe), whereas 131I-treated cats were divided into euthyroid and hypothyroid groups. RESULTS: Test sensitivity, specificity, and positive predictive value for identifying hyperthyroidism were higher for TSH-BAW (90.5%, 98.9%, and 86.9%) than TSH-CLIA (79.9%, 76.7%, and 21.7%; P < .001). Test sensitivity for identifying 131I-induced hypothyroidism was only 45.5% for T4 versus 100.0% for both TSH-CLIA and TSH-BAW (P = .03), whereas TSH-BAW had a higher positive predictive value (100%) than did either TSH-CLIA (81.2%) or T4 (71.9%). CLINICAL RELEVANCE: Serum TSH-BAW alone or together with T4 is a highly sensitive and specific diagnostic test for evaluating feline hyperthyroidism and iatrogenic hypothyroidism. Finding low serum TSH-BAW concentrations is most useful for diagnosing subclinical and mild hyperthyroidism, in which serum T4 remains within or only slightly above the reference interval.

Diagnosis and management of thyroid disorders and thyroid hormone supplementation in adult horses and foals.

Equine thyroid disorders pose a diagnostic challenge in clinical practice because of the effects of nonthyroidal factors on the hypothalamic-pituitary-thyroid axis, and the horse's ability to tolerate wide fluctuations in thyroid hormone concentrations and survive without a thyroid gland. While benign thyroid tumours are common in older horses, other disorders like primary hypothyroidism or hyperthyroidism in adult horses and congenital hypothyroidism in foals are rare. There is a common misunderstanding regarding hypothyroidism in adult horses, especially when associated with the clinical profile of obesity, lethargy, and poor performance observed in dogs and humans. Low blood thyroid hormone concentrations are often detected in horses as a secondary response to metabolic and disease states, including with the nonthyroidal illness syndrome; however, it is important to note that low thyroid hormone concentrations in these cases do not necessarily indicate hypothyroidism. Assessing equine thyroid function involves measuring thyroid hormone concentrations, including total and free fractions of thyroxine (T4) and triiodothyronine (T3); however, interpreting these results can be challenging due to the pulsatile secretion of thyroid hormones and the many factors that can affect their concentrations. Dynamic testing, such as the thyrotropin-releasing hormone stimulation test, can help assess the thyroid gland response to stimulation. Although true hypothyroidism is extremely rare, thyroid hormone supplementation is commonly used in equine practice to help manage obesity and poor performance. This review focuses on thyroid gland pathophysiology in adult horses and foals, interpretation of blood thyroid hormone concentrations, and evaluation of horses with thyroid disorders. It also discusses the use of T4 supplementation in equine practice.

Biological variation of serum thyrotropin and thyroid hormones concentrations determined at 8-week intervals for 1 year in clinically healthy cats.

BACKGROUND: Cats commonly develop thyroid disease but little is known about the long-term biological variability of serum thyroid hormone and thyrotropin (thyroid-stimulating hormone; TSH) concentrations. OBJECTIVES: We aimed to determine the long-term biological variation of thyroid hormones and TSH in clinically healthy cats. METHODS: A prospective, observational study was carried out. Serum samples for analysis of total thyroxine (T4, by radioimmunoassay [RIA] and homogenous enzyme immunoassay [EIA]), triiodothyronine (T3 ), free T4 (by dialysis), and TSH were obtained every 8 weeks for 1 year from 15 healthy cats, then frozen until single-batch analysis. Coefficients of variation (CV) within individual cats ( CV I ) and among individual cats ( CV G ), as well as the variation between duplicates (ie, analytical variation [ CV A ]) were determined with restricted maximum likelihood estimation. The indices of individuality (IoI) and reference change values (RCVs) for each hormone were calculated. RESULTS: Some thyroid hormones showed similar (total T4 by EIA) or greater (TSH) interindividual relative to intraindividual variation resulting in intermediate to high IoI, consistent with previous studies evaluating the biological variation of these hormones weekly for 5-6 weeks. By contrast, total T4 (by RIA) and free T4 had a low IoI. Total T3 had a high ratio of CV A to CV I ; therefore, interindividual variation could not be distinguished from analytical variation. No seasonal variability in the hormones could be demonstrated. CONCLUSIONS: Clinicians might improve the diagnosis of feline thyroid disease by establishing baseline concentrations for analytes with intermediate-high IoI (total T4, TSH) for individual cats and applying RCVs to subsequent measurements.

Morphometry, topography and arterial supply of the thyroid gland in brazilian shorthair cat

Thyroid gland diseases are the most common endocrinopathies in feline practice. Diagnosis and surgical treatment must base on solid anatomical knowledge about the gland size, localization, and blood supply. However, some textbooks provide a general anatomical description of the thyroid gland of domestic carnivores. Thus, specific details of the feline gland are missing. The present study aimed to investigate the dimensions, topography, and arterial supply of the thyroid gland in Brazilian shorthair cats and, therefore, provide additional data to diagnose and treat feline thyroid diseases. Thirty Brazilian shorthair cats formalin-fixed cadavers (15 male and 15 female) were injected with red-stained latex solution by a canula in the thoracic aorta. The necropsy unit of the Rural Federal University of Rio de Janeiro donated the specimens. The study included only adult animals with no history of thyroid disease. After the fixation period, the cadavers were dissected to investigate the measurements (length, width at cranial and caudal poles, and thickness), topography, and in situ arterial supply of the thyroid lobes. The mean measurements of the length, cranial pole width, caudal pole width, and thickness in the right lobe were 19.39 ± 3.10 mm, 5.36 ± 1.40 mm, 3.67 ± 0.93 mm, and 1.30 ± 0.29 mm, respectively; and 20.29 ± 3.35 mm, 4.85 ± 1.58 mm, 3.88 ± 0.91 mm, 1.64 ± 0.65 mm in the left lobe, respectively. There were no statistical differences (P > 0.05) in the comparison of the measures between sexes or antimers (sides). Pearson's linear correlation detected a positive, moderate (r = 0.55), and significant (P < 0.05) correlation between the right and left lobe lengths. In 70% of the cats, both left and right lobes had the cranial poles located at the same level. Typically, the lobes extended between the first to the eighth tracheal ring. However, the cranial pole of some lobes located as cranially as the cricoid cartilage level, and the caudal pole as caudally as the 12th tracheal ring. Fifty-six percent of the cats had a ventrally located isthmus. In all the sampling, one single thyroid artery emerged as a branch of the common carotid artery and provided branches directly to the thyroid lobe, isthmus and the adjacent muscles and esophagus. Besides establishing average dimensions of normal thyroid lobes in Brazilian shorthair cats, this study detected no significant difference between the average measurements of right and left lobes. Also, a positive linear correlation between the length and width of the right and left lobes became evident. Therefore, the practitioner must consider suspicious any length asymmetry between right and left thyroid lobes until further endocrine test proves otherwise. Most of the cats had the right and left thyroid lobe positioned at the same transversal level; however, positional asymmetries are not uncommon. Unlike dogs, Brazilian shorthair cats have only a single artery to supply each lobe: the thyroid artery. In a feline thyroidectomy, the surgeon must avoid blindly ligating the thyroid artery since this vessel also provided numerous branches to adjacent muscles and esophagus. In a bilateral thyroidectomy, the ventral region between lobes should be thoroughly inspected for the common presence of an isthmus. Sometimes, the surgeon may need to extend the incision caudally beyond the 12th tracheal ring level to visualize the gland tissue entirely.(AU)

Updates on Thyroid Disease in Rabbits and Guinea Pigs.

Hyperthyroidism seems to be a rare, but likely underdiagnosed disease of guinea pigs (Cavia porcellus) and rabbits (Oryctolagus cuniculus). Diagnosis is confounded by nonspecific clinical signs, lack of validated assays, and species-specific reference intervals. With increasing English-language publications on the topic, naturally occurring thyroid disease is likely to be increasingly diagnosed in exotic small mammals. The most consistently observed clinical signs include weight loss with or without a change in appetite and a palpable cervical mass. Diagnosis is supported by elevated blood thyroxine concentrations. Treatment may include thyreostatic agents, radioactive iodine, or surgical thyroidectomy.

The organophosphate pesticide -OP- malathion inducing thyroidal disruptions and failures in the metamorphosis of the Senegalese sole, Solea senegalensis.

BACKGROUND: Organophosphate pesticides-OP-, like malathion, can alter the normal functioning of neuro-endocrine systems (e.g., hypothalamus-pituitary-thyroid-HPT- axis), and to interfere on the thyroidal homeostasis. Through direct interactions with thyroid receptors, an/or indirectly via up-stream signalling pathways, from the HPT axis (i.e., negative feedback regulation), malathion possess the ability to affect integrity of thyroidal follicular tissue, and it can also block or delay its hormonal functioning. This insecticide can alter the majority of the ontogenetic processes, inducing several deformities, and also provoking decreases in the growth and survival patterns. The present study has been performed to determine the sublethal effects of malathion during the first month of life of the Senegalese sole, Solea senegalensis, and it is mainly focused on the metamorphosis phase. Different transcript expression levels (i.e. thyroid receptors, matrix and bone -Gla-proteins) and immunohistochemical patterns (i.e. thyroid hormones, osteocalcin, cell proliferation) have been analysed during the most critical phases of the flatfish metamorphosis, that is, through differentiation of thyroid system and skeletal development, migration of the eye, and further adaptation to benthic behaviours. RESULTS: In early life stages of the Senegalese sole, the exposure to the highest concentration of malathion (6.25 µg/L) affected to the growth patterns, showing the exposed individuals, a reduction around 60 and 92% of the total length and the dry weigth, respectively. In paralell, a significant reduction of the thyroid follicles (i.e., size and number) it was also been recorded, in a dose-dependent way. Abnormal phenotypes induced in the exposed larvae, did not complete the process of metamorphosis, and displayed several morphological abnormalities and developmental disorders, which were mainly associated with the eye migration process, and with thyroidal and skeletal disorders (i.e., transcriptional and protein changes of thyroid hormones and receptors, and of matrix and bone Gla proteins distribution), that conduced to an inadequate adaptation to the benthic life. CONCLUSIONS: In the Senegalese sole, the majority of the ontogenetic alterations induced by the exposure to malathion were mainly associated to the metamorphosis period, which is a thyroid-driven proccess. In fact, most crucial and transitional ontogenic events, appeared notably disturbed, for e.g., thyroid gland differentiation and functioning, migration of eye, skeletal development and benthonic behaviors.

Evaluation of an automated enzyme-linked fluorescent assay for thyroxine measurement in cat and dog sera.

Measurement of total thyroxine (T4) is the first testing step in the work-up of thyroid disease in small animals. We evaluated an enzyme-linked fluorescent assay (ELFA) as an in-house method to measure T4 in cats and dogs. We compared the T4 concentration in sera of 122 cats and 176 dogs measured by the ELFA with an enzyme immunoassay (EIA) to assess the concordance of the 2 methods. Bias of the ELFA in cats was -11.4% and in dogs 1.4%. Using Bland-Altman plots, limits of agreement were -81.5 to 58.7% in cats and -71.4 to 74.4% in dogs. Imprecision was calculated for both methods. Intra- and interassay coefficients of variation (CVs) of the ELFA in feline sera were 0.7 and 3.4% and of the EIA 7.6 and 15.7%, respectively. Intra- and interassay CVs of both ELFA and EIA in canine sera were <9.5%. Reference intervals for the ELFA method were established and were 13.3-49.5 nmol/L for cats and 10.1-42.9 nmol/L for dogs. Accuracy of the EIA and ELFA was scored by assessing if the measured T4 value would identify the expected T4 range (low, normal, or elevated) of patients, based on history, clinical presentation, other diagnostic means, and response to therapy. This was possible for 75 cats and 50 dogs. Both methods yielded acceptable results, but the EIA was more accurate compared to the ELFA (percentage of true-positives in cats and dogs: EIA: 97% and 100%; ELFA: 92% and 94%).

Prevalence of incidental thyroid nodules in ultrasound studies of dogs with hypercalcemia (2008-2013).

Ultrasound is commonly used to evaluate the cervical region in dogs with hypercalcemia due to suspected hyperparathyroidism. Incidental thyroid nodules may be detected during these studies, however little information has been published to guide clinical decision-making when this occurs. The purpose of this cross-sectional study was to determine the prevalence of incidental thyroid nodules in hypercalcemic dogs undergoing cervical ultrasound at our hospital during the period of 2008-2013. Dogs with a palpable neck mass were excluded. Cervical ultrasound images for each dog were retrieved and reviewed by a board certified veterinary radiologist who was unaware of patient outcome. Presence, number, and dimensions of thyroid nodules were recorded. Results of thyroid nodule aspirate, biopsy or necropsy were recorded from medical records when available. Ninety-one dogs met inclusion criteria. Of these, 14/91 (15%) dogs had at least one thyroid nodule. Mean (± standard deviation) thyroid gland nodule length, width, and height were 1.51 ± 0.74, 0.96 ± 0.73, and 0.75 ± 0.36 cm, respectively. A histologic diagnosis was available for the incidental thyroid lesions in eight dogs, including one dog with two nodules. Confirmed diagnoses for these nodules were thyroid cyst (3/9, 33%), thyroid adenoma (3/9, 33%), thyroid adenocarcinoma (2/9, 22%) and nodular hyperplasia (1/9, 11%). Findings indicated that incidental thyroid nodules may be present in hypercalcemic dogs with no palpable neck mass and no clinical signs of thyroid disease. Some of these nodules may be malignant and therefore a recommendation for cytology or biopsy may be justified.

Thyroid function and dysfunction in term and premature equine neonates.

BACKGROUND: This study was performed to compare thyroid function of premature foals to term foals. HYPOTHESIS: Premature foals are more markedly hypothyroxinemic than expected for their severity of illness alone. ANIMALS: Twenty clinically normal term foals; 28 sick, hospitalized term foals; 24 sick, hospitalized premature foals. METHODS: Thyroid hormones (TH) and thyrotropin (TSH) were measured, both at rest and in response to thyrotropin-releasing hormone (TRH), in the 3 groups of foals. Clinical and clinicopathologic data were recorded. RESULTS: Normal foals had high TH at birth, which decreased over the first month into the normal reference range for adult horses. TSH was within the normal adult reference range soon after birth, and did not change over time. At 24-36 hours of age, triiodothyronine (T3) was significantly lower in both premature and term hospitalized foals compared to normal foals; premature foals were not different from term hospitalized foals. Thyroxine (T4) was not different between normal and term hospitalized foals, but was significantly lower than in premature foals of both of these groups. TSH was not different among the 3 groups. TRH stimulation tests identified significant differences in T4 among all 3 groups of foals, whereas T3 was similar in premature and term hospitalized foals and different from normal foals. TSH response to TRH was significantly higher in premature foals compared to normal foals. CONCLUSIONS AND CLINICAL IMPORTANCE: The hypothalamic-pituitary-thyroid axis is different in foals compared to adult horses. Sick foals exhibit nonthyroidal illness syndrome. Premature foals are more markedly hypothyroxinemic than can be accounted for by their severity of illness alone.

Thyroid diseases in rodent species.

There are an abundance of studies of thyroid disease in rodents in a laboratory setting; however, research is limited in pet rodent populations. Validated reference intervals for thyroid testing are scarce, making interpretation of blood work difficult. Hyperthyroidism and hypothyroidism have been reported in multiple rodent species, with the most data available for guinea pigs. Thyroid neoplasia has been reported in the most common rodent species, although often as an incidental finding at necropsy. Further research is needed to determine frequencies of disease, methods of diagnosing, and treatment options with the best efficacy.

Thyroid disorders in the geriatric veterinary patient.

The effects of age, concurrent illness, and administered medications complicate diagnosis of thyroid dysfunction in geriatric patients. Interpretation of thyroid hormone testing should take these factors into account. The most common thyroid disorder in dogs is acquired hypothyroidism. Therapeutic monitoring should be utilized for monitoring treatment of canine hypothyroidism. The most common thyroid disorder in cats is benign hyperthyroidism. Diagnosis is most often complicated by the presence of concurrent illness. Treatment should be individualized based on individual case characteristics and presence of concurrent illness. Some older cats have a palpable goiter months to years before development of clinical signs of hyperthyroidism.

Disorders of the equine thyroid gland.

Regulatory control of the thyroid gland in horses is similar to other species. Clinical signs of hypothyroidism in adult horses are minimal. Several drugs and physiologic and pathophysiological states can cause circulating thyroid hormone concentrations to be low without actual pathology of the thyroid gland. Thus, nonthyroidal factors must be ruled out before a diagnosis of hypothyroidism can be made. Thyroid hormone supplementation seems to be well tolerated, even in euthyroid horses. Neonatal foals have very high circulating thyroid hormone concentrations, and deficiencies result in significant clinical signs. Unlike in adults, two syndromes of hypothyroidism are well described in foals.

Advanced diagnostic approaches and current management of thyroid pathologies in Guinea pigs.

The authors have encountered multiple clinical cases of clinical hyperthyroidism in the guinea pig, which responded positively to clinical treatment. Hyperactive thyroids in the guinea pig appear to exist causing typical clinical signs. An early accurate diagnosis of this pathologic state is important in the clinical setting. One of the authors has encountered a few clinical cases of hypothyroidism in guinea pigs. Hypothyroidism appears to be a rare condition and has been described anecdotally in the German literature. Because of the rarity of hypothyroidism, the text focuses mainly on the guinea pig as a hyperthyroid case. A short description of the clinical presentation of the hypothyroid animal is included at the end of the text.

Comparison of histological features, and description of histopathological lesions in thyroid glands from three species of free-ranging sharks from the northwestern Atlantic, the blue shark, Prionace glauca (L.), the shortfin mako, Isurus oxyrhinchus Rafinesque, and the thresher, Alopias vulpinus (Bonnaterre).

Abstract Histomorphological features of piscine thyroids are widely accepted and frequently used as bioindicators of environmental pollution. This despite the fact that there is marked variation in thyroid morphology resulting from numerous pathological and physiological conditions. Our hypothesis was that there will be variations in histological features in thyroids collected from different shark species during the summer season in the northwestern Atlantic. To test our hypothesis, we examined histological features encountered in grossly normal thyroids from three species of sharks, the shortfin mako, Isurus oxyrhinchus, thresher, Alopias vulpinus and blue sharks, Prionace glauca. In addition, microscopic lesions from these thyroids were described. Ninety-four sharks were collected in summer 2001, 2002 and 2004. Routine, haematoxylin and eosin-stained paraffin-embedded sections were studied by light microscopy. We found inter-species but not intra-species variation in histological patterns of thyroids, which were distinct enough to allow 'blind' assignment of a thyroid to the specific species. The most common lesions encountered were lymphofollicular hyperplasia and chronic thyroiditis. In addition, one case each of intravascular larval nematodes and a myxosporean infection was found. Our results provide the first data on species-specific morphology of thyroids collected during summer months from sharks. The results indicate that familiarity with normal thyroid morphology is crucial before using shark thyroids in biomonitoring of environmental contamination or interpreting data from this gland in shark-health studies.

Influence of isoflurane general anesthesia or anesthesia and surgery on thyroid function tests in dogs.

BACKGROUND: Anesthesia and surgery affect thyroid function tests in humans but have not been studied in dogs. HYPOTHESIS: Anesthesia and anesthesia with surgery will affect thyroid function tests in dogs. ANIMALS: Fifteen euthyroid dogs. METHODS: Prospective, controlled, interventional study. Dogs were assigned to one of 3 groups: control, general anesthesia, and general anesthesia plus abdominal exploratory surgery. Dogs in the anesthesia and surgery groups were premedicated with acepromazine and morphine, induced with propofol, and maintained on isoflurane. Samples for measurement of serum thyroxine (T4), free T4 (fT4) by equilibrium dialysis, triiodothyronine (T3), reverse T3 (rT3), and thyroid-stimulating hormone concentrations were collected from each dog immediately before premedication, at multiple times during anesthesia, surgery, 4, 8, 12, 24, 36, and 48 hours after anesthesia, once daily for an additional 5 days, and once 14 days after anesthesia. Sampling was performed at identical times in the control group. RESULTS: Serum T4 decreased significantly from baseline in the surgery and anesthesia groups compared with the control group at 0.33 (P= 0.043) and 1 hour (P= 0.018), and 2 (P= 0.031) and 4 hours (P= 0.037), respectively, then increased significantly in the surgery group compared with the control group at 24 hours (P= 0.005). Serum T3 decreased significantly from baseline in the anesthesia group compared with the control group at 1 hour (P= 0.034). Serum rT3 increased significantly from baseline in the surgery group compared with the control and anesthesia groups at 8 (P= 0.026) and 24 hours (P= 0.0001) and anesthesia group at 8, 12, 24, and 36 hours (P= 0.004, P= 0.016, P= 0.004, and P= 0.014, respectively). Serum fT4 increased significantly from baseline in the surgery group compared to the control at 24 hours (P= 0.006) and at day 7 (P= 0.037) and anesthesia group at 48 hours (P= 0.023). CONCLUSIONS AND CLINICAL IMPORTANCE: Surgery and anesthesia have a significant effect on thyroid function tests in dogs.

Thyroid function in anhidrotic horses.

BACKGROUND: This study was performed to determine whether anhidrotic horses have altered thyroid function compared with horses that sweat normally. HYPOTHESIS: Anhidrotic horses have normal thyroid function. ANIMALS: Ten client-owned horses with clinical signs of anhidrosis were paired with 10 horses living in the same environment that had normal sweat production. METHODS: Horses were diagnosed as having normal sweat production or being anhidrotic based on responses to intradermal injections of terbutaline and physiologic responses to lunging exercise. Control horses were selected from the same environment and matched as closely as possible to anhidrotic horses in terms of age, sex, breed, and athletic condition. Thyrotropin-releasing hormone (TRH) stimulation tests were performed in both horses at the same time, once in the summer or fall, and once again in winter. RESULTS: Anhidrotic horses produced less sweat in response to intradermal injections of terbutaline and exercise than did control horses. They also had greater increases in body temperature and respiratory rate in response to exercise. Resting concentrations of thyroid hormones and thyroid-stimulating hormone (TSH) were not different between anhidrotic and control horses. Thyroid hormone responses to TRH also were not different between the 2 groups of horses. However, anhidrotic horses had a significantly different TSH response to TRH compared with control horses, particularly in the winter. CONCLUSIONS AND CLINICAL IMPORTANCE: The biologic relevance of the altered TSH response to TRH in anhidrotic horses is uncertain, considering that TSH concentrations remained within previously reported normal ranges and thyroid hormone responses were not different between anhidrotic and control horses.

The effect of chemically and hydrothermally treated rapeseed on the performance and thyroid parameters of layers.

A feeding trial with brown laying hens was carried out in order to examine the effects of chemical and hydrothermal treatment of rapeseeds on the performance and thyroid parameters of birds during a long-term experiment. Untreated and treated rapeseeds were included in layer diets at a level of 7.5, 15.0, 22.5 and 30.0%, and the results obtained were compared with a control group fed a diet containing no rapeseed. Rapeseed treatment involved a combination of chemical and hydrothermal processing with subsequent expansion and drying. This treatment decreased sinapine content, from 6152 mg rapeseed/kg to less than 50 mg/kg, and glucosinolate concentration, from 13.8 mmol per kg to 1.4 mmol per kg (basis - 91% dry matter). The inclusion of 22.5% and 30.0% of both untreated and treated rapeseeds significantly impaired egg-laying rate and feed conversion. Egg weight was significantly affected by rapeseed feeding, with a significant decline at the 30.0% vs. the 7.5% rapeseed level. Rapeseed inclusion in the diet had a negative influence on weight gain. An increase in the dietary levels of untreated rapeseeds caused a greater decrease in egg mass, hen weight and feed conversion ratio, compared with the respective levels of treated rapeseeds. Untreated rapeseeds at the lowest level of 7.5% in the diet caused an increase in thyroid weight, epithelial cell height and changes in other histomorphometric thyroid parameters, as well as a decrease in the serum concentrations of thyroid hormones. Treated rapeseeds at a dietary level of 22.5% evoked a dose response, which shows that the chemical and hydrothermal treatment of rapeseed considerably reduced the anti-thyroid effects.