LEVELS OF THYROID AND THYROTROPHIC HORMONES IN THE BLOOD OF FRIESIAN COWS AT VARIOUS REPRODUCTIVE STAGES

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Abstract
Thyroid and thyro-trophic hormone levels in the blood of Friesian cows were determined during the oestrous cycle, at different months of pregnancy and 10 days after parturition. During the oestrous cycle there was an increase in the thyroid hormone level at oestrus accompanied by a decrease in the level of thyroid-stimulating hormone. The thyroid hormone content of blood was low during dioestrus while the thyrotrophic hormone was high. No variation in thyroid hormone level was noticed during pregnancy, except for an increase during the 9th month. The level of thyrotrophic hormone was maintained at a comparatively high level during the first 4 months of pregnancy. After parturition the level of thyroid hormone was similar to that observed during dioestrus, while there was an increase in the level of thyrotrophic hormone.