The aim of the study was to evaluate the effect of extruded rapeseed cake in diets of dairy cows on changes in milk fatty acid profile and iodine content in milk and on the thyroid gland status. An experiment was carried out on four lactating Holstein cows divided into 2 groups - experimental (R) fed a diet based on extruded rapeseed cake and control (S) fed a diet based on extruded full-fat soya. The experiment was divided into 4 periods of 42 days (21 days of preliminary period and 21 days of experimental period). Samples of milk and blood were taken three times a week during the experimental period. DMI was not affected by the treatment (P > 0.05). Milk yield and 4% FCM were lower in R compared to S (P 0.05). However, the content of MUFA in R was higher (34.71 g/100 g) and the content of PUFA was lower (4.00 g/100 g) than in S (32.14 and 5.54 g/100 g, respectively (P 0.05). The mean daily intake of glucosinolates (Gls) in R was 50.14 mmol and resulted in a significant decrease in iodine concentration in milk in R (196.7 mu g/l) in comparison with S (367.0 mu g/l, P 0.05)
