Changes in fatty acid profile and iodine content in milk as influenced by the inclusion of extruded rapeseed cake in the diet of dairy cows

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). Percentages of milk fat and protein were higher in R than in S (P < 0.05). The total content of SFA and UFA was not affected by the treatment (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 contents of C18:2 and C18:3 isomers and metabolites in R were lower than in S (P < 0.05). The content of cis-9, trans-11 CLA and trans-10, cis-12 CLA was lower in R (0.71 and 0.016 g/100 g) compared to S (0.97 and 0.022 g/100 g, respectively, P < 0.05). The index of atherogenicity and peroxidisability in R was lower than in S (P < 0.05). The index of desaturation was not affected by the treatment (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 μg/l) in comparison with S (367.0 μg/l, P < 0.05) resulting in the lower daily iodine output in milk in R compared to S (4.4 and 9.2 mg/day, respectively, P < 0.05). Concentrations of T3 and T4 in blood plasma were not affected by the treatment (P > 0.05).