The composition and quality of milk depend on various factors, among other things, on genetic and environmental conditions, physiological status of animals, and season of the year. The effect of season of the year is reflected by the seasonality of milk production (winter season: indoor feeding; summer season: pasture feeding). However, in recent years, the conditions of dairy farming have changed, i.e. cows are kept in cowsheds all year long and the pasture feeding has been replaced by a PMR feeding system. This could be linked with changes in milk composition, including changes in the profile of fatty acids. In order to verify this hypothesis, a research study has been undertaken and focused on the analysis of fat in milk from the summer and winter periods. The milk studied was provided by a large farm applying a PMR feeding system. The milk fat was extracted using a Röse-Gottlib method; the methyl esters of fatty acids in the fat extracted were prepared according to an IDF Standard method. The separation of methyl esters was performed by gas chromatography with the use of a gas chromatograph equipped with a flame ionization detector (FID). It was found that the fat from milk obtained in summer had more unsaturated fatty acids and the fat in milk from winter contained more saturated fatty acids. Those differences resulted from, primarily, the increased content of oleic, stearic, and polyunsaturated fatty acids, as well as from the decreased content of palmitic, myristic, and lauric acid in the summer period. Additionally, it was proved that despite the raising of cows in cowsheds, still, there were changes in the profile of fatty acids appearing characteristic for the summer and winter period.
cow’s milk, fatty acids, feeding season, summer season, and winter season, raising in cowshed