The research involved 80 cows being in 2 physiological states: near the end of lactation (approximately 2 months before delivery) (N=40), and one month after calving. In plasma was established MDA level (malonylodialdehyde) and in milk SCC (Somatic Cells Count). The MDA level in plasma in groups of calved and non-calved cows remained at a similar level. It was found that a statistically signifi cant MDA level (p≤0,05) was present in milk from non-calved cows – with somatic cells count below 400,000 per ml during test milking, as compared to cows producing milk with somatic cells count of over 400,000 per ml.