Abstract. The aim of the work was to determine the effect of the condition of the sows in high pregnancy, being expressed by fat reserves and body weight, and of lactation period on chemical composition and energy content as well as physical and cytological parameters of colostrum and milk of the sows. The studies were conducted with 100 sows (PLW × PL), classified into the groups according to backfat thickness: I – (P₂ + P₄)/2>20 mm and II – (P₂ + P₄)/2≤20 mm. The experiment was performed since 104th day of pregnancy till weaning of piglets after 21-day lactation. Fatness (points P₂ and P₄) and their changes during the periods: high pregnancy – parturition – weaning as well as physical and cytological parameters and colostrum and milk composition were examined.

Domination of fatness in highly pregnant sows from group I vs. II was maintained during parturition and weaning (P≤0.001). Any effect of the sow condition on colostrum and milk quality was not found. In case of lower fat reserves in sows (group II vs. I) only lower fat content in colostrum and its lower energy content (by 16.3 % and 4.9 %, respectively), was found. For the majority of parameters no significant differences between the two groups were found. Only the bodyweight at weaning in group II, despite smaller number of piglets in the litter, was found to be significantly lower.