breeding region and season on the content of some trace elements and heavy metals in the hair of cows. Folia Biologica (Kraków) 62: 163-169. The aim of the research was to determine the effect of the season and the breeding region on the content of selected minerals (Zn, Cu, Mn, Fe, Pb, Cd) in the hair of dairy cows. The research material covered 114 Holstein-Friesian breed cows from three breeding centres in Poland, hereafter referred to as A, B and C. Breeding centre A is located in Opolskie province, breeding centre B in Podlaskie province and breeding centre C in Kujawsko-Pomorskie province.The cows were kept in freestanding cowsheds with den boxes. Animal nutrition involved the use of the TMR system, considering division into nutrition groups. Hair was sampled in summer and in the period of winter and spring from the side of the body, directly behind the coastal arch. The Zn, Cu, Mn, Fe analysis was performed with atomic absorption spectrometry. The Pb and Cd content was assayed with the use of the electrothermal atomic absorption spectrometry. The results demonstrated the effect of season and breeding region on the level of the minerals and heavy metals assayed in the hair of cows being in the period of drying-off. The hair sampled in winter from cows from C demonstrated a higher concentration of most elements except for Fe than in material derived in summer. Hair

The aim of the research was to analyze the effect of the season and the breeding region on the content of selected minerals (Ca, Mg, Na and K) in the hair of dairy cows. The research material was made up of 114 polish Holstein-Friesians breed cows from three breeding centres in Poland: Kombinat Rolny Sp. z o. o. -Kietrz (the opolskie province), Hodowla Zarodowa Zwierząt Sp. z o.o. -Knyszyn (the podlaskie province) and Ośrodek Hodowli Zarodowej Sp. z o.o. -Osięciny (the kujawskopomorskie province). The cows were kept in freestanding cowsheds with den boxes. The animal nutrition involved the use of the TMR system, considering the division into nutrition groups. The hair was sampled in summer and in the period of winter and spring from the side of the body, right behind the coastal arch. Determination of Ca, Mg, Na and K was performed by means of atomic absorption spectrophotometry (AAS). The study revealed seasonal variations in the content of mineral elements in the hair of dry cows and a region-dependent differentiation. The highest content of the quantity elements in question was found in the hair of the cows from Osięciny. The mean concentration of Ca, Mg, Na and K in the hair of cows from Osięciny was statistically significantly higher than in the hair collected in winter from the animals from Knyszyn and Kietrz. The lowest values of the determined elements were noted in the hair of cows bred in Knyszyn. The investigation of the correlation between the amounts of the elements, based on an analysis of all samples of hair, revealed a positive correlation between Na and K cations, as well as between Mg and Ca cations.