Concentration of trace elements in raw milk depending on the lactation period and age of cows

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Concentrations of iron, zinc, manganese and copper in milk from cows of Polish Holstein – Friesian Black-White breed kept on five farms located in the southern Podlasie region in Poland were determined and analysed depending on the lactation period and age of cows. Milk samples were taken separately from each cow, 18 samples from one farm. A total of 90 milk samples were taken. Cows were in three age classes (lactation number): 1, 2-3 and >3, and four lactation periods (duration): ): ≤ 100, 101–200, 201–305 and > 305 days). The concentration of trace elements in milk was determined using atomic absorption spectrometry method. Average concentrations of the elements in 1 kg of fresh milk were the following: iron 173 ± 84 µg, zinc 3.6 ± 0.9 mg, manganese 27 ± 17 µg and copper 40 ± 23 µg. A relation between the age of cows and the concentrations of iron was observed. The lowest contents of iron (145 ± 72 µg·kg-1) were observed in the milk from the youngest cows in their first lactation, whereas the highest contents (217 ± 70 µg·kg-1) were observed in the milk from the oldest cows above the third lactation. No relation between the age of cows and the concentrations of zinc, manganese and copper in milk was observed. Similarly, no significant differences between the contents of these elements in different lactation periods were observed. Study on factors influencing the concentrations of trace elements in cow milk were undertaken because researches on the subject are not numerous.