The experiment was carried out on a mini farm of Holstein-Friesian cows with 30 animals, aged between 3 and 5 years and the zinc level in serum was measured. The analyses of the blood samples indicated a variation in the concentration of zinc in serum. In 11 out of 15 tested cows (73.33%) the zinc values in serum were below the physiological values for high-milking cows. In the experimental group different thickness of the keratin layer was detected in the teat canal. The statistical analysis showed a positive correlation between the concentration of zinc in cow serum and the thickness of teat canal keratin layer. This indicates that the cows with low values of zinc have thin keratin layer of the teat canal.
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