Abstract
The objective of the present study was to evaluate serum trace element and mineral levels in low- and high-productive dairy cows during feedlot and pasture periods. Serum trace element and mineral levels were assessed inductively-coupled plasma mass-spectrometry. The obtained data demonstrate that serum Ca, Mg, K, and Na levels increase significantly in the pasture period, and this increase is more evident in high-productive cows. In turn, circulating levels of B, Co, Cr, Fe, I, and Se levels were characterized by a decrease in the pasture period. Despite the lack of group differences in the feedlot period, serum B, Cr, and Fe levels in the pasture period were higher in high-productive cows. In turn, circulating Co and I concentrations in the low-productive cows exceeded those in high-productive animals. Finally, the levels of toxic trace elements in the pasture period were found to be higher in low-productive cows. Discriminant analysis demonstrated that the groups of cows with different milk productivity were clearly discriminated in the pasture but not feedlot period. In addition, multiple regression analysis revealed a significant inverse and positive association of serum Pb and Cr levels with daily milk yield. Taken together, the obtained data demonstrate that the differences in serum trace element and mineral levels between the low- and high-productive cows are more profound in the pasture period. More beneficial trace element and mineral profile in high-productive cows may hypothetically contribute to higher milk yield. However, further more detailed studies are required to elucidate the mechanisms of this association.