Iron, cooper and zinc concentrations in blood plasma during lactation and the dry period in Holstein cows

The effect of the different phases of lactation and the dry period on the it-on, copper and zinc metabolism was studied prospectively in Holstein-Friesian cows. The study involved 60 Holstein cows in the second and third lactation and during the dry period. The cows were held in a free stall housing system with an enclosure. The cows were fed according to the phase of the production cycle. The blood samples were taken through jugular vein puncture, with lithium heparinate as the anticoagulant. The production cycle stage formed the basis of the four experimental groups. The first group comprised cows between the 5(th) to 45(th) day of lactation, the second group cows between the 46(th) to 90(th) lactation day of lactation, the third group cows from the 91(st) lactation day to the end of the lactation and the fourth group cows in their dry period. The blood plasma was centrifuged from the blood samples. Iron, copper, and zinc concentrations were determined by spectrophotometry. Fluctuations in the iron and copper concentrations in the blood plasma were observed during the research period but no statistically significant differences were observed. A significant rise in zinc concentration was observed during the second and third period of lactation and during the dry period in comparison with the first period of lactation (P < 0.05). The conclusion from the results of the study was that the homeostatic mechanism is well developed to maintain constant concentrations of it-on and copper in blood. The rise in the zinc concentration should be related to the importance of zinc in the development of the fetus together with the concentration of plasma albumins.