Effect of zinc sources on milk yield, milk composition and plasma concentration of metabolites in dairy cows
This study was conducted to evaluate the effects of different sources of zinc (Zn) on feed intake, milk yield, milk composition, and blood metabolites. Twenty-four dairy cows were randomly allocated to one of four treatments in a randomized complete block design. The treatments consisted of i) control diet (no zinc supplementation), ii) zinc oxide (ZnO), iii) zinc glycine (ZnGly), and iv) zinc nano (ZnN). The Zn sources were added to provide 60 mg of supplemental Zn per kg diet. There were no differences in dry matter intake, milk yield, bodyweight, and body condition score of the cows between treatments. Zinc supplementation in the form of ZnN and ZnGly decreased somatic cell count compared with the other treatments. The superoxide dismutase and plasma Zn concentrations in the cows provided ZnGly and ZnN were greater than those in the ZnO and control groups. No difference was detected between groups in biochemical and haematological parameters, except that blood urea nitrogen concentrations of cows supplemented with ZnGly and ZnN were less than for the ZnO supplemented and control cows. The results showed that nano and organic Zn sources in the diet of dairy cows were more suitable than inorganic Zn as supplements for dairy cows.
Keywords: milk composition, milk production, metabolism, somatic cell count