Effect of zinc methionine or zinc sulfate supplementation on milk production and composition of milk in lactating dairy cows.

Eighteen lactating dairy cows were used to compare the effects of organic and inorganic Zn supplements on milk production and chemical composition of milk. Animals received three diets in a randomized block design: basal diet with no supplemental Zn (control, 42 mg Zn/kg), basal diet plus 500 mg Zn/kg of dry matter (DM) as zinc sulfate monohydrate (ZnS) and basal diet plus 500 mg Zn/kg of DM as zinc methionine (ZnM). Results showed that milk and fat-corrected milk yield in dairy cows were not significantly affected by Zn source although a numerical increase was observed. The percentages of protein, lactose, fat, solid nonfat, total solid, and density of milk were not significantly different between treatments. However, dairy cows that received ZnM tended to produce more milk and fat-corrected milk with a lower somatic cell count as compared to controls. The zinc concentration in milk in the ZnM and ZnS groups was higher (P < 0.05) than in milk from the control group, but there were no significant differences between ZnS and ZnM groups.