Effects of Elevating Zinc Supplementation on the Health and Production Parameters of High-Producing Dairy Cows.

This study's objective was to determine the effects of increasing the dietary added zinc ( Zn ) on the milk production, milk somatic cell count ( SCC ), and immunoglobulin and antioxidant marker concentrations in the blood of dairy cows. Twelve Holstein cows (67 ± 2.5 days in milk) were assigned randomly to (1) a diet containing Zn-methionine at 76 mg/kg of DM ( CTL ) or (2) CTL top-dressed with about 21 mg/kg of DM extra Zn-methionine ( +Zn ) for 70 d. The concentrations of reduced ( GSH ) and oxidized ( GSSG ) glutathione, malondialdehyde ( MDA ), catalase ( CAT ), superoxide dismutase ( SOD ), and immunoglobulins in the blood were measured on d 0, 35, and 70. Compared to CTL, +Zn decreased the dry matter intake ( DMI ) throughout the trial and the milk yield ( MY ) during the first phase of feeding (0-35 d). It, however, increased the milk yield during the last phase (36-70 d). The +Zn tended to have lower and greater milk protein yields than CTL during the first and last feeding phases, respectively. The +Zn tended to decrease the SCC and was associated with lower plasma GSH: GSSG and lower serum SOD concentrations relative to CTL. The +Zn did not affect the immunoglobulins, MDA, or CAT. Despite the early DMI and MY reduction, the prolonged Zn-methionine supplementation at about 100 mg/kg of DM improved the milk yield, possibly as a result of the improved udder health of dairy cows.