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

Simple Summary Zinc (Zn) is an essential trace mineral required for milk production and maintaining the optimal health of dairy cows. The current nutrient requirement models (e.g., NASEM (2021)) predict the dietary Zn requirement of dairy cows to be 60 mg/kg of dry matter (DM), based on the milk production and dry matter intake (DMI) of cows. North American farmers, however, supplement Zn at a higher rate of 76 mg/kg of DM, and a meta-analysis demonstrated that even higher Zn supplementation at 100 mg/kg of DM could improve udder health. In this study, increasing the dietary Zn supplementation from 76 to around 97 mg/kg of DM decreased the DMI by about 1.0 kg/d, but it improved the post-peak milk yield, which was associated with an increased milk protein yield and decreased somatic cell count in milk. Overall, the data highlight the possibility of improving the udder health and milk yield persistency by increasing the organic Zn supplementation well above the current recommendations. Because milk yield persistence and low somatic cell counts have critical implications for economic viability and animal well-being, Zn supplementation will directly affect the overall sustainability of dairy production.Abstract 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.