Influence of High Levels of Dietary Zinc on Zinc in Milk, Performance and Biochemistry of Lactating Cows

Twenty-four lactating dai D-cows were fed either a) 0, b) 500, e) 1,000, or d) 2,000 ppm of supplemental zinc (as ZnO) in the concentrate portion of the diet for 6 wk. Coastal Bernmdagrass and Sudan grass silages were fed ad libitum as the only source of forage and con.-tituted 43% of drs" matter intake. Average zinc contents of the total dry matWr of the four groups were: a) 44, b) 372, c) 692, and d) 1,279 ppm. The level of supplemental zinc did not significantly affect milk production; ]?C~[ production; fat, SNF, protein, or magnesium content of milk; voluntary forage dry matter intake; body weight changes; blood hemoglobin; packed cell volume; blood serum lactic dehydrogenase; blood serum alkaline phosphatase; or apparent animal health.