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Influence of High Levels of Dietary Zinc on Zinc in Milk, Performance and Biochemistry of Lactating Cows¹

Dairy Science Department

H. F. Perkins

Agronomy Department, University of Georgia, Athena

ABSTRACT

Twenty-four lactating dairy 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 Bermudagrass and Sudan grass silages were fed ad libitum as the only source of forage and constituted 43% of dry matter intake. Average zinc contents of the total dry matter 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; FCM production; fat, SXF, 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.

The addition of the supplemental zinc materially increased the zinc content of the milk. However, the higher levels had progressively less effect with the milk from cows given 1,000 ppm supplemental zinc containing as much zinc as those fed 2,000 ppm. The average ppm of zinc in the milk of the four groups were: a) 4.2, b) 6.7, c) 8.0, and d) 8.4. Recoveries of zinc in the milk as percentages of dietary zinc were: a) 12.5, b) 2.2, c) 1.6, and d) 0.8 for those fed the four levels of zinc.

The blood plasma zinc concentration increased with increasing levels of supplemental zinc. These values were: a) 2.1, b) 3.2, c) 4.0, and d) 7.5 ppm. Thus, the zinc concentration increased at a much more rapid rate in plasma than in milk. This suggests that the udder is discriminating against zinc at the higher dietary and blood levels.

¹ Journal paper No. 388 of the College Experiment Station, University of Georgia. Supported in part by PHS research grant No. AM 07367-01 NTN from the National Institute of Arthritis and Metabolic Diseases, Public Health Service.