Influence of high levels of dietary zinc in milk performance and biochemistry of lactating cows
Twenty-four lactating dairy cows were fed either a) 0, b) 500, c) 1000, or d) 2000 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) 1279 ppm. The level of supplemental zinc did not significantly affect milk production; FCM 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 scrum alkaline phosphatase; or apparent animal health. The addition of the supplement zinc materially increased the zinc content of the milk. However, the higher levels had progressively less effect with the milk from cows given 1000 ppm supplemental zinc containing as much zinc as those fed 2000 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. The values were: a) 2.1, b) 3.2, c) 4.0, and d) 7.5 ppm. Thus, the zinc concentrations 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. 14 references, 2 tables.
- Research Organization:
- Univ. of Georgia, Athens, GA (United States)
- OSTI ID:
- 5145523
- Journal Information:
- J. Dairy Sci.; (United States), Vol. 48
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
MAMMARY GLANDS
BIOLOGICAL FUNCTIONS
ZINC
BIOLOGICAL EFFECTS
ALKALINE PHOSPHATASE
BLOOD CHEMISTRY
BLOOD PLASMA
CHEMICAL COMPOSITION
COWS
DOSE-RESPONSE RELATIONSHIPS
FEEDING
INGESTION
LACTATION
METABOLISM
MILK
ANIMALS
BIOLOGICAL MATERIALS
BLOOD
BODY
BODY FLUIDS
CATTLE
DOMESTIC ANIMALS
ELEMENTS
ENZYMES
ESTERASES
FOOD
FUNCTIONS
GLANDS
HYDROLASES
INTAKE
MAMMALS
MATERIALS
METALS
ORGANS
PHOSPHATASES
RUMINANTS
VERTEBRATES
560305* - Chemicals Metabolism & Toxicology- Vertebrates- (-1987)