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The trace element zinc plays an important role in many metabolic functions.
In this study the relation between zinc concentration and different parameters of health and fertility in dairy cows was investigated. Different influence factors on the zinc concentration were statistically analyzed. Additionally the different samples (serum, plasma, whole-blood, urine, hair and liver tissue) were tested on their functionality to determine the zinc concentration and their characteristics to reflect the zinc status in dairy cows. Reference values for the different samples were established.
The analyzed data were accumulated between 1995 and 2002 by the department of herd-health of the Clinic for Ruminants and Swine of the Free University of Berlin.
The zinc concentration was statistically analyzed and reference values were determined for the different samples. Correlation analyses and regression analyses were used to identify physiologic and pathologic effects on zinc status.
All the samples investigated in this study reflect the zinc status but differ in their reaction speed and reaction intensity during deviation from optimum supply. Serum and plasma can be classified as fast reacting media where as whole-blood reflects the medium-term supply. Liver tissue and hair are very slow reacting media and can be used as long-term indicators. Urine can be used to evaluate dietary zinc supplementation because the renal elimination of zinc seems to be activated in times of zinc oversupply.
Time relative to calving has a significant effect on zinc concentration in all samples. Especially fresh cows (first week post partum) exhibit explicitly reduced zinc concentrations in serum and plasma. This dynamic is also reflected in whole-blood, liver and hair but due to their reaction speed a few weeks later. The reproductive performance of dairy cows is influenced by the zinc status. Cows with higher zinc levels in serum have shorter calving intervals and decreased days open with a reduced insemination index.
An existing correlation between zinc supply and somatic cell count as a parameter of udder health was identified. Cows with lower zinc levels in serum have higher somatic cell counts. In summary zinc plays a significant role in maintaining health of dairy cows.
The different samples can be used according to their characteristics to evaluate the zinc status. Reference values must be adjusted for the status of lactation. The following table shows the suggested reference values to evaluate the zinc status in dairy cows:
sample reference values μg/l
serum 600* - 1140
plasma 730** - 1240
whole-blood 2000 - 3500
hair 100 - 420
urine 20 - 370
*serum: 0-2 weeks p.p.: 460 μg/l, 3-5 weeks p.p.: 570 μg/l
**plasma: 0-2 weeks p.p.: 620 μg/l, 3-5 weeks p.p.: 720 μg/l