[Zinc concentrations in different sample media from dairy cows and establishment of reference values]

Zinc plays an important role in many body functions, including health and fertility. The assessment of the zinc supply can be performed using blood, urine and hair. The objective of this study was to establish reference values for herd analysis for the different sample media and stages of lactation in German dairy herds.

The data of 1515 herds, which had been visited by the Clinic for Ruminant and Swine, Free University of Berlin, Germany, between 1995 and 2012 were analyzed. Serum, plasma, whole-blood, hair and urine zinc concentrations of pooled samples with 7 to 10 cows per group were determined. In herds with more than 200 cows, five groups were sampled (8-3 weeks ante partum [a. p.], 3-0 weeks a. p., 0-1 week post partum [p. p.], 3-5 weeks p. p. and 15-18 weeks p. p.). In herds with fewer than 200 cows, only four groups were sampled (8-3 weeks a. p., 3-0 weeks a. p., 0-5 weeks p. p. and 6-20 weeks p. p.).

Correlations among zinc concentrations in different sample media varied between r = 0.001 (whole blood and urine) and r = 0.75 (serum and plasma). Serum and plasma zinc concentrations changed rapidly and followed a lactation dynamic, with the lowest values around parturition. Whole-blood and hair zinc concentrations changed slowly but displayed a similar decrease a few weeks after parturition. Reference values for pooled samples for the different sample media and stages of lactation are proposed.

When assessing the zinc supply, different reference values have to be applied for the different sample media and stages of lactation. For repeated analysis to evaluate changes in zinc nutritional status, the same sample medium and stage of lactation should be used.