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The aim of this study was to develop a recommendation for the evaluation of the selenium status in dairy cows under consideration of different test mediums and techniques. In addition, an overview about the effects of selenium on the body function of dairy cows was discussed. Three different data sets obtained by the department of herd-health of the Clinic for Ruminants and Swine of the Free University of Berlin were evaluated (“Bestandsdatei 1”, “Bestandsdatei 2”, “Betriebsuntersuchung”). Each set contained data from different herds which averaged 581 Holstein-Frisian cows bred and kept in East Germany. “Bestandsdatei 1” was divided into two study subgroups due to a change of method of analysis of serum selenium (P1: from 1995 to 2006 / P2: from 2006 to 2010). In P1 2084 pooled serum samples from 578 farms and in P2 1188 pooled serum samples from 320 farms were evaluated. Mean serum selenium of P1 was 72 ± 22.8 μg/l and of P2 98 ± 26.9 μg/l. While the results of P1 showed selenium deficiency, P2 did not.
“Bestandsdatei 2” was a part of “Bestandsdatei 1, which contained data evaluating selenium n pooled samples of serum, plasma, urine, whole-blood and hair. In “Betriebsuntersuchung” selenium was measured in individual samples of serum, plasma, urine, whole-blood, hair and liver biopsies. There was no significant correlation between selenium and milk yield, the incidence of ovarian cysts, mastitis and retained placenta. In addition, only low, but significant correlations between the selenium content in serum and other trace and mineral elements and vitamins were determined. All tested mediums (serum, plasma, whole-blood, urine, liver, hair) can be used to evaluate the selenium status. While hair and whole-blood has proven to be the most suitable medium for long-term evaluation of the selenium status, serum, plasma and urine can be used to establish the current status. However, plasma is recommended over serum as it does not undergo coagulation which decreases the selenium concentration by 15.3 μg/l on average. Although urine has shown to be a sensitive parameter, further research is necessary before recommendations regarding the use of urine for the evaluation of the selenium status can be given. The selenium concentration in serum, plasma, urine and liver varies due to season and lactation-cycle. The lowest selenium values were measured in summer and for dry- and closeup cows. Nevertheless, taking these variations into account reference ranges could be established for the different test mediums and are listed below. A beneficial selenium status includes a improved immune defence without reaching the range of a subclinical selenoses.