Figure 6:Trace elements in blood serum. The Co and Mn levels at all farms were far below the minimal reference level for nutrient sufficiency. Se levels in cows at all farms were within the Se reference range for nutrient sufficiency. Significant differences were seen between farm T with the highest level and the other farms (ab <0.001), and farm E with the lowest Se and the other farms, other than farm V (cd: p< 0.001). The average of Zn levels in cows on farms K, R, S and B were above the maximum reference level (150 μg/dL). All levels of Cu were within the reference range for nutrient sufficiency and significant differences were seen between animals on farm K and T (ab p< 0.001).