Developing Trace Mineral Status

Trace mineral deficiencies can have a dramatic impact on animal performance. In order to gain a better understanding of trace mineral status, body tissues (i.e. blood, liver, etc.) may be sampled. However, trace mineral content of some tissues may not be reflective of trace mineral status of the animal and may result in erroneous conclusions.

While blood is a suitable tissue to sample to assess iodine, iron (saturation of iron binding proteins) and selenium (glutathionine peroxidase activity) status in cattle, it may not be an appropriate tissue to sample to assess status of other trace minerals (52; Table 6).

Liver is a better indicator of manganese and selenium status than blood (Table 6). Liver vitamin B12 or a combination of serum vitamin B12 and serum methylmalonic acid concentrations can be used to assess cobalt adequacy of the diet (52). Zinc concentration in liver is a better indicator of zinc status than serum or plasma zinc concentration, although zinc levels in liver are affected by bacterial infections, stress and life cycle stage (52).

Liver copper levels are a better indicator of copper status of the animal than serum copper levels. Serum copper levels are a poor indicator of copper status of the animal, as serum copper levels do not change significantly until liver copper stores are virtually depleted (52). Furthermore, copper present in serum may not be available to the animal. In situations where animals are consuming diets high in molybdenum and sulfur, one of the species of thiomolybdates that forms, MoOS₃^2-, trithiomolybdate (TM₃), can be absorbed by the animal. The absorbed TM₃ binds to copper present in the serum, rendering it unavailable to the animal. In addition to sampling liver to assess copper stores of the animals, sampling blood to determine ceruloplasmin levels may be prudent to determine copper availability.

Table 6. Relative Value of Live and Blood in Assessing Trace Mineral Status