Feed Management - November/December 2017 - 30
30 ❙ FeedManagement
DAIRY COW TRACE MINERAL STATUS
Liver samples most accurate
Liver tissue samples are often considered the
most accurate regarding mineral status but are obviously more invasive to obtain. Despite this, liver
concentrations are not always associated with disease presence. However, changes in concentration
in the transport pool (usually blood and/or serum)
are often buffered via release of mineral from the
liver storage pool, suggesting liver status may be a better
indicator of dietary adequacy.
Analysis of the activity of mineral-specific enzymes
(e.g., glutathione peroxidase), i.e., the functional pool,
possibly is more appropriate for determining clinical deficiency disease.
Other testing samples
Urine is popular for attempting to assess mineral status, especially during the transition period. However, results are significantly affected by hydration status so correction factors, such as mineral-to-creatinine ratios should
be employed to remove this effect.
Milk mineral content is affected by parity and stage of
lactation and levels of some minerals are regulated.
Hair sampling is becomingly increasingly popular in
How nutrition influences dairy
cow health, immunity: www.
other species. Mineral concentration in hair is affected by
growth cycles and the piece sampled reflects the mineral
concentration at the time that hair was made, rather than
real time. There is also an element of "contamination" due
to exposure to sebaceous, apocrine and eccrine secretions.
Relation of hair values to other indicators of deficiency is
poor and few reference values exist.
Individual mineral analysis
Low levels of serum calcium and magnesium are
related to a metabolic deficiency, whereas bone concentration gives a better indicator of a long-term, true
deficiency. For dairy cows, it's usually the metabolic
issues that are of interest, so the use of serum values
is advocated. Phosphorous requires bone to give an
accurate idea of status, and other parameters should
www.WATTAgNet.com ❙ November/December 2017