How to diagnose trace elements deficiencies ?
As explained in the module « Importance of trace elements in animals », there are two types of deficiencies: clinical and subclinical deficiencies.
Clinical signs are general and sometimes not too specific for some of them: diarrhoea, skin disorders, weak calves at birth, white muscle disease.
Subclinical issues are more difficult to link to trace elements deficiencies: low ADGs, reproduction issues, poor milking start, etc.
If the issues are confirmed or in case of overall assessment of the herd, an accurate diagnostic should be required. Solutions exist and should be managed with the veterinarian:
Trace element profile can be obtained by different samples: blood, milk, saliva or animal tissues.
Plasmatic profile in trace elements can be obtained in various ways :
- Direct, by measuring plasmatic concentrations of the elements: standard method the most commonly used as simple and convenient to establish.
- By assessing the activity of certain enzymes or hormones of which the functioning and the concentration depend on specific trace elements.
- Or by measuring the concentration of certain metabolites which accumulate when there are deficiencies (for instance T4 thyroid hormone which reflects the Iodine concentration, or the GsH-Px antioxidant enzyme which reflects the food supply in Selenium from 2 to 3 months ago): however, this indirect measure is only possible if there are clinical signs, which means the deficiency is quite serious.
Let us go back in detail on the advantages of the direct method, the measurement of the plasmatic concentrations of the elements :
- Standardized method, thus repeatable
- Method for determining the dosage with using plasma torch together with ICP-MS mass spectrometry, fast and precise (Chappuis & Poupon, 1991; Lumet & Negriolli, 2007)
- Affordable price for the analysis for a routinely basis
- Individual bloods analysis very reliable (on contrary of pool bloods – mix of bloods of which the interpretation of the results can be difficult and incorrect)
Note is made of the importance of doing these samples with an independent laboratory: it will guaranty objectivity of the results and the interpretations.
Precautions of use :
Several precautions when choosing the animals to sample need to be taken: Animals in the month pre or post calving should be excluded, healthy animals should be chosen and at different physiological stages.
The minimum number of animals to sample varies between 4 and 12 from an author to another (Herdt & Hoff, 2011; Kincaid, 1999; Oetzel, 2004). 5 is generally what is practiced.
The tubes used by veterinarians for this type of sampling are specific: indeed, tubes made of glass or those with a rubber cork are at risk to contaminate the sample, favouring hemolysis or by artificially increasing the Zinc level.
Precautions to take when sampling are clear: favour blood sample at the jugular, in order to limit faecal contaminations, and on the muscular cells. Spontaneous blood flow in the open tube will be preferred in order to limit hemolysis (rupture of red blood cells).
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Sample of tissues
These samplings allow an access to different trace elements stocking organs.
Liver biopsy is very relevant for certain trace elements such as Cu, Zn, Fe, and secondary Co, Mn, and Se. In case of poisoning, it can also be interesting.
Indeed, throughout a longer fasting period, stress or inflammatory or infectious conditions – even starting – the quantities of stocked trace elements are changed before apparition of any clinical sign or any variation of the plasma concentrations (Suttle, 2010). Even if easy to do, liver biopsy is more expensive and slower than a blood sample.
For Iodine and Selenium, excreted amounts in the milk reflect the short-term status of the animal. The analysis can be done on either one individual or on the milk from the tank. However, some contaminations by the blood cells could distort the analysis (Guyot, Saegerman, Lebreton, Sandersen, & Rollin, 2009). Moreover, when using iodine-based products, this sampling is useless as the products artificially increase the iodine level measured (Meschy, 2010).
Urinary and hair profiles could seem interesting at first sight because easy to do. However, they are not the most relevant samples. Indeed, urinary concentration in trace elements are not correlated to blood concentrations. For instance, hair concentrations highly vary depending on the colour: black hair are richer in Zinc, red hair are richer in Copper. Furthermore, hair is very often contaminated by the external environment (when friction against the fence for example) and dust. Therefore, hair concentrations in trace elements depend more of the hair colour, the age of the animal and the external environment than of his status (Meschy, 2010; Siliart, 2011, 2014).