Chemical analysis of hair samples has been used to identify the presence of chemical residues such as drugs and heavy metals, and also nutrients in an attempt to assess the whole body nutritional status of an animal. Although hair analysis has been around for several decades, its history is a checkered mix of success and failure. Testing is beset with factors which confound accurate interpretation of results, such as coat colour, contamination with environmental materials from soil, smoke, dust, shampoos etc. as well as the impact of climate, temperature, hormones and so on.
Hair testing has value in the assessment of exposure to several drugs, both therapeutic medicines and controlled drugs like opiates, barbiturates, and clenbuterol. It can also be used to establish long term exposure to toxic heavy metals like Mercury, Lead, Cadmium and Nickel. However, as a tool to assess the current nutritional status of a subject horse it has major limitations and is not as reliable as alternative methods.
Testing, if performed properly, requires mass spectrometry involving multi element analysis of a sample of at least 50g of hair, which is quite a lot. Any other form of testing, or tests performed on a smaller than 50g sample, should be regarded with extreme skepticism.