Hair testing in horses has many uses, unfortunately as a guide to mineral deficiencies or to diagnose veterinary conditions are not amongst them.

Attempts have been made to use hair analysis as an indicator of the whole body status of minerals, such as calcium and phosphorus and trace metals such as copper, molybdenum, zinc, selenium and iron. However, hair content does not correlate with whole body levels and the validity of the approach in the horse remains to be confirmed.

It can provide a glimpse into dietary mineral intake over the previous 6 months. A single result from one horse cannot be used for other horses or to make general recommendations. Many factors influence hair mineral levels – so you may be able to pin-point, others you won’t.

Hair analysis can be useful for measuring heavy metals such as selenium, mercury, arsenic, lead and cadmium. Samples are easily collected, stored and transported. However, factors affecting the reliability of hair analysis, include the following:

• hair absorbs minerals the environment and therefore hair levels are not indicative of body status, for example a mild zinc deficiency causes a reduction in hair zinc levels, but not in hair growth rate, whereas a severe zinc deficiency slows hair growth so that the zinc concentration rises to normal or above normal

• shampoo, coat-conditioners, age, hair thickness, colour, breed, gender, sire, body location, season and rate of hair growth all affect mineral levels

• coloured hair has higher concentrations of calcium and selenium than white hair taken from the same horse. Same occurs in dogs and cattle.

• grey hair contains significantly greater amounts of copper, titanium and zinc and lesser amounts of boron, calcium, selenium and strontium than other colored horse hairs

• hair from young animals is often lower in zinc, manganese and iron, but higher in sodium, calcium, copper and potassium than that from older animals

• pigmented hair is higher in calcium, magnesium, potassium and sodium than unpigmented hair

• black hair contains more sodium, phosphorus, potassium, magnesium and calcium than chestnut hair

• the effect of body location on mineral content of hair may be due to differences in surface contamination, differences in hair growth cycles and differences in texture of the hair

• levels of most minerals except copper are lower in hair in winter than in summer; other studies found the opposite to be true with higher concentrations of minerals in all hair samples collected in winter

• because hair absorbs minerals by exchanging them for other minerals, the level of the absorbed mineral increases while the concentration of the exchanged mineral decreases

• methods of analysis differ between laboratories in terms of decontamination from environmental contaminants, digestion method, trace element recovery rates and minimum detection limits.

Hair testing is most useful for detecting heavy metal toxicosis (such as arsenic, cadmium, lead, mercury and selenium), anabolic steroids and drug misuse. For selenium, the sample must be collected from growth that occurred during the time of excess selenium intake and results will depend on the form in which the selenium was consumed. In contrast to urine and blood analyses, hair analysis can detect and quantify drugs weeks, months or even years after administration or intake.

Hair testing can be important during a pre-purchase veterinary examination to identify misuse of anti‐inflammatory and sedative drugs. It can provide a historical record of drug (or other chemical) exposure, even though some losses may occur due to chemical change or leaching out. As well as detecting drugs or chemicals retrospectively months or years after systemic exposure, hair root analysis may indicate acute exposure to codeine.

Because of the many factors that cause variation in mineral content of hair, hair analyses are not likely to be precise indicators of the mineral status of animals. However, if you’re considering hair analyses, ensure the reference values are from horses of similar breed, sex, season, sire, age and color. As a check, if you wanted to have hair analysis done, it might be worth sending several samples from one horse or the same sample to several different laboratories and comparing the results.

Blood work is definitely not reliable for most minerals. In my experience, basing supplementation on diet analysis is the most reliable way to assess mineral intake. 

EQUINE CLINICAL NUTRITION
Dr Jennifer Stewart