Is hair analysis a reliable way to evaluate your horse’s mineral status?

Mineral testing is an important aspect of monitoring your horse’s health, especially if forages in your area are known to be deficient or excessive in a given nutrient. Horses with certain medical conditions may also need frequent monitoring of mineral levels.

In horses, mineral status is most commonly assessed through blood testing, hair samples or by evaluating intake with a forage analysis. These methods each have advantages and disadvantages that impact their usefulness.

Hair sample analysis is convenient, but few reference ranges have been established for mineral levels in equine hair, making interpretation of results difficult.

Hair analysis is currently only considered reliable for assessing heavy metal levels in the horse’s body.

If you are concerned about your horse’s mineral status, consult with your veterinarian about the best form of testing given your horse’s health issue(s). Some signs that your horse may have abnormal mineral status include poor or abnormal growth, dull coat, lethargy or changes in appetite.

Hair Mineral Analysis for Horses

Hair mineral analysis is conducted by cutting hair from your horse’s mane or tail and sending it to a laboratory for analysis.

The theory is that mineral concentrations in the hair will tell you if your horse’s diet is deficient or excessive in any minerals.

Hairs from the mane and tail are used because these hairs grow continuously throughout the year and are not affected by seasonal shedding. [1]

A hair mineral analysis report will typically provide levels of:

  • Macrominerals: Calcium, magnesium, sodium, potassium
  • Trace minerals: Zinc, copper, selenium, iron, chromium, manganese, cobalt, boron, molybdenum
  • Heavy metals: Arsenic, cadmium, lead , aluminum, mercury

Purported Advantages

As a potential marker for mineral status, hair is appealing for several reasons:

  • Easy to obtain – a horse owner can collect the sample
  • Easy to store – can be placed in a plastic bag and stored at room temperature without degrading
  • Long-term status – may provide information on mineral intake throughout the lifespan of the hair strands [2]
  • Not as tightly regulated – May not be under homeostatic control (unlike blood concentrations)
  • Measures accumulation – Some minerals become concentrated in the hair, making them easier to measure [3]

Better Alternatives

Although hair analysis is an appealing option, it is not the best approach for assessing your horse’s mineral status, as will be discussed below.

The best way to estimate how well your horse’s mineral requirements are being met is to submit a forage sample for analysis and evaluate your horse’s dietary intake.

An equine nutritionist can help you determine how well your feeding program meets your horse’s needs and how best to balance the diet.

Is Hair Mineral Analysis Accurate?

Minerals from circulating blood may be deposited in the hair as it grows. In theory, mineral levels in hair could reflect long-term nutritional status. [4]

However, whether mineral deposition in hair directly correlates with mineral levels in the blood or other tissues is debatable. It is also not clear how mineral levels in hair relate to dietary intake.

There have only been a handful of studies examining the relationship between mineral content in hair, dietary intake, blood, and liver levels.

Relationship with Mineral Levels in Blood

Blood tests accurately report mineral levels circulating in the bloodstream at the time of sampling. However, these levels can be significantly impacted by short-term factors, such as when and what the horse ate, whether they exercised recently, whether they are fighting an illness, etc.

This makes it hard to get an accurate idea of the horse’s long-term nutritional status. However, blood tests do reliably indicate long-term status for several nutrients, including the antioxidants selenium and vitamin E.

Several studies have examined the relationship between minerals in hair and blood. Unfortunately, no meaningful associations have been found for macrominerals or trace minerals. [3][5][6][7]

Minerals for which hair analysis is not reliable include: [3][5][6][7]

Heavy Metals

However, relationships have been found between blood values and hair content of heavy metals (e.g. cadmium, lead). [6][8]

Because heavy metals are usually very low in circulating blood, their levels are often below the detectable limit of current testing technologies.

Hair analysis is more reliable for heavy metals because these particles accumulate in the hair over time. They can become detectable in tests to give an indication of long-term heavy metal status.

Relationship with Mineral Levels in Liver

The liver stores many trace minerals and liver biopsies are sometimes used to assess long-term mineral status. However, liver sampling is an invasive procedure and is not frequently done.

Hair mineral analysis would be an attractive alternative, but thus far no significant correlations have been found between liver and hair trace mineral concentrations. [9]

Relationship with Dietary Intake

There does not seem to be a strong relationship between the dietary intake of most trace minerals and the concentration in the hair. [10][11]

However, one study did find that ponies fed more minerals had greater concentrations of those minerals in their hair. [12]

Selenium

Selenium is one trace mineral that may be useful to measure in hair. [9]

One study collected mane and tail hair samples from horses that had intermittently grazed a selenium-contaminated pasture over the course of 3 years.

They found that hair segments grown when horses were on the pasture had greater concentrations of selenium than hair segments grown when horses were not on the pasture. [2]

Note that the selenium levels in this pasture were much higher than typical (up to 127 ppm compared to 0.1 ppm). [2][13] Whether hair analysis would reveal differences in selenium intakes within more typical ranges is unknown.

This study found that hair selenium could be traced back three years and correlated with dietary intake. Still, the applications of tracing intake back that far in time may be limited.

A blood sample is more practical for estimating the horse’s current selenium status.

Factors Affecting Hair Mineral Analysis

Why do so many studies find little to no correlation between hair analysis and other measures of mineral status?

Other factors besides dietary intake can affect mineral levels in hair including:

  • Hair colour: Melanin (the pigment in hair) may bind to copper and zinc, causing more variation in black hair than in other colours of hair. [3][14][15]
  • Location of hair: Samples obtained from body hair, mane hair, and tail hair give different results. [4]
  • Seasonal hair growth and shedding: Body hair is more affected by these factors than mane and tail hair. [1]
  • Age: Some minerals increase with age and others decrease. [3][16]
  • Products applied to the hair: Some products contain minerals that may contaminate the hair (e.g. zinc cream, fly spray).
  • Washing method of the hair: Insufficient or no washing may leave dirt, sebum, or products on the hair that may artificially increase the mineral concentrations measured by hair analysis. [3]
  • Sex: Mares have over 50% higher levels of some minerals than stallions. [17]

Limitations of Hair Mineral Analysis

Hair mineral analysis appears most reliable for assessing long-term heavy metal exposure.

However, there are currently no universal reference ranges in horses for acceptable concentrations of heavy metals in hair.

Although some studies have proposed reference ranges, these vary by location and intake of heavy metals. [14][16][18][19][20]

More research is needed to evaluate the relationship between heavy metal levels in hair and clinical symptoms.

Lab Variation

In addition, there is significant inter- and intra- lab variation in the results obtained when a sample is analyzed. This means that the same sample sent to multiple labs or analyzed several times in the same lab can yield different results. [21][22]

In a recent study, horse hair analysis reports from three different labs in Germany gave vastly different results. The difference between labs for individual minerals ranged from 10% to 58%. [22]

In addition, different laboratories may present the results with different reference ranges. A mineral level that one lab considers within the normal range may be classified as deficient or in excess by another lab.

This makes it difficult to understand the clinical relevance of results and may lead to false conclusions about how to address the horse’s mineral needs. [22]

When is Hair Mineral Analysis Useful?

A hair mineral analysis may be useful in cases of suspected heavy metal poisoning.

This is most likely to occur if horses are grazing near industrial areas where pasture is contaminated with heavy metals or are consuming forages grown in these areas.

High exposure can also occur next to areas with heavy vehicle traffic. [26]

Signs of Heavy Metal Exposure

In general, heavy metal exposure increases oxidative stress in cells.

Based on research in humans and other animals, suspect a high burden of heavy metals in your horse if you observe: [23][24]

  • Abnornmal liver function tests
  • Changes in behaviour
  • Muscle weakness
  • Tumour development
  • Weakened bone health
  • Poor kidney function
  • Anemia
  • Emphysema
  • Chronic rhinitis – sneezing & coughing

Testing for Prohibited Substances

Hair analysis can also be reliable for detecting some banned substances in high-level sport horses.

Detectable levels of the banned antibiotics metronidazole, trimethoprim/sulphadiazine, and procaine were found in tail hair after 5 to 10 days of treatment with these medications. [25]

Submitting a Hair Sample for Analysis

Mane hair grows at a rate of 2 cm per month. [22] You can theoretically analyze the mineral status within a specific time frame depending on where you cut the mane hair sample.

To analyze recent mineral status, cut the hair as close to the skin as possible. Mane hair can be collected from the top of the neck using stainless steel scissors that can be disinfected between samples.

Laboratories typically require at least 0.5 grams of hair sample. [22]

Interpreting Results

Given the poor reliability of hair analysis for macro- and trace- minerals, results should be interpreted with caution. Reference ranges are lacking.

If your horse’s hair analysis indicates high levels of heavy metals, rule out possible sources of contamination during sample collection, such as hair products or washing techniques.

Confirming where your hay or other feeds are grown may help identify the source of heavy metal exposure.

Also, consult with your veterinarian to assess health implications for your horse. Long-term exposure to heavy metals may affect the function of many body systems.

Your veterinarian may be able to assess the extent of damage through additional tests. Based on these results, your vet may suggest a specific treatment or course of action.

Following removal of the heavy metal source, ensure that you are feeding a well-balanced diet to support metabolic processes and detoxification systems. In particular, pay attention to liver health since the liver is a major site of heavy metal accumulation.

Heavy metals induce oxidative stress through the production of free radicals (oxidants). Ensure your horse’s diet provides adequate antioxidants, including Vitamin E, Vitamin C, selenium, zinc and copper. [23]

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Summary

Hair analysis may be useful for determining if a horse has been exposed to heavy metals. These elements are typically difficult to detect in the blood but accumulate in hair.

However, hair trace mineral levels are generally not well correlated to blood mineral levels or intake. Therefore, hair analysis is not accurate for evaluating whether a horse is getting adequate minerals in their diet.

The best way to determine if your horse is receiving sufficient vitamins and minerals is through forage analysis and assessing their feed and supplement intake.

For personalized feeding recommendations, submit your horse’s diet to receive a free customized feeding program designed by a qualified equine nutritionist.

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References

  1. Dunnett, M. and Lees, P. Trace element, toxin and drug elimination in hair with particular reference to the horse.
  2. Davis, T.Z. et al. Analysis in horse hair as a means of evaluating selenium toxicoses and long-term exposures. J Agric Food Chem. 2014.
  3. Brummer-Holder, M. et al. target=”blank” rel=”noopener noreferrer”Interrelationships between age and trace element concentrations in horse mane hair and whole blood.
  4. Combs, D.K. et al. Mineral concentrations in hair as indicators of mineral status: A review. J Anim Sci. 1982.
  5. Biricik H. et al. Seasonal changes of some mineral status in mares. J Eq Vet Sci. 2005.
  6. Fazio, F. et al. Bioaccumulation of mineral elements in different biological substrates of athletic horse from Messina, Italy. Animals. 2020.
  7. Wysocki, A.A. and Klett, R.H. Hair as an indicator of the calcium and phosphorus status of ponies. J Anim Sci. 1971.
  8. Janiszewska, J. and, Cieśla, A. Concentration of cadmium and lead in horse blood serum and hair in relat
  9. Van der Merwe, D. et al. Evaluation of hair analysis for determination of trace mineral status and exposure to toxic heavy metals in horses in the Netherlands. Journal of Veterinary
  10. Palm, F. et al. Analysis of selenium, zinc and copper in hair of horse mares and their neonates. Tierärztliche Umschau. 2012.
  11. Wells, L.A. et al. Mineral intake and hair analysis of horses in Arizona. J Eq Vet Sci. 1990.
  12. Ghorbani, A. et al. Effects of dietary mineral intake on hair and serum mineral contents of horses. J Eq Vet Sci. 2015.
  13. Filley, S.J. et al. Selenium Fertilization of Pastures for Improved Forage Selenium Content. Prof Anim Sci. 2007.
  14. Asano, K. et al. Influence of the coat color on the trace elemental status measured by particle-induced X-ray emission in horse hair. Biol Trace Elem Res. 2005.
  15. Szpoganicz, B. et al. Metal binding by melanins: studies of colloidal dihydroxyindole-melanin, and its complexation by Cu(II) and Zn(II) ions. J Inorg Biochem. 2002.
  16. Asano, R. et al. Concentrations of toxic metals and essential minerals in the mane hair of healthy racing horses and their relation to age. J Vet Med Sci 2002.
  17. Kalashnikov, V.V. et al. Assessment of Gender Effects and Reference Values of Mane Hair Trace Element Content in English Thoroughbred Horses (North Caucasus, Russia) Using ICP-DRC-
  18. Asano, K. et al. Twenty-eight element concentrations in mane hair samples of adult riding horses determined by particle-induced X-ray emission. Biol Trace Elem Res. 2005.
  19. Kalashnikov, V.V. et al. Reference intervals of essential and toxic elements concentrations in mane hair and blood serum of Arabian purebred horses. IOP
  20. Namkoong, S. et al. Reliability on Intra-Laboratory and Inter-Laboratory Data of Hair Mineral Analysis Comparing with Blood Analysis. Ann Dermatol. 2013.
  21. Wahl, L. and Vervuert, I. Commercial hair analysis in horses: A tool to assess mineral intake?. J Equine Vet Sci. 2022.
  22. Flora, S.J.S. et al. Heavy metal induced oxidative stress & its possible reversal by chelation therapy. Indian J Med Res. 2008.
  23. Cygan-Szczegielniak, D. et al. Concentration of Selected Essential and Toxic Trace Elements in Horse Hair as an Important Tool for the Monitoring of Animal Exposure and Health.
  24. Dunnett, M. and Lees, P. Hair analysis as a novel investigative tool for the detection of historical drug use/misuse in the horse: a pilot study. Equine Vet J. 2004.
  25. Ward, N.I. and Savage, J.M. Elemental status of grazing animals located adjacent to the London Orbital (M25) motorway. Science of the Total Environment. 1994.