Research result: nutritional deficiencies are not measurable in horsehair

Background
Trace elements, such as copper, zinc, selenium and iron, for example, are an important part of a healthy ration for horses. However, it remains difficult to know for sure whether your horse is indeed deficient. Most horse owners feed supplementary trace elements based on an assessment of the horse's needs. To make this estimate, a forage analysis can give a good impression of what your horse is taking in. However, this analysis does not show what is actually absorbed by the horse's body. A blood or urine test does give a picture of what is currently circulating through your horse's body, but that is only a snapshot.

If your horse ingests too much of a particular trace element, something that can be harmful to your horse, you will not see it reflected in the blood values. Often, the liver then acts as a repository. The most reliable estimate is therefore obtained when you measure the horse's liver values. They also call this the 'gold standard'. To determine liver values, however, a vet has to take a liver biopsy. Something that is not only expensive, but also relatively invasive. Precisely the reason to look for a reliable alternative, such as a hair analysis.

Research
The reliability of a hair analysis has been studied by the GD and Pavo. For this study, hair and liver samples were collected from horses presented at two Dutch slaughterhouses. These samples were analysed by the GD laboratory for, among others, copper, zinc, selenium and iron, four important trace elements for horses. The values were compared with each other.

It was expected that the values in the hair and liver would match, but no correlation could be found here. So this means that hair analysis is unfortunately not a good method for reliable determination of trace element status in horses. Therefore, no appropriate feed advice can be given on the basis of a hair analysis.

Scientific publication
The study was published in the Journal of Veterinary Diagnostic Investigation, entitled 'Evaluation of hair analysis for determination of trace mineral status and exposure to toxic heavy metals in horses in the Netherlands' by van der Merwe et al 2022.

Read more here: https://pubmed.ncbi.nlm.nih.gov/35918902/