Q.​ What’s the best way to discover any nutritional deficiencies your horse might have: a blood test, a hair analysis, or both? And is there one test that does everything?

—Kerry, via e-mail

A. Checking your horse for nutritional deficiencies is a good idea, because living long-term with even suboptimal nutrition might have health or performance consequences. As you mention, there are various ways to assess nutrient status, including bloodwork, hair analysis, and looking at the dietary levels of the various nutrients.

Bloodwork such as a basic complete blood count (CBC) can tell you quite a lot about your horse’s overall well-being. However, it’s not as effective for determining whether your horse has nutrient deficiencies. Minerals such as calcium are very tightly controlled by the body to maintain blood levels within a relatively small range. This means blood levels of calcium might appear normal when, in reality, body stores are low. In this instance, your horse would be mobilizing calcium from bone stores to maintain blood levels. When interpreting this result, you might think the diet is meeting your horse’s calcium requirements when it’s not.

Iron is another mineral that blood levels do not accurately reflect. A more complex set of blood analysis is needed to look at ferritin and transferrin (two types of blood proteins) levels, which give better indications of the body’s iron stores and free iron.

You can use bloodwork to evaluate vitamin E levels, which I highly recommended for horses with limited access to fresh pasture. Bloodwork can also be used to assess selenium levels. Remember, however, that bloodwork only shows you the status of that mineral in the moment in which the blood was drawn. Some mineral levels vary quite dramatically with work and time since eating, making interpretation and identification of excesses or deficiencies more difficult.

Hair analysis is not as variable; however, it is also not a current picture. Results from analyzing hair samples create a picture of what was happening over the past several months, which may not be representative of the current diet. You can send hair samples to a wide variety of labs, but each facility will have its own set of normal ranges, which can complicate interpretation. Additionally, many places that offer hair analyses are also selling supplements, which might be considered a conflict of interest. Contamination of hair samples, especially with dirt, is fairly common and can impact results. If submitting hair for analysis, be sure to follow the lab’s instructions for collecting a sample carefully.

Because bloodwork might not accurately reflect deficiencies and hair testing is a look at history rather than current events, the best way to evaluate whether nutritional deficiencies exist is to look at the diet. The only way you can increase or decrease your horse’s nutrient levels, such as minerals, is through diet changes—making sure it meets all his needs and is properly balanced. And the only way for most minerals (calcium, zinc, copper, etc.) to get into the horse is through the diet. So if the horse’s diet is deficient or unbalanced, he’s going to be fighting an uphill battle with regard to having adequate levels of these nutrients. 

Therefore, when looking for nutrient deficiencies, I always like to start with an evaluation of the current diet. From there, if it looks like the horse might be deficient in certain nutrients or I want a more complete picture, I request bloodwork to be done. Then we can create an appropriate diet that will ensure the horse is receiving adequate levels of all nutrients.

Unfortunately, no one test does it all, but by working with a qualified equine nutritionist you will find that it’s a fairly straightforward process to have your horse’s diet evaluated and to determine potential areas where issues might exist.