Q: I have difficulty interpreting the nutrient analysis listed on feed tags and understanding what the mathematical conversions really mean for my horses. Are their any simple mathematical formulas to follow?

By Juliet M. Getty, PhD

A: Reading a hay analysis or puzzling over the ingredients in feeds or supplements can be a chore, yet when considering particular elements —selenium, for example — some minor math can make a major difference to your horse’s health. 

Feed tags and hay analysis often list ingredients as “ppm” or parts per million. Does this confuse you? You aren’t alone. 

The best way to think of ppm is as milligrams per kilogram (mg/kg) of feed (since a mg is a one millionth “part” of a kilogram. Therefore, when using mg/kg, you have to make sure you’re dealing with kg of feed instead of pounds (lbs) in order to make your calculations.

Consider this example: Let’s say your hay contains 0.2 ppm (mg/kg) of selenium. How many milligrams of selenium do 10 pounds of hay contain? 

First, you need to convert the pounds to kilograms. Since there are 0.454 kg in 1 pound, make the conversion by multiplying lbs by 0.454. So, 10 lbs multiplied by 0.454 equals 4.54 kg (10 x 0.454 = 4.54).

Now you’re ready to calculate the milligrams (mg) of selenium. Multiply 4.54 kg of hay by 0.2 ppm (or mg/kg) (4.54 x 0.2 = 0.91). That gives you 0.91 milligrams of selenium in your 10 pounds of hay.

Here are two valuable formulas to remember:

• Convert lbs to kg: lbs x 0.454 = kg
• To find mg: kg X ppm (or mg/kg) = mg

Juliet M. Getty, PhD is an independent equine nutritionist with a wide U.S. and international following. Located in Lewisville, Texas, her research-based approach optimizes equine health by aligning physiology and instincts with correct feeding and nutrition practices. Dr. Getty’s goal is to empower the horse person with the confidence and knowledge to provide the best nutrition for his or her horse’s needs.

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