Do the Math for Improved Equine Nutrition

By Juliet M. Getty, Ph.D.

Do the Math for Improved Equine Nutrition

by Juliet M. Getty, Ph.D.

Reading a hay analysis report or trying to interpret nutrient levels in feeds and supplements can feel overwhelming. Yet when it comes to key nutrients, selenium, for example - a little bit of simple math can make a meaningful difference to your horse's health. 

Feed tags and hay analyses often list nutrient concentrations as "ppm," or parts per million. If that sounds confusing, you're not along. Fortunately, ppm is easier to understand than it appears. It simply means milligrams per kilogram (mg/kg) of feed - because one milligram is one-millionth of a kilogram. So, when you see ppm, you can think in terms of mg/kg. From there, the only step is to make sure your feed amount is expressed in kilograms (rather than pounds) and the math becomes straightforward.

Consider this example

Your hay contains 0.2 ppm (mg/kg) of selenium. How many mgs of selenium does 20 lbs of hay contain?

First, you need to covert 20 lbs to kgs. Since there are 0.454 kg in one pound, make the conversion by multiplying pounds by 0.454:

20 lbs of hay X 0.454 kg/lb = 9.08 kg of hay

Now that you have the number of kgs, you're ready to calculate mg of selenium:

9.08 kg of hay X 0.2 mg/kg (ppm) = 1.816 mg of selenium in your 20 lbs of hay.

Here's another example... 

There are 150 ppm of copper in one ounce of your vitamin/mineral supplement. How many mg of copper are you feeding per one-ounce serving?

Here you have to know that one ounce by weight equals 28.35 grams. 

Step 1: Convert 28.35 grams to kg:

28.35 grams of supplement divided by 1000 = 0.02835 kg

Step 2: Multiply kg of hay by ppm:

0.02835kg X 150 mg/kg (ppm) = 4.25 mg of Copper

Formulas to remember when working with ppm

  1. Convert lbs to kg: lbs x 0.454 = kg OR
  2. Convert ounces to kg: Ounces X 28.35 grams divided by 1000
  3. Calculate to find mg: kg X ppm (or mg/kg) = mg

What about percentages? 

The concentration of many nutrients can be presented as a percentage instead of ppm. Crude protein, ESC (simple sugars) and major minerals (such as calcium and phosphorus) are typically measured as grams. 

When you see a percentage, it simply means "parts per hundred." In other words, 8% protein means 8 grams of protein per 100 grams of feed. 

Let's say you would like to know the number of grams of protein in 20 lbs of your horse's hay. Your analysis says that it contains 8% crude protein... 

Step one: Convert lbs of hay to grams:

20 lbs of hay X 454 grams per lb = 9080 grams (Note, now we multiply by 454 instead of .454 because we're wanting grams, not kg).

Next: Multiply the grams of hay by the percentage (move the decimal over two places):

9080 grams of hay X 0.08 = 726.4 grams of protein.

Formulas to remember when working with percentages:

  1. Convert lbs to grams: lbs x 454 grams/lb
  2. Calculate to find grams: Grams X Percentage (move left two decimals)

Bottom line

Whether a nutrient is listed as ppm or as a percentage, it’s simply a measure of concentration—and with a quick conversion, you can determine exactly how many grams or milligrams your horse is receiving.

For Permission to Reprint

For permission to reprint this article, in part or in its entirety, or arrange for a private consultation, please contact Dr. Getty directly at gettyequinenutrition@gmail.com.