First some basics. The metric system uses kilograms (equivalent to 2.2 lbs), grams and milligrams to weigh things.
Where we might use 3 or 4 ounces, in the metric system a similar convenient amount might be 100 grams.
- Kilogram (Kg or kg) - 1,000 grams
- Gram (g, gm) - a basic unit of weight
- Milligram (mg) - 1/1,000 of a gram; there are 1,000 mg in one gram
- Microgram (mcg or ยต) - 1/1000 of a milligram; there are 1,000 mcg in a mg
- PPM or ppm - parts per million which = mg/kg
- % or percent - 100ths of a gram per gram; how much (by weight) of an elemental mineral is in a gram of compound or product. The elemental mineral will show as a fraction [99% = 99/100 = 0.99 g]
In case you get lost, you can check your math at the Online Conversion site.
Because American supplements and feeds do still show pounds and ounces, you need to know that
- One pound = 453.6 grams; there are 2.2 lbs in a kilogram (1,000 g / 453.6 = 2.20]
- One ounce = 28.4 grams
You can also do metric to US weight conversions at the Online Conversion site.
Let's look at some examples.
A popular selenium yeast product shows the product analysis on the label as:
Active ingredients per 1 gram scoop - Selenium (as Selenium Yeast) 2,000 mcg
This really is a lot of information. You can divide 2,000 mcg by 1,000 to see that there are 2 mg selenium in one scoop.
Because the scoop size is given at one gram, you can see there are 453 scoops (or servings) in a one pound jar of this product.
Looking at some of the ingredients in another highly advertised product, we see:
Per 132 gram serving
Copper 13.2 mg
Iodine 660 mcg
This tells us that the serving size is approximately 4-1/2 ounces
[132 grams/28.4 grams = 4.6 oz]
You would need to use more than 890 grams (30 ounces) of this product to provide your horse's copper requirement of 90 mg/day.
[90 mg/13.2 mg = 6.8 servings x 132 grams per serving = 899 grams]
and [899 grams/28.4 grams = 31.6 oz]
So you can see this is not a cost effective product for supplying your horse's copper.
We also know that we want to give our horse 2-4 mg of iodine per day. At 660 mcg, this product only supplies 0.6 mg of iodine [660 mcg/1000 = 0.66 mg]
Here's another popular product with the analysis shown on their web site:
Phosphorus 1.25%
Magnesium 1.5%
Copper 500 ppm
Iron 350 ppm
Selenium 5 ppm
Iodine 8 ppm
Starting with copper (because copper is usually the first mineral I address when I'm evaluating a supplement), we see that this has 500 ppm, or 500 mg/kg. Dividing by 1,000 (remember, there are 1,000 grams in 1 kg) gives us 0.5 mg copper per gram of product. [ (500 mg/kg)/1,000 = 0.5 mg/gm]
If you multiply the grams by 28.4, you'll see there are 14.2 mg per ounce. So you will need around 6 ounces of this product to supply your horse's minimum 90 mg copper requirement.
[500 ppm = (5 mg/kg)/1000 = 0.5 mg per gram] [ 0.5 x 28.4 = 14.2 mg/oz]
[need 90 mg / 14.2 mg/oz = 6.3 oz]
You could also divide the 90 mg requirement by the 0.5 mg/gm to see how many grams you would need to feed.
[90/0.5 = 180 gm] Divided by 28.4 should give us ounces [180/28.4 = 6.3 oz] which answer as the first method.
The feeding directions for this product call for 1 oz per 100 pounds body weight, so you can see this product will supply a generous level of copper.
Selenium, at 5 ppm, will supply 0.005 mg/gm, or 0.852 mg in a 6 ounce serving. This would be about right for your 600 lb pony.
[5 ppm = 5 mg/kg] [ (5 mg/kg)/1000 = 0.005 mg/gm] [0.005 x 28.4 = 0.142 mg/oz] [0.142 x 6 = 0.85 mg in 6 oz]
Exercise -try working out the phosphorus, iron and iodine levels in a six ounce serving. The answers are at the end of this post.
Working out the levels of a mineral or nutrient in a fortified feed follows the same math except you convert to pounds or kilograms instead of ounces
Calcium (min) 2%
Phosphorus (min) 1%
Copper (min) 130 ppm
Selenium (min) 2.3 ppm
The (min) indicates that the product contains at least (minimum) this level of nutrient; exact levels are more difficult to control in the larger bulk of feed vs the smaller, more precise requirements of a supplement.
Like most fortified feeds, it is "balanced to itself" i.e. it will have correct Ca:P and trace mineral ratios independently of any other forage/feed you are providing. [Calcium 2% / Phosphorus 1% = 2:1]
Because we'll feed this in pounds (or kilos), we'll figure the levels for 1 pound and for 1 kg (2.2 lbs).
Calcium 2% divided by 100 gives 0.02 grams calcium per gram of product. Multiply by 453.6 for grams per pound. Multiply by 1,000 for grams per kilogram.
[2% / 100 = 0.02 g/gm] [0.02 x 453.6 = 9.07 g calcium per pound] [0.02 x 1000 = 20 g calcium per kilogram]
Copper 130 ppm divided by 1,000 gives 0.13 mg per gram. Multiply by 453.6 for mg per pound; by 1,000 for mg per kg.
[130 ppm = (130 mg/kg)/1000 = 0.13 mg/gm x 453.6 = 59 mg copper per lb of feed]
[130 ppm = 130 mg/kg - well, we don't have to go any further to see how many mg of copper are in a kilogram of feed]
Try working out the Phosphorus and selenium levels and check your results against the answers below.
By now you are either digging through your tack room looking for feed bag and supplement labels to practice on or you are reaching for a cold one having thrown your calculator in the trash (you didn't try to do this by hand, did you?) Either way, I hope this gives you some ammunition against snake oil products and helps you choose appropriate feeds and supplements. If you have a question, you can enter it as a comment to this post or email me directly at DesertEquineBalance@gmail.com.
Exercise answers:
Minerals in 6 ounces of popular supplement
Phosphorus 1.25%
[1.25/100 = 0.0125 g/gm x 28.4 = 0.355 g/oz x 6 = 2.13 g Phosphorus in 6 oz supplement]
Iron 350 ppm
[350 ppm = (350 mg/kg)/1000 = 0.35 mg/gm x 28.4 = 9.94 mg/oz x 6 = 59.6 mg Iron in 6 oz]
Iodine 8 ppm
[8 / 1000 = 0.008 mg/gm x 28.4 = 0.227 mg/oz x 6 = 1.4 mg Iodine in 6 oz]
Minerals in 1 lb and 1 kg of a well know heavily fortified feed
Phosphorus (min) 1%
[1/100 = 0.01 g/gm x 453.6 = 4.5 g Phosphorus per pound of feed]
Selenium (min) 2.3 ppm
[2.3/1000 = 0.0023 mg/gm x 453.6 = 1.04 mg Selenium per lb of feed]
Go here to review the original Understanding Supplement Labels article.
