How to use nutrient analysis from a sample of hay/pasture/feed.  Every feed is comprised of two fractions, dry matter and moisture.  Since each of these feeds have differing moisture (water) content, we need a means to express them in the same terms.  Nutrients are reported as Dry Matter (DM) or on an As Fed basis.  It is easier to use the DM analysis since every feed will be expressed on an equal moisture basis.

Although nutrient content may be expressed in either means, calculating feed intake is used on an as fed basis.  We don’t feed 9 lb of hay dry matter, we feed 10 lb of hay.  We do put intake recommendations in amount of dry matter, so knowing how to switch between DM and As Fed is important.

Nutrient content of samples submitted to a laboratory, e.g. equi-analytical, is reported on a DM basis.  A feed tag from a commercial feed or supplement is expressed As Fed.  To determine the total intake of a given nutrient in the horse’s diet when being fed commercial feeds or supplements and hay/pasture the nutrients must be on the same terms.

Water (moisture) dilutes the nutrient content of the feed.  Based on this, a nutrient in the As Fed sample will be smaller than that reported as DM.  Basically, reporting on a DM basis is concentrating the nutrient.

Here are some examples converting from DM to As Fed and vice versa.

• Hay analysis reports crude protein (CP) as 20 % and 90% DM. What is the CP on an As Fed basis?  First, the As Fed CP will be less than 20% because it will be diluted by water.  Two options in calculating this would be to divide or multiply these two numbers.  If we divide 20% by .9 (90%DM) then we get 22.2% CP which is greater than the original amount, so that is incorrect.  If we multiple 20% by .9 (90%) we get 18% which is correct since it is less than 20%.
• Grass pasture analysis showed CP of 5% As Fed and 25% DM. At first glance the protein content looks very low and would not meet the requirement of any class of horses.  We need to put this on a DM basis in order to better understand how it relates to other feeds, e.g. hay.  Since the nutrients in As Fed are diluted by water, the answer in DM will be greater than that in the As Fed report.  We can divide or multiply the %CP by %DM.  Using division, we get 5% divided by .25 (25%DM) equals 20% CP.  Multiplying 5% by .25 (25%DM) results in a CP content of 1.25% which is lower than the undiluted results, which is incorrect.
• Most nutritionist will recommend feeding a minimum of 1% of a horse’s body weight on a DM basis. That equates to 10 lb. DM.  How much hay would you feed to accomplish this?  The hay being fed is 90% DM.  Since the hay will be diluted, the amount of hay being fed will be greater than 10 lb., so you would divide: 10 lb. / .9 (90%DM).  You would feed 11 lb. of hay.
• A commercial feed guarantees 16% CP. Knowing feed tags report nutrient content in As Fed and most feeds will average 90% DM we can determine the amount of CP in the feed on a DM basis.  Will the %CP be greater or less than the amount on the tag?  Since its diluted with water, removing the water will result in greater %CP.  If we use division, we would divide 16 % by .9 (90% DM) and get 17.7% CP, multiplying shows CP at 14.4% which is less than the original content.

Please let me know if this is confusing or if you have questions.  You can send emails to me at [email protected]. In the future we will discuss how to put this into practice when feeding your horse.

Thanks.