As Fed or Dry Matter: Understand Which to Read on Your Hay Analysis.
By: Paul Sirois, MS, PAS – Manager – Equi-analytical/Dairy One Laboratories
You’ve heard that having your hay or pasture analyzed is critical to determining how well you’re meeting your horse’s daily nutrient needs. You diligently spent time collecting your sample to ensure that it is representative, *you sent it off to the lab, and now you’ve received your results. The page is full of numbers expressed as percentages, parts per million (ppm), grams/lb., etc. Additionally, there are at least two columns of numbers – one labeled “As Fed or As Sampled” and the other “Dry Matter or DM basis”.
Most people are apt to look at the “As Fed” fed column reasoning that “I’m feeding my horse, thus the ‘as fed’ values are the ones that I want”. In reality, the numbers in the “DM column” are of the greatest value. Therefore, to properly interpret your forage analysis report, you must first understand the meaning of the two columns.
All feeds and forages are made up of two basic components – water (or moisture) and dry matter (everything that is not water). The dry matter is composed of protein, carbohydrates, minerals, etc. and defines the nutrient value of the forage. Thus, it is the composition of the dry matter that will determine the nutrient contribution to the diet and how close the forage comes to meeting your horse’s daily requirements.
Reporting results on a 100% dry matter basis removes the dilution effect of the water on the results and this is best illustrated by using an example. Examine the case of hay vs. pasture in the table below.
Table 1. As Fed vs. 100% Dry Matter results
% Crude Protein
As Fed DM basis
Hay (90% dry matter) 14.4 16.0
Pasture (20% dry matter) 4.0 20.0
Hay is typically 90% dry matter (10% moisture) and pasture almost the complete opposite at 20% dry matter (80% moisture). If you just considered the As Fed results, you’d assume that the hay is better in quality. However, once you remove the moisture, the pasture has a higher protein content per pound of dry matter – and it is the dry matter that supplies the nutrients. Hence, eliminating the dilution effect of the water allows you to make an “apples to apples” comparison of the nutrient values. The tradeoff is that the horse will have to consume more pounds of pasture to meet its daily nutrient needs. Continuing the example, if a horse consumes 10 lbs. of hay, this is equal to 9 lbs of dry matter (10 x (90/100)). To consume the same amount of dry matter from pasture, the horse will need to consume 45 lbs of pasture (9/(20/100)). To think of it in a different way, 10 lbs. of hay is composed of 9 lbs. of dry matter and 1 lb. of water. Likewise, 45 lbs. of pasture is composed of 9 lbs. of dry matter and 36 lbs. of water.
The National Research Council (NRC) generates publications of nutrient requirement tables for most classes of domestic livestock. The tables outline daily nutrient needs based on growth, daily activity, reproductive state, etc. These tables form the foundation for most ration programs used by nutritionists to develop balanced rations for their clients. All of the values in these tables are expressed on a dry matter basis. Nutritionists use this information in conjunction with the dry matter values on your report to develop sound, balanced rations for your horses.
In summary, all forage and feeds are composed of two basic fractions: water (moisture) and dry matter (everything else). Daily requirements are based on the consumption of nutrients in the dry matter. Requirements are expressed on a dry matter basis and logically, forage analysis results should be used on a dry matter basis for developing rations and comparing different feeds. Grasping this basic concept is the first step to understanding nutrient requirements and interpreting analytical results. You’ve now got an essential tool for understanding, evaluating, and developing well-formulated diets.
*Wondering what nutrient combinations you can test for? Check out the Equi-Analytical packages available for purchase here.