Steve Boyles, OSU Beef Extension Specialist

Properly interpreting a forage sample analysis report may be the most important thing you can do for your cows this winter!

Previous articles in this publication have established the critical need for forage analysis on the various timings and cuttings of forages that have been made throughout Ohio this year. Once the forage analysis report is received back from the laboratory, the information below will help with interpretation of the results.

Dry matter (DM) is the percentage of feed that is not water.  Dry matter basis allow you to compare feeds such as hay, grain and silage.  Many software packages formulate diets on the dry matter basis.  Feed test results may have dry matter and “as fed” values.  As fed is the nutrient content with the water included.  You will note that the dry matter values are higher than the as fed values.  Removing the water makes the nutrient values to be higher or more concentrated.

Crude protein (CP) measures both true protein and non-protein nitrogen. Crude protein is an excellent place to start but some other values or ways to evaluate protein exist.

Insoluble crude protein (ICP), acid detergent insoluble nitrogen (ADIN), unavailable nitrogen, and heat-damaged protein all refer to nitrogen (or CP) that has become chemically linked to carbohydrates to form an indigestible compound.  The overheating that causes this reaction is most common in silage stored at less than 65 percent moisture and in hay stored above 20 percent moisture.  Available or Adjusted crude protein (ACP) is a value corrected for heat damage. It should be used in place of crude protein.

Protein requirements are now including metabolizable protein (MP) so as to take into consideration the differences in rates of digestion and utilization of various protein sources and to account for requirements of rumen bacteria and those of the animal. This is a change over the established system of describing protein requirements as Crude Protein.  While energy is the most commonly deficient nutrient in beef-cow diets, protein often represents the largest “out-of-pocket” expense.  Protein can be divided into two components, degradable intake protein (DIP) and undegradable intake protein (UIP). The DIP fraction is available to the rumen microflora and can be used for their growth and digestion of dietary fiber. Supplementing low-quality forages with DIP has been shown to increase forage digestion and intake. The UIP is not available to the rumen microflora and has no effect on forage utilization. The UIP fraction can be a direct supply of amino acids to the cow or it can go undigested and be expelled.

Oil seed byproducts (soybean meal, cottonseed meal, sunflower meal) contain a high percentage of DIP while proteins derived from animal sources contain mostly UIP.  Forage-based diets should be focused on the inclusion rates of DIP in the diet.

Generally, DIP can supply CP approximately 7% of the diet. If the required CP in the diet exceeds 7% of the DM, all CP above this amount should be UIP. In other words, if the final diet is to contain 13% CP, 7 of the 13 units should be UIP, or 54% of the CP and 6 of the 13 percentage units should be DIP, or 46% of the CP.

Crude fiber (CF) is an old, well-known fiber determination. Newer fiber methods are more useful measures of nutritional value.

Neutral detergent fiber (NDF) measures the structural part of the plant, the plant cell wall. NDF gives “bulk” or “fill” to the diet.  Therefore lower numbers indicate higher quality and intake potential.

Acid detergent fiber (ADF) primarily consists of cellulose, lignin, silica, insoluble crude protein and ash, which are the least digestible parts of the plant. Low ADF is preferred because if means higher energy.

Total digestible nutrients (TDN) represents the total of the digestible components of crude fiber, protein, fat, and nitrogen-free extract in the diet. It is less accurate than Net Energy (NE) for formulating diets containing both forage and grain.  However, it can still be used for developing cow diets.  Some older ration balancing software packages use TDN.

Net energy (NE) The net energy value of a feed depends on whether the feed is used for maintenance (NE_m), producing weight gain (NE_g), or milk production (NE_l).  Beef cattle diets are developed based on net energy maintenance and gain vales.  Net energy lactation values are used for dairy cows/diets.  Ether Extract can be of interest if you are using feeds high in fat/oils.

Many feed analysis sheet provide valuable information on minerals such as calcium, phosphorus, copper, magnesium, potassium and zinc.  Typically, if you are interested in selenium, that is another test/cost.

With this analysis you can work with your local feed company representatives or university extension personnel.  There are ration balancing software packages available as well.  However, if you do not understand ruminant nutrition, software just gets you into trouble faster than pencil, paper and calculator.

References:

Little, C. 2008. Forage testing for beef cattle. OSU Extension. ANR-002-98.

Owen, F., B. Anderson, R. Rasby and T. Madder. 1989. Testing livestock feed. Nebguide. G89-915