Time and time again we have discussed the importance of testing stored forages and pastures to determine the nutrient content of the material to be consumed by the cow. The statement is typically made that this is the only way to effectively determine what you have in the component that makes up the largest portion of the cow's diet. Forage testing allows us to: (1) balance rations, reducing costs and improving overall nutritional plane the herd is on, (2) improve future crop management if present forage is of unsatisfactory quality, and (3) determine equitable prices for feedstuffs based on nutritive value.
Unfortunately, understanding the information that is provided in the forage assay received from a given lab can sometimes be difficult, especially to those producers who are new to the process. This month's article will hopefully help clear some of the fog and help you better understand the information you receive when testing your pastures and forages. We'll discuss initially how to take a good sample to insure that your test is representative and accurate and how to best prepare samples for testing. Later we'll evaluate the information you receive on a forage testing report and what it means. Finally, we'll discuss the differences between labs and how to select a lab that best suits your needs
Sampling Techniques are Important to Accurate, Representative Assays
Taking quality forage samples takes time and planning. Consider this example: in a given cut of hay on a given field, you may make a hundred rolls, each weighing 1,200 lbs. or more. This field may be on a hill or it may contain varying soil types, Initially, this means that from this particular field you are producing a minimum of 120,000 lbs. of hay or more, enough to feed 50 cows two to three months. Additionally, you make two or more cuttings of hay from this field as well, increasing the hay stores you have available for feeding or for sale. Many producers will attempt to sample a few bales and use this to provide the information they need to plan the rest of the feeding season. The information gained from one or two samples may be sketchy at best. Following the steps below will help you insure the samples you take are a good representation of the forages you are putting up. Some of these steps take place before sampling actually takes place.
1) Group hay cuttings together so they can be easily distinguished. In other words, if stacking outside or in a barn, keep all the hay from a given cutting more or less in one place. If necessary, identify where the group stops and starts. A given cutting from a given field needs to be grouped in a specific area so you can modify your supplementation program as you change feeding from one group to another. Also, if possible, group bales from specific parts of a given field that may have distinctive or different soil characteristics. In other words, if a given field has a section that is very sandy and another that is more clay-based, try to separate these groups of hay. Also, document or map where your groups are positioned to help you remember what is where.
2) Prepare in advance by having the correct tools. You will need a forage probe, pen and paper, clean cardboard box, zip-lock bags and a permanent marker. Several different forage probes exist on the market, each designed to take a ¾ to 1 inch core, approximately 12 to 18” into a bale. Probe types include those which can be “drilled” in using a brace or a cordless drill, those which are driven in using a mallet or hammer, etc. The type I use is slightly smaller in diameter and is attached to a 2” PVC handle. The probe itself is very sharp and is easily forced directly into the bale. What I like about this particular model is not only the ease of use but the fact that I can sample four to five bales in the time it takes to sample one using typical brace and bit type probes. Quality probes can be purchased from different suppliers and range in price from $75 to $125. In many cases you can borrow a probe from the local extension office.
3) Sample each cutting of hay shortly after it is baled. I like to sample at least 10 percent of the bales in a given cutting or group of no more than 80 to 100 bales. Normally it works best when the hay has been moved in to place in your hay trap or in the barn. At this point go though and randomly sample 10 percent of the bales. After each bale is probed, empty the sample into the cardboard box. Once all the samples have been obtained, thoroughly mix the samples and remove enough to fill a quart-sized zip-lock bag ½ to ¾ of the way full. Force as much air out of the bag as possible and seal. Label the sample with the permanent marker listing your name, the date, location and cutting. Once all your samples have been collected in this manner they can be placed in a large envelope or small box for shipment to the lab.
4) With your samples, send along a cover letter listing your name and address along with a list of the samples you are including and include for each sample the same data as written on the sample bag. This simply helps the lab keep track of your samples.
5) Depending on the lab you use, your test results may take ten days to two weeks to get to you from the day you mail them. Once you receive these results, closely evaluate the data (we'll get to that in a bit). From this information you can determine which forage is of better quality and which hay needs to be fed to given groups of cows at any given point in time. This also tells you that when you start feeding a different grouping or cutting of hay you may have to increase or decrease supplementation.
The Lab Report
Reports from various labs look fairly different although they contain more or less the same information. A typical lab report may look like the following chart.
We'll take a moment and go through each of the components in this example.
Results of analysis are expressed on an "as-fed" and on a "100% dry matter (DM)" basis. The as-fed (sometimes stated “as-received”) basis includes the water or moisture the forage sample contains. Nutrients expressed on this basis represent the nutrient content of the feed when it was received at the lab. Dry matter basis means all moisture has been removed. When the moisture content of a sample is removed, this mathematically adjusts all nutrient levels higher. The nutrient concentration is that which is contained in the dry matter portion of the sample.
Components in the analysis include:
· Moisture. Moisture is the amount of water in the feed. Percent moisture = 100 - % DM.
· Dry Matter (DM). Dry matter is the amount of dry matter in the feed. It is the percentage of feed that is not water. Percent DM = 100 - % moisture. A sample of hay with 85 percent dry matter contains 15 percent water.
· Crude Protein (CP). Crude protein is termed "crude" because it is not a direct measurement of protein but a measurement of the total nitrogen in the feed. Protein is approximately 16 percent nitrogen (N). When testing a sample, the N content is determined and then multiplied by a factor of 6.25 to get the protein content. Crude protein includes true protein and non-protein nitrogen (NPN) such as urea nitrogen and ammonia nitrogen. The crude protein value provides no information about amino acid composition, availability of protein, or the amount which will bypass the rumen.
· Adjusted Crude Protein (ACP). While not shown in the example above adjusted crude protein is the amount of crude protein after correction for bound protein. Bound protein is the protein which is attached to certain fiber components which make that portion of protein indigestible.
· Acid Detergent Fiber (ADF). ADF consists primarily of cellulose, lignin, and acid detergent fiber crude protein. It is closely related to indigestibility of forages and is the major factor in calculating energy content of feeds. The lower the ADF the more energy the feed contains and the more digestible it will be.
· Neutral Detergent Fiber (NDF). The total fiber content of a forage is contained in the NDF or cell wall. This fraction contains cellulose, hemicellulose, lignin, and acid detergent crude protein. NDF gives the best estimate of the total fiber content of a feed and is closely related to feed intake. As NDF values increase, total feed intake will decrease. Grasses will contain more NDF than legumes at a comparable stage of maturity.
· Net Energy for Lactation (NEl). Net energy for lactation or (NEl) is the term used by the NRC (National Research Council) for assessing the energy requirements and feed values for lactating cows. NEl is usually expressed as megacalories per pound (Mcal/lb) or megacalories per kilogram (Mcal/kg). These units are more commonly used for assessing the energy needs of dairy cattle.
· Net Energy for Maintenance (NEm) and Net Energy for Gain (NEg). The net energy system used by NRC for beef cattle assigns two energy values (NEm and NEg) to each forage or feedstuff and similarly subdivides animal requirements for energy. NEm is the net energy value of feeds for maintenance. NEg is the net energy value of feeds for the deposition of body tissue, growth, or gain. Both NEm and NEg are needed to express the total energy needs of growing cattle. They are usually expressed as megacalories per pound (Mcal/lb).
· Total Digestible Nutrients (TDN). TDN represents the sum of digestible crude protein, digestible carbohydrates and digestible fat. Fat is multiplied by 2.25 to compensate for its higher energy content. Since feeds are utilized differently by different species, percent TDN on a feed is different for each species.
· Minerals. Calcium (Ca), phosphorus (P), magnesium (Mg), and potassium (K) values are expressed as a percentage of each in the feed. Trace minerals are typically expressed in parts per million (PPM). Other units which you may see are milligrams per kilogram (same a PPM), milligrams per lb. or in percent.
In the next issue we'll continue our discussion of understanding these assesses as well as other information that can be determined. At this time we'll also look at different types of labs and what to look for when choosing a facility.
Dr. Steve Blezinger is a nutritional and management consultant with an office in Sulphur Springs, Texas. He can be contacted at P. O. Box 653 Sulphur Springs, TX 78543, by phone at (903) 885-7992 or by e-mail at email@example.com.