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Does it really matter how we sample forages for testing? Does sampling method affect the results?

Posted by jhheiss | August 2, 2022

Beef Cattle Mythbuster
Understanding forage testing and interpretation of results

 Dr. Don Llewellyn, Director, Lincoln County WSU Extension, Davenport, WA

 Does it really matter how we sample forages for testing?  Does sampling method affect the results?

 Answer:  Yes!

Well haying season is under way, and it appears that as far as weather goes, there have been some challenges.  I’ve been around this great land we call the USA quite a bit and I’ve seen hay from a good many places.  I can tell you with confidence that the hay raised in Eastern Washington is as good as it gets.  However, there still is variation from year to year, species to species, and cutting to cutting.  This month, let’s take a look at forage testing, how it’s done, and how to interpret the report.

Most producers pay close attention to the physical characteristics of their forage when determining quality, but from a nutritional standpoint, the quality of a forage is reflected in its chemical composition. Understanding chemical composition allows producers to determine which forages are sufficient enough to meet their production goals. Knowing the chemical composition will also assist producers in correcting for nutrient imbalances in their cattle.

This month’s column fits nicely with a recent Beef Cattle Mythbuster where we discussed the different options for lab analysis (i.e., wet chemistry vs. NIRS).

 

Forage Sampling

When using forage testing, it is essential to send representative samples to the laboratory and to use a laboratory that is certified by The National Forage Testing Association (NFTA). Using a NFTA-certified laboratory will ensure accurate test results using recognized reference methods. Identification of the lot of hay is also very important.  A lot is comprised of hay from a particular field, cutting, species, variety, maturity and was harvested under similar conditions (i.e. weather and other environmental factors; inside vs. outside storage).  A representative sample must also be collected in order to account for the amount of variation within a lot. Hay quality changes in the stack over time, so it is important to sample the hay close to the time of feeding to ensure that the actual quality is the same as the quality reflected in the analysis. Sending flakes of hay or grab samples is not sufficient to obtain accurate and useful results. Hay-probing devices are available from several manufacturers.  Pictures and descriptions of hay probes can be found at: (https://www.foragetesting.org/hay-probes) and should be employed to sample deeper into the layers of the bales. In general, a minimum of 20 core samples per lot should be collected from as many areas in the stack as possible. For large square bales, two or three samples per bale should be sufficient. For both large and small square bales, sample from the ends between the strings. For large round bales, the probe should be inserted from the side and directed toward the center of the bale. Sampling to a depth of 12 to 24 inches, and provide a sample of approximately 200 g for analysis. It is recommended that a probe 14 to 24 inches long with a diameter of 3/8 to 5/8 inches be used. Once the samples have been collected, the material should be sealed in a plastic bag and stored in a cool place. Deliver the samples to the laboratory as soon as practical.

At times it is advisable to measure the quality of standing forage. While sampling methods are somewhat different, standing forage samples can be submitted to a laboratory like harvested hay samples.  A minimum of 20 forage clippings per pasture collected in a grid pattern works effectively. Cattle select a diet that they find most palatable, and this should be taken into account when sampling. Clip the standing forage at each site to the approximate grazing level (not less than around 4 inches). The samples can be delivered immediately to the laboratory, refrigerated or frozen, or they can be dried at 140°F to stabilize them for storage. If the weather is particularly warm, place the samples in a portable cooler to prevent deterioration.

Detailed information about forage sampling can be found on the National Forage Testing Association website at http://www.foragetesting.org/

 

Interpretation of Forage Analysis Results

Focusing on a few key forage components will give producers sufficient information to determine the usefulness of forages for beef cows and to provide a balanced feeding program. Forage analysis commonly report crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), total digestible nutrients (TDN), estimates of net energy (NE; for maintenance, growth, or lactation), and mineral composition. Analysis to determine dry matter (DM) content is also useful when comparing feeds with differing moisture contents and is especially useful when comparing feeds with high moisture content, such as silage and immature forages. Forage analysis also provides useful information on antiquality components, such as lignin, which have beneficial protective and structural roles in plants, but can negatively affect digestion and utilization of forage by beef cattle.

Generally, feed CP is quantified by determining its nitrogen (N) content. The CP content can be calculated using the equation:  %CP = %N x 6.25, assuming that amino acids (i.e., the building blocks of protein) contain approximately 16% N. Because feeds contain small amounts of non-protein nitrogen from other chemical constituents (i.e., components from cell nuclei, such as DNA and RNA), these sources are included in the final CP content. Protein that is broken down by the microbial population in a cow’s rumen becomes a source of nitrogen that can be used by rumen microbes to carry out important digestive and metabolic activities. Nitrogen from protein can be converted to ammonia and used by the rumen microbes to make microbial protein, which eventually becomes nutritionally available to the animal. In general, ammonia is the preferred nitrogen source for rumen bacteria that digest the fibrous components of forages.

When feeding low-quality forages, protein is commonly regarded as the first-limiting nutrient. This means that when protein is not present in sufficient quantities in a feed, maximizing beef cattle performance cannot occur, even if all the other essential nutrients are present in adequate amounts. Some of the nutritional aspects of protein are not reflected in CP alone. In beef cattle nutrition, protein can be divided into two categories. Ruminally degradable protein (RDP), also known as degradable intake protein (DIP), refers to that proportion of the CP that is used in the cow’s rumen for the benefit of the rumen microbes. Protein is synthesized by the rumen microbes using N derived from protein in the animal’s diet. Eventually, as the rumen microbes die off and move out of the rumen, the microbial protein is available for digestion in the small intestine. Ruminally undegradable protein (RUP), also known as undegraded intake protein (UIP), is that portion of the CP that escapes rumen degradation and is eventually digested in the small intestine. RUP or UIP is sometimes referred to as rumen bypass or escape protein. The relative degradability of feedstuffs in the rumen varies by type of feed and can be affected by feed processing or under conditions that may cause heating of the feed. Unlike animals with simple stomachs, the required metabolizable protein (MP), or true protein, absorbed by the intestine of beef cattle is met in two ways—by microbial protein and by dietary escape protein (NRC 2000). The digestibility of microbial and escape protein is a factor that helps determine the amount of protein that is ultimately absorbed by the animal.

Neutral detergent fiber (NDF) and acid detergent fiber (ADF) are measures of a forage’s fiber content. The NDF fraction contains hemicelluloses, cellulose, and lignin, while the ADF fraction contains only cellulose and lignin. Depending on the method of reporting, test results may or may not include the residual ash (mineral) content of the forage. In terms of forage quality, increases in NDF and ADF are most often negatively correlated with the CP. NDF and ADF values reflect forage intake, digestion, and utilization, and as their concentrations in a forage increase, intake and digestion decrease.

While originally calculated using digestibility coefficients from proximate analysis of feeds, TDN values may also be calculated by employing empirically derived prediction equations using the ADF analysis. This is the method used for most feed analyses. It is important to note that TDN values are estimates of organic matter (OM) digestion and only account for fecal losses, whereas the more complex system of Net Energy NE values account for energy losses incurred during the entire digestive processes. Furthermore, NE values in forage analysis reports can be obtained by using the TDN values. The negative relationships between dry matter intake and NDF, and between ADF and dry matter digestibility provide additional information about forage.

Macro- and microminerals are essential for many metabolic and life-sustaining processes in beef cattle, and they affect bone formation, hormone components and secretion, enzyme components and activators, water balance, amino acid components, glucose tolerance, components of vitamins, and antioxidation. There are at least 17 minerals that beef cattle are known to require (NRC 2000). Meeting these mineral needs requires an initial accounting of the minerals supplied by the available forage, followed by a determination of which minerals need to be supplemented. The practice of mineral supplementation is common on most beef cattle operations.

Specialized tests such as nitrate or prussic acid may be needed for forages under high nitrogen fertilization, following drought, and when feeding forages that often accumulate high levels of nitrate (i.e. sorghum x sudan hybrids).  It may also be advisable to analyze corn forages such as corn silage and stalks for mycotoxins (toxins that come from mold).

Forage analysis is an important tool for beef producers in allowing them to understand what is contained in the forage so that informed decisions can be made about meeting their cows’ nutrient requirements and to correct for imbalances with supplements if needed.

There you have it, there is no mystery about the great value of the method of sampling and interpreting the results of your forage analysis. Have a great summer!  If I can help you with your cattle and forages, give us a call we are here to help!  Don Llewellyn, Director, Lincoln County Extension, 509-725-4171, don.llewellyn@wsu.edu

 

Literature resources

NRC. 2000. Nutrient requirements of beef cattle. 7th Revised Ed., Update 2000. National Academy Press. Washington, D.C.