# Understanding Forage Quality Testing for Dairy Rations ## Key Takeaways - Forage quality testing is critical for dairy ration formulation, measuring parameters like Dry Matter (DM), Crude Protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), and energy estimates (TDN, NEL). Accurate DM measurement is foundational, as all other nutrient calculations are based on it, and significant shifts (3-5%) necessitate ration adjustments. - NDF is the primary predictor of forage intake potential, with higher NDF limiting dry matter consumption due to rumen fill; ADF is used to estimate energy content, as increasing ADF reduces digestibility. Legumes generally have a lower NDF:ADF ratio than grasses, indicating higher intake potential for a given NDF level. - Proper sampling is paramount: use a probe for hay, collecting cores from 10-20 bales per lot, and sample silage from the face after fermentation is complete (3-4 weeks post-ensiling), discarding the outer 6 inches and collecting from multiple depths. - Regular testing is essential: sample every cutting or lot before feeding, and retest silage every 2-4 weeks during feeding to account for DM changes at the feedout face. - Key decision thresholds include maintaining forage NDF below 45% for legumes and 55% for grasses for lactating cows to support intake, and ensuring total ration NDF is 28-32%. For dry cows, total ration NDF should be 35-40% for rumen fill. - Mineral analysis, particularly calcium, phosphorus, potassium, and magnesium, is vital for preventing metabolic disorders; high potassium (>3% in forage) is problematic for dry cows, potentially interfering with magnesium absorption and increasing the risk of grass tetany. --- Forage quality testing is one of the most important management tools available to dairy farmers, yet many operations underuse it or misinterpret the results. This guide explains what forage testing measures, why those measurements matter for milk production and herd health, and how to sample, interpret, and apply test results to build better rations. It is written for dairy producers, herd managers, nutritionists, and anyone who buys or sells hay and silage for dairy cattle. ## At a Glance | Topic | Key Takeaway | |---|---| | What forage testing measures | Dry matter, crude protein, NDF, ADF, lignin, minerals, and energy estimates like TDN and NEL | | Why it matters | Rations built on tested forage are more accurate, cheaper, and support higher milk production with fewer health problems | | Sampling basics | Use a probe for hay, collect cores from multiple bales, and sample silage from the face after fermentation is complete | | When to test | Every cutting or lot, before feeding a new batch, and when you notice changes in intake or milk production | | Common mistakes | Testing too few samples, sampling spoiled forage, waiting too long to use results, and ignoring moisture changes | | Decision thresholds | Use NDF to balance intake, ADF to predict energy, and CP to balance protein. Adjust rations when dry matter shifts by more than 3 to 5 units | | Recordkeeping | Keep a forage inventory log with test dates, lab results, and ration changes for every cutting and storage structure | | When to get help | Call a nutritionist for ration balancing and an extension agent or veterinarian if you suspect mycotoxins or a nutritional disorder | ## Why Forage Quality Testing Matters for Dairy Herds Forage is the foundation of the dairy ration. On most farms, it supplies 50 to 70 percent of the dry matter that lactating cows consume. When you know exactly what is in that forage, you can build a ration that meets the cow's needs without overfeeding expensive supplements or underfeeding the nutrients she requires for milk production. The problem is that forage quality varies widely. The same field can produce hay or silage with very different nutrient content depending on the maturity at harvest, the weather during curing, the storage method, and the length of time the forage has been stored. Two cuttings taken three weeks apart can differ by 5 or more points of crude protein and by 10 or more points of NDF. Without a test, you are guessing, and guessing is expensive. Forage testing removes the guesswork. It lets you compare the actual value of what you grew against what the cow needs. It also helps you make better decisions about what to buy. If you are shopping for hay, a test report tells you whether the seller's price is fair for the nutrient content. If you are selling hay, a test report justifies a higher price for better quality. Testing also protects herd health. Forages that are too high in fiber limit dry matter intake, which means the cow cannot eat enough energy to support milk production. Forages that are too low in fiber can cause acidosis. Forages with the wrong mineral balance can contribute to milk fever, grass tetany, or other metabolic disorders. Testing gives you the information you need to prevent these problems before they show up in the tank or the treatment pen. ## What a Forage Test Measures A standard forage test from a commercial laboratory reports several key values. Understanding what each one means is essential for using the results correctly. ### Dry Matter Dry matter is the percentage of the sample that is not water. Fresh grass might be 20 percent dry matter, while dry hay is usually 88 to 92 percent dry matter. Silage typically runs 30 to 45 percent dry matter depending on the crop and harvest method. Dry matter matters for two reasons. First, it tells you how much water you are hauling and storing. Second, it is the basis for all other nutrient calculations. When you balance a ration, you work in pounds of dry matter, not pounds of as-fed feed. If you do not know the dry matter, you cannot know how many pounds of actual feed you are putting in front of the cow. Dry matter changes over time. Silage loses moisture as it ferments and as it is exposed to air at the feedout face. Hay continues to lose or gain moisture depending on the humidity. This means the dry matter you measured at harvest is not the dry matter you are feeding six weeks later. You need to monitor dry matter regularly, especially with silage. ### Crude Protein Crude protein is an estimate of the total protein in the forage. It is calculated by measuring the nitrogen content and multiplying by 6.25. This value includes both true protein and nonprotein nitrogen. Forage crude protein varies widely. Legumes like alfalfa often test 18 to 24 percent crude protein. Cool-season grasses run 10 to 18 percent depending on maturity. Corn silage is usually 7 to 9 percent crude protein. Crude protein is important for balancing the protein portion of the ration, but it is not the whole story. The cow also needs to know how much of that protein will be degraded in the rumen and how much will pass through to the small intestine. Some labs report additional protein fractions that help your nutritionist make more precise decisions. At a minimum, the crude protein value tells you whether the forage is a protein source or an energy source in your feeding program. ### NDF and ADF Neutral detergent fiber and acid detergent fiber are the two most important fiber measurements in forage testing. NDF measures the total cell wall content of the plant. This includes cellulose, hemicellulose, and lignin. NDF is the best single predictor of how much forage a cow can eat. As NDF increases, dry matter intake decreases because the cow's rumen fills up and the fiber takes longer to digest. High-quality legumes might have 30 to 35 percent NDF, while mature grass hay can exceed 60 percent NDF. ADF measures the cellulose and lignin portion of the fiber. It is used to estimate digestibility and energy content. As ADF increases, digestibility decreases. High-quality alfalfa might have 25 to 30 percent ADF, while stemmy, mature hay can have 40 percent or more. The relationship between NDF and ADF tells you something about the type of forage. Legumes have a lower NDF to ADF ratio than grasses. This means legumes can support higher intake for a given NDF level, which is one reason alfalfa is such a valuable dairy forage. ### Lignin Lignin is the indigestible part of the plant cell wall. It is included in both NDF and ADF, but it deserves separate attention because it is the main factor limiting fiber digestibility. As plants mature, lignin content increases and the fiber becomes less digestible. Some labs report lignin as a percentage of the sample or as a percentage of NDF. Higher lignin means lower energy availability. This value is especially useful for comparing forages from different harvest dates or for evaluating the potential of brown midrib varieties. ### Energy Estimates Energy is not measured directly in a forage test. Instead, it is calculated from the fiber and other components. The most common energy values reported are: Total digestible nutrients is an estimate of the total digestible nutrient content of the feed. It is calculated from ADF or from a summative equation that uses multiple components. Net energy for lactation is the energy value of the feed that is actually available for milk production after accounting for energy lost in feces, urine, gas, and heat. NEL is calculated from TDN and is the value most nutritionists use when balancing rations. Energy values decrease as fiber and lignin increase. High-quality alfalfa hay might have a TDN of 60 to 62 percent and an NEL of 0.60 to 0.64 Mcal per pound of dry matter. Mature grass hay might have a TDN of 50 percent or less and an NEL below 0.50. ### Minerals Most standard forage tests include calcium, phosphorus, potassium, and magnesium. Some also include sulfur, sodium, and trace minerals. Calcium and phosphorus are important for bone health and milk production. The calcium to phosphorus ratio in the total ration should be roughly 1.5 to 2 to 1. High-calcium forages like alfalfa can help you meet the cow's calcium needs, but they also require careful attention to the phosphorus balance. Potassium is often high in forages, especially those grown on manured ground. High potassium levels can interfere with magnesium absorption and contribute to grass tetany in dry cows. This is why dry cow rations often need to limit high-potassium forages. Magnesium is important for nerve and muscle function. Low magnesium in the forage combined with high potassium can trigger grass tetany, especially in early lactation. ### Relative Feed Value and Relative Forage Quality Many labs report a single index number to help you compare forages. Relative feed value is calculated from NDF and ADF. Relative forage quality is a newer index that also accounts for fiber digestibility. These indexes are useful for comparing forages within a class, but they have limitations. They work best for comparing legumes to legumes or grasses to grasses. They do not account for differences in protein, minerals, or the digestibility of the nonfiber components. Use them as a screening tool, not as the final word on forage value. ## How to Sample Forage Correctly The best lab in the country cannot fix a bad sample. Sampling errors are the most common source of inaccurate forage test results. Follow these procedures to get a representative sample. ### Sampling Hay Use a hay probe, not your hands. A hay probe is a hollow metal tube that you drive into the bale to collect a core sample. Hand-pulled samples only collect the outside of the bale, which has different nutrient content than the inside. Collect cores from at least 10 to 20 bales for a lot of hay. A lot is hay that was cut from the same field, at the same maturity, and harvested under the same conditions. If you have 100 bales that all came from one cutting, sample 15 to 20 of them. If you have a mixed lot, sort the bales by visual appearance first and sample each group separately. Push the probe into the end of the bale, not the side. The end gives you a core through the full width of the bale, which captures the variation from the outside to the inside. Take one core from the center and several from the midpoints between the center and the edges. Combine the cores from all the bales into one clean plastic bucket. Mix them thoroughly, then fill a sample bag with about one pint of the composite. Seal the bag, label it with the date and a description of the lot, and send it to the lab the same day. Never sample moldy or spoiled hay unless you are trying to determine whether it is safe to feed. A test of spoiled hay will not tell you the quality of the good hay in the same lot. Sample the good hay separately and evaluate the spoiled hay separately. ### Sampling Silage Silage sampling is more complex than hay sampling because the [fermentation process](/knowledge/molecular-biology/fermentation-process) changes the nutrient content over time. The first step is to wait until fermentation is complete. This takes at least three to four weeks after the silo is sealed. Sampling earlier gives you results that do not match what you will actually feed. At the feedout face, collect samples from the entire exposed surface, not just the top or the bottom. Silage separates by particle size and density as it is packed, so the face can vary from top to bottom. Use a clean shovel or a specialized silage sampler to collect material from the top, middle, and bottom of the face. Discard the outer 6 inches of the face before sampling. This material has been exposed to air and has lost moisture and quality. You want to sample the silage that the cow will actually eat, not the spoiled outer layer. Collect at least 12 to 15 handfuls from different locations across the face. Combine them in a bucket, mix well, and fill a sample bag. If the silage is very wet, squeeze the bag to remove excess moisture before sealing. Freeze the sample if you cannot send it to the lab within a day. For silage bags or piles, sample from multiple access points. For upright silos, sample after the silage has been fed down at least a foot to expose a fresh surface. ### Sampling Haylage and Baled Silage Haylage and baled silage follow the same principles as other silage, with a few adjustments. For baled silage, use a hay probe to collect cores from multiple bales, just as you would for dry hay. Sample at least 10 bales per lot. Combine the cores and send a composite sample. For haylage stored in an upright or bunker silo, sample from the face after fermentation is complete. The material is usually wetter than corn silage, so be careful to keep the sample cold and send it quickly to prevent spoilage during shipping. ### Sampling Frequency Sample every cutting and every lot. Do not assume that second cutting alfalfa will test the same as first cutting, even from the same field. Weather, soil moisture, and plant maturity all affect nutrient content. For silage, sample again after the silo has been open for a few weeks. The dry matter at the feedout face will be different from the dry matter at the time of harvest. This is especially true in warm weather when the face dries out quickly. Many nutritionists recommend sampling silage every two to four weeks during the feeding period. The cost of a test is small compared to the cost of feeding an unbalanced ration for a month. ## Choosing a Laboratory Forage testing laboratories are not all the same. Some specialize in feed analysis, while others are general agricultural labs. Look for a lab that uses near-infrared reflectance spectroscopy or wet chemistry methods and participates in a certification program. The National Forage Testing Association certifies labs that meet specific standards for accuracy and precision. Ask your lab whether it is certified and how often it runs check samples. A certified lab gives you more confidence that the results are reliable. Most labs offer different packages. A basic package includes dry matter, crude protein, ADF, NDF, and sometimes minerals. A more complete package adds lignin, energy estimates, and additional mineral values. Work with your nutritionist to decide which package fits your needs. Turnaround time matters. Most labs return results within three to five business days after receiving the sample. If you are about to feed a new lot of hay, you need the results before the hay reaches the feed bunk, not after. Plan your sampling schedule so that you have results before you switch feeds. ## How to Read and Interpret a Forage Test Report The numbers on a forage test report only help you if you understand what they mean for your cows. Here is how to work through a test report step by step. ### Check the Dry Matter First Before you do anything else, look at the dry matter. If the dry matter is very different from what you expected, the rest of the numbers may be misleading. For example, if you sampled hay that you thought was 90 percent dry matter and the test says 82 percent, the hay may have absorbed moisture during storage or the sample may have been taken from a damp area. Dry matter also affects how much feed you actually deliver. If the dry matter drops from 90 to 85 percent, you need to feed more as-fed pounds to deliver the same amount of dry matter. A 5 percent change in dry matter means a 5 percent change in the amount of feed you put in front of the cow. ### Compare NDF to Expected Values NDF is your first check on forage quality. Use the following general guidelines for legumes and grasses. For alfalfa and other legumes, NDF below 35 percent is excellent, 35 to 40 percent is good, 40 to 45 percent is average, and above 45 percent is poor for lactating dairy cows. For grasses, NDF below 45 percent is good, 45 to 55 percent is average, and above 55 percent is poor for high-producing cows. NDF also tells you about intake potential. A cow can consume about 1.1 to 1.2 percent of her body weight in NDF per day. A 1,400 pound cow can handle about 15 to 17 pounds of NDF per day. If your forage is 40 percent NDF and the cow eats 40 pounds of forage dry matter, she is getting 16 pounds of NDF, which is right at her limit. If the NDF is 50 percent, she will only be able to eat about 32 pounds of forage dry matter before she hits her NDF limit. ### Use ADF to Estimate Energy ADF is your best quick estimate of energy content. As ADF goes up, energy goes down. For alfalfa, ADF below 27 percent is excellent, 27 to 30 percent is good, 30 to 34 percent is average, and above 34 percent is poor. For grasses, ADF below 30 percent is good, 30 to 35 percent is average, and above 35 percent is poor. The lab will usually report TDN and NEL calculated from the ADF or from a more complex equation. Use these values to compare forages and to estimate how much grain you need to add to meet the cow's energy requirements. ### Check Protein Against Your Needs Crude protein tells you whether the forage is a protein source or an energy source. High-quality legumes can supply most of the protein a lactating cow needs. Corn silage and mature grasses are low in protein and require supplemental protein in the grain mix. Compare the crude protein to the target for your ration. If the forage is lower in protein than expected, you need to add more protein supplement. If it is higher, you can reduce the supplement and save money. ### Evaluate the Mineral Profile Minerals are easy to overlook, but they have a big impact on herd health. Check potassium first. Forages grown on manured ground often have potassium above 3 percent, which is too high for dry cows. If you are feeding this forage to dry cows, you may need to dilute it with low-potassium feeds or add anionic salts. Calcium and phosphorus should be evaluated together. The ratio matters more than the absolute values. High calcium is not a problem by itself, but high calcium with low phosphorus can create a mineral imbalance. Magnesium below 0.2 percent is a concern, especially for cows grazing or eating forage that is also high in potassium. Low magnesium can trigger grass tetany, which is a medical emergency. ## Using Forage Test Results to Balance Rations Forage test results are only useful when you act on them. The following steps show how to apply the numbers to your feeding program. ### Step 1: Determine Your Target Ration Work with your nutritionist to establish target values for the total ration. These targets depend on your herd's average milk production, stage of lactation, body condition, and the facilities you have. A ration for a 90 pound average herd looks different from a ration for a 60 pound average herd. Your target ration should specify dry matter intake, crude protein, NDF, ADF, NEL, calcium, phosphorus, potassium, and magnesium. Write these targets down so you can compare them to what the forage actually provides. ### Step 2: Calculate What the Forage Provides Using the forage test results, calculate how much of each nutrient the forage supplies at your target dry matter intake. For example, if you want the cow to eat 25 pounds of forage dry matter and the forage is 20 percent crude protein, the forage supplies 5 pounds of crude protein. Do this calculation for every nutrient in your target ration. The difference between the forage supply and the target is what you need to provide in the grain mix and supplements. ### Step 3: Adjust the Concentrate Mix Once you know what the forage provides, adjust the concentrate mix to fill the gaps. If the forage is lower in protein than expected, increase the protein supplement. If the forage is lower in energy, increase the grain or add a fat supplement. If the forage is higher in NDF, you may need to reduce forage in the ration and increase concentrates to keep intake and energy up. This is where a nutritionist earns their fee. Ration balancing software can calculate the least-cost combination of feeds that meets all the cow's requirements. Give your nutritionist the forage test results and let them build the ration. ### Step 4: Monitor Dry Matter Intake After you implement a new ration based on forage test results, watch dry matter intake closely. If intake drops, the forage may be lower in quality than the test suggested, or the ration may be out of balance. If intake rises, the forage may be better than expected, and you may be able to reduce concentrate feeding. Weigh feed refusals regularly. The difference between feed offered and feed refused tells you how much the cows actually ate. Compare this to your target intake and adjust the ration accordingly. ### Step 5: Rebalance When the Forage Changes Forage quality changes over time, even within a single storage structure. Silage at the top of a bunker may be drier and lower in quality than silage at the bottom. Hay stored in a humid barn may pick up moisture and lose dry matter. Rebalance the ration whenever you open a new silo, start a new lot of hay, or notice a change in dry matter of more than 3 to 5 percentage points. This means testing more than once per cutting for silage. ## Common Mistakes in Forage Testing Farmers make several predictable mistakes when testing forage. Avoiding these errors will save you money and prevent herd health problems. ### Testing Too Few Samples One core from one bale does not represent a whole field or a whole cutting. The variation within a field can be substantial, especially if the field has variable soil types, drainage, or fertility. Collect enough cores to capture that variation. More samples cost a little more money but save much more in avoided ration errors. ### Sampling Spoiled or Unrepresentative Material Do not sample moldy hay, spoiled silage, or the weathered outer layer of a silage face. These samples do not represent what the cows will eat. If you need to know whether spoiled feed is safe to feed, test it separately and clearly label it as spoiled. ### Using Stale Test Results A forage test is a snapshot of the forage at the time of sampling. It is not a permanent description of that feed. Silage changes as it ferments and as it is exposed to air. Hay changes with moisture conditions. If you are feeding from a silo that was opened three months ago, the test you ran at harvest is probably not accurate for what you are feeding today. ### Ignoring Dry Matter Changes Dry matter is the most dynamic value on the test report, and it has the biggest effect on your feeding program. If the dry matter changes and you do not adjust the as-fed delivery rate, you will feed too much or too little dry matter. This is a common cause of unexplained drops in milk production or increases in body condition loss. ### Confusing RFV with Quality Relative feed value is a useful index, but it is not the same as true quality. Two forages with the same RFV can have very different protein, mineral, and digestibility values. Use RFV to screen forages, but make your final decisions based on the full test report. ### Not Sharing Results with the Nutritionist Your nutritionist cannot balance a ration they cannot see. Send the test results to your nutritionist as soon as you get them. Do not wait until the feed is already in the bunk. The whole point of testing is to adjust the ration before you feed the forage, not after. ## Decision Thresholds for Forage Quality The following thresholds can help you make quick decisions about whether a forage is suitable for a particular group of cows. ### Dry Matter For hay, dry matter should be above 86 percent for safe storage. Hay below 85 percent dry matter is at risk for mold growth. For silage, dry matter should be 30 to 40 percent for corn silage and 40 to 55 percent for haylage. Silage below 30 percent dry matter has poor fermentation and produces more seepage. Silage above 55 percent dry matter may not pack well and can heat. ### Crude Protein For lactating cow rations, the total ration should be 16 to 18 percent crude protein. If your forage is below 12 percent crude protein, you will need substantial protein supplementation. If it is above 20 percent, you can reduce purchased protein. For dry cows, the total ration should be 12 to 14 percent crude protein. High protein forages can be diluted with low protein feeds or straw. ### NDF For lactating cows, the total ration should be 28 to 32 percent NDF, with at least 20 to 22 percent of that from forage. Forage NDF above 45 percent in legumes or above 55 percent in grasses will limit intake and milk production. For dry cows, the total ration should be higher in NDF, around 35 to 40 percent, to maintain rumen fill and prevent overconditioning. ### ADF For lactating cows, the total ration should be 19 to 21 percent ADF. Forage ADF above 34 percent in legumes or above 40 percent in grasses indicates poor digestibility and low energy. ### Potassium For dry cows, potassium should be below 1.5 percent of the total ration dry matter. Forages with potassium above 3 percent are problematic for dry cow rations. For lactating cows, potassium up to 1.5 to 2 percent is acceptable. ### When to Reject a Forage Reject a forage when it is moldy, spoiled, or contaminated with soil, manure, or foreign material. Reject hay that was rained on repeatedly and has lost its color and leaf content. Reject silage that smells like butyric acid, which indicates poor fermentation and low palatability. For nutrient content, reject a forage for lactating cows if the NDF is above 50 percent for legumes or above 60 percent for grasses. These forages will not support adequate intake or milk production. Use them for dry cows, heifers, or beef cattle instead. ## Monitoring and Recordkeeping Forage testing is not a one-time event. It is a continuous process that requires good records to be effective. ### Keep a Forage Inventory Log Create a simple spreadsheet or notebook that tracks every lot of forage on the farm. For each lot, record: - The field and cutting - The harvest date and weather conditions - The storage location and structure - The date the sample was taken - The lab and test package used - The complete test results - The date the forage was first fed - Any ration changes made based on the test This log helps you compare forages across years and cuttings. It also helps you identify patterns. If second cutting always tests lower in protein than first cutting on your farm, you can plan your supplement purchases accordingly. ### Track Dry Matter Over Time For silage, record the dry matter at harvest and then retest every two to four weeks during feeding. Track the dry matter changes in your log. When the dry matter shifts by more than 3 to 5 percentage points, recalculate the as-fed delivery rate and notify your nutritionist. ### Monitor Milk Production and Herd Health The ultimate test of forage quality is how the cows perform. Track milk production, milk fat and protein percentages, dry matter intake, body condition score, and health events. If milk production drops after switching to a new lot of forage, the forage quality may be lower than the test indicated. If milk fat percentage drops, the ration may be too low in effective fiber. ### Review Results with Your Nutritionist Schedule a regular review of your forage test results and herd performance with your nutritionist. This should happen at least quarterly, and more often during times of ration changes. The nutritionist can help you interpret the numbers in the context of your whole feeding program. ## When to Call a Veterinarian or Extension Agent Forage testing is a management tool, not a diagnostic tool. In most cases, you do not need a veterinarian or extension agent to interpret a forage test. But there are situations where professional help is essential. ### Suspected Mycotoxin Contamination If your forage test or your herd's behavior suggests mycotoxin contamination, call your veterinarian or extension agent immediately. Signs of mycotoxin problems include: - Sudden drops in feed intake - Reduced milk production - Increased incidence of digestive upsets - Poor immune response and more infections - Reproductive problems Standard forage tests do not screen for mycotoxins. You need a specialized test to detect these toxins. Your veterinarian or extension agent can help you decide whether mycotoxin testing is warranted and can help you interpret the results. ### Nutritional Disorders If cows develop milk fever, grass tetany, ketosis, or displaced abomasum shortly after a ration change, call your veterinarian. These conditions can be triggered by mineral imbalances or by sudden changes in forage quality. The veterinarian can treat the affected cows and help you identify the cause. ### Unexplained Poor Performance If milk production is below expectations and you cannot explain it with your forage test results, call your nutritionist first. If the nutritionist cannot find the problem, call your veterinarian. There may be a health issue that is not related to nutrition. ### Extension Agent for Sampling and Interpretation Your local extension agent can help you with sampling technique, choosing a laboratory, and interpreting test results. Extension agents often have access to local forage testing programs and can help you compare your results to regional averages. They are especially valuable if you are new to forage testing or if you are considering changing your forage management practices. ## Frequently Asked Questions ### How often should I test my forage? Test every cutting or lot before you feed it. For hay, one test per lot is usually enough unless the hay is stored for a long time and may have changed. For silage, test at harvest and then retest every two to four weeks during feeding because dry matter changes as the silage is exposed to air. ### What is the difference between NDF and ADF, and why do I need both? NDF measures the total cell wall content and predicts how much forage a cow can eat. ADF measures the less digestible portion of the fiber and predicts energy content. You need both because they affect different aspects of the ration. NDF controls intake, and ADF controls energy density. ### Can I test forage that is already spoiled? You can test spoiled forage, but the results will not tell you about the quality of the good forage in the same lot. Test spoiled forage separately if you need to know whether it is safe to feed. Your veterinarian can help you interpret the results and assess the risk of mycotoxins. ### How much does a forage test cost? A standard forage test costs roughly 20 to 40 dollars depending on the lab and the package you choose. A complete test with minerals and energy estimates costs more, usually 40 to 60 dollars. The cost is small compared to the value of accurate ration balancing. One avoided case of milk fever or one week of maintained milk production pays for many tests. ### What do I do if my forage tests lower in quality than I expected? First, check your sampling technique. If the sample was not representative, retest before making major ration changes. If the test is accurate, adjust the ration to compensate. Add more concentrates to meet energy needs, add protein supplement if protein is low, and consider whether the forage is better suited for dry cows or heifers than for lactating cows. ### How do I know if my hay probe is taking a good sample? A good hay probe should be at least 12 to 18 inches long with a sharp tip and a cutting edge. It should easily penetrate the bale and collect a core without shattering the hay. If the probe is dull or bends when you push it, replace it. Clean the probe between samples to avoid contamination. ### Should I test corn silage differently than haylage? The sampling procedure is similar, but the interpretation is different. Corn silage is lower in protein and higher in energy than haylage. Corn silage also has different fiber characteristics. Use the lab results to compare corn silage to expected values for corn silage, not to expected values for alfalfa. ### What is the best time to sample a silo? Sample after the silage has fermented for at least three to four weeks. At the feedout face, discard the outer 6 inches of spoiled material, then collect samples from the top, middle, and bottom of the face. Sample in the morning when the face is fresh, and keep the sample cold until you send it to the lab. ## Related Farming Guides This section will be populated with links to related dairy nutrition, forage management, and herd health guides. Check back for updated content on ration balancing, silage management, and metabolic disease prevention. ## Related Clinical & Scientific Guides * [Evaluating Feed Additives for Dairy Cow Performance](/knowledge/animal-farming/dairy-cattle/evaluating-feed-additives-for-dairy-cow-performance) * [Dairy Barn Fire Safety: Design and Prevention Measures](/knowledge/animal-farming/dairy-cattle/dairy-barn-fire-safety-design-prevention) * [Dairy Cow Pregnancy Loss Records and Review](/knowledge/animal-farming/dairy-cattle/dairy-cow-pregnancy-loss-records-and-review) ## References - National Mastitis Council: https://www.nmconline.org/ - USDA APHIS Dairy Cattle Health: https://www.aphis.usda.gov/livestock-poultry-disease/cattle - FAO Dairy Production and Products: https://www.fao.org/dairy-production-products/en/ - FAO Animal Production and Health: https://www.fao.org/animal-production/en/ - WOAH (World Organisation for Animal Health): https://www.woah.org/en/home/ > This article is educational and is not a substitute for veterinary diagnosis, treatment, public-health guidance, or regulatory reporting.