Feed Testing for Livestock: How to Use Lab Results in Ration Balancing

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-08-14

Key Takeaways

• Strategic Sampling is Paramount: Accurate feed testing hinges on correct sampling; for baled forages, use a probe on 10-20 bales per lot, and for silage, sample from multiple locations on the face after fermentation, discarding spoiled outer layers.
• Ruminant Nutritional Pillars: For ruminants, prioritize Dry Matter (DM), Crude Protein (CP), Neutral Detergent Fiber (NDF), Acid Detergent Fiber (ADF), and Relative Feed Value (RFV)/Relative Forage Quality (RFQ) to assess energy, intake potential, and digestibility.
• Mineral Imbalances Pose Significant Risks: Critical minerals like Calcium, Phosphorus, Magnesium, and Potassium directly impact metabolic health, with ratios (e.g., Ca:P) and levels influencing conditions like milk fever and grass tetany.
• Nutrient Requirements Dictate Ration Formulation: Compare laboratory feed analysis results against established livestock nutrient requirements (e.g., NRC tables) for specific animal classes and production stages to identify deficiencies or excesses.
• Dynamic Monitoring and Retesting are Essential: Feed composition changes post-harvest and during storage; retest forages after several months and monitor animal performance (body condition, production) to adjust rations accordingly.
• Actionable Thresholds for Critical Nutrients: Be aware of decision thresholds for nutrients like nitrates (below 0.5% DM safe, above 1.0% DM dangerous) and protein (below 7% CP inadequate for rumen function) to prevent toxicity and optimize animal health.

Every livestock operation depends on feed as its largest recurring cost, yet many farmers still balance rations using book values or last year's hay test. Those shortcuts cost money in wasted supplement, lost gain, or reduced milk production. Feed testing removes the guesswork. A laboratory analysis tells you exactly what is in your forage, grain, or mixed ration, and that information lets you build a ration that meets your animals' needs without overspending on ingredients they do not require.

This guide is for beef and dairy cattle producers, sheep and goat keepers, and anyone who buys or grows forage for livestock. It walks through the entire process: when to test, how to sample correctly, what each lab result means, how to use those numbers in ration balancing, and how to track changes across seasons and storage periods. You will also find practical guidance on avoiding common sampling errors, interpreting confusing results, and knowing when to call your veterinarian or extension agent for help.

At a Glance

• Test every new cutting or lot of hay, haylage, silage, or grain before you feed it. A single test per lot is the minimum, and two or more samples per lot improve confidence.
• Sample correctly or the lab results are meaningless. Use a hay probe for baled forage, collect cores from at least 10 to 20 bales per lot, and sample silage from the face after fermentation is complete.
• The most important numbers for ruminants are dry matter, crude protein, neutral detergent fiber (NDF), acid detergent fiber (ADF), and relative feed value (RFV) or relative forage quality (RFQ) for legumes and grasses.
• Minerals matter more than many farmers realize. Calcium, phosphorus, magnesium, potassium, and sulfur levels affect everything from milk fever risk to grass tetany.
• A feed test is only useful if you compare it to your animals' requirements. Use extension tables or a nutritionist's software to match the test results to the correct class of livestock.
• Retest after storage changes. Hay that sat in the barn for eight months is not the same feed it was at baling time.
• Keep records of every test and every ration. Year over year records help you spot trends in your soil, your harvest timing, and your storage management.
• Call your veterinarian or extension agent when test results suggest a toxicity risk, when animals are not performing as expected despite a balanced ration, or when you suspect a sampling error.

Why Feed Testing Matters More Than You Think

The single biggest mistake in livestock nutrition is assuming that all hay is alike. A field of mixed grass hay cut in early June is a completely different feed than the same field cut in August. The protein content can drop by half, the fiber content can climb, and the energy available to the animal changes dramatically. Without a test, you are feeding blind.

Forage testing for cattle and hay analysis for sheep are not optional extras on well run farms. They are the foundation of every cost effective ration. Consider what happens when you skip the test. You might assume your grass hay is 12 percent crude protein because that is what a neighbor's test showed last year. If your hay is actually 8 percent protein, your lactating ewes or growing steers will lose condition no matter how much they eat. If your hay is actually 16 percent protein, you are wasting money on protein supplement they do not need.

The same logic applies to energy. Hay cut late is lower in digestible energy than hay cut early. Animals eat less of it because it is more fibrous, and they extract less energy from each pound. You can feed the same weight of hay and still see poor gains or falling milk production. The feed test tells you the energy value so you can adjust the amount you feed or add a supplement to close the gap.

Feed testing also protects your animals from hidden dangers. High nitrate levels in drought stressed forages, high sulfur from certain water sources or feed ingredients, and mineral imbalances that cause grass tetany are all detectable with the right tests. A standard forage analysis will catch many of these issues before they become veterinary emergencies.

Understanding the Laboratory Report

When you open a feed test report, you will see a table of numbers. Each one describes a different aspect of the feed's composition. You do not need to memorize every value, but you do need to understand the ones that drive your ration decisions.

Dry Matter and Moisture

Dry matter (DM) is the percentage of the feed that is not water. It is the foundation for every other calculation. If your hay is 90 percent dry matter and 10 percent moisture, then 100 pounds of that hay contains 90 pounds of actual feed material. All nutrient values on a lab report are expressed either "as fed" (including moisture) or "on a dry matter basis" (excluding moisture). Always balance rations on a dry matter basis for consistency.

Moisture content matters for storage and intake. Hay above 15 percent moisture can heat and mold in the bale. Silage and haylage should be in the 30 to 60 percent moisture range depending on the structure used. If the moisture is too high, fermentation is poor and spoilage increases. If it is too low, the feed may heat and lose digestible protein.

Crude Protein

Crude protein (CP) is an estimate of the total protein in the feed. It is calculated by measuring nitrogen and multiplying by 6.25, because protein is about 16 percent nitrogen. This method measures all nitrogen, including non protein nitrogen like urea, so it can overestimate true protein in some feeds. For most farm forages, crude protein is a reliable starting point.

Protein requirements vary by animal class. A dry beef cow needs only 7 to 9 percent crude protein in her diet. A lactating dairy cow needs 16 to 18 percent. A growing lamb or calf needs 14 to 16 percent. Your feed test tells you where your forage stands, and the gap between forage protein and animal requirement tells you how much supplement you need.

Some labs also report soluble protein, degradable protein, and undegradable protein. These fractions matter for high producing dairy cows and growing ruminants. If you are feeding a simple beef cow herd or a small sheep flock, the total crude protein number is usually sufficient.

Fiber Fractions

Fiber is the structural part of the plant that gives it rigidity. Ruminants can digest some fiber through the action of rumen microbes, but fiber is less digestible than the cell contents. The two main fiber measurements are neutral detergent fiber (NDF) and acid detergent fiber (ADF).

ADF is the least digestible portion of the plant, including cellulose and lignin. It correlates with digestibility. Lower ADF means higher digestibility and more energy. Alfalfa hay with an ADF of 30 percent is higher quality than the same hay with an ADF of 40 percent.

NDF includes ADF plus hemicellulose. It correlates with intake potential. Higher NDF means the feed is bulkier and the animal can eat less of it before feeling full. NDF also matters for rumen health. Cows need enough effective fiber to maintain proper rumen function and milk fat percentage.

The ratio of NDF to ADF tells you something about the plant species and maturity. Legumes like alfalfa have lower NDF than grasses at the same maturity. Grasses tend to have higher NDF but the fiber is often more digestible than legume fiber.

Relative Feed Value and Relative Forage Quality

Relative feed value (RFV) is a single number that combines digestibility and intake potential. It is calculated from ADF and NDF and is used mostly for alfalfa and other legumes. RFV of 100 equals full bloom alfalfa. Higher numbers mean better quality. RFV above 150 is excellent, 125 to 150 is good, 100 to 125 is fair, and below 100 is poor.

Relative forage quality (RFQ) is a newer index that accounts for fiber digestibility. It is more accurate for grasses and for mixtures. RFQ uses the same scale as RFV, so a 130 RFQ grass hay is comparable to a 130 RFV alfalfa. If your lab reports both, use RFQ for grasses and RFV for legumes, or use RFQ for everything since it is the more precise measure.

These indices are useful for marketing hay and for comparing lots. They are less useful for ration balancing because they do not tell you the actual nutrient values. Always balance on the component values, not the index.

Energy Values

Labs report energy in several ways. Total digestible nutrients (TDN) is the classic measure. Net energy for maintenance (NEm), net energy for gain (NEg), and net energy for lactation (NEl) are more precise for specific production stages. These values are calculated from the fiber and protein fractions using equations developed by nutrition researchers.

For beef cattle, NEm and NEg are the numbers you use. For dairy cattle, NEl is the standard. For sheep and goats, TDN or NEm works well. The lab report will list all of these values, and your ration balancing method will determine which one you need.

Minerals

The standard forage test includes calcium, phosphorus, magnesium, potassium, and often sulfur. These minerals play critical roles in bone development, muscle function, enzyme systems, and reproduction. Imbalances cause real problems.

Calcium to phosphorus ratio matters. Ruminants need a ratio of about 2 to 1, and the diet should never be below 1 to 1. Legumes are high in calcium and low in phosphorus. Grains are the opposite. Grass hay is intermediate. If you feed only legume hay, you need phosphorus supplementation. If you feed only grain, you need calcium.

Potassium levels are important for dry cow management. High potassium forages increase the risk of milk fever in dairy cows at calving. The dietary cation anion difference (DCAD) approach to dry cow nutrition depends on knowing the potassium and sulfur content of your forages.

Magnesium is critical for preventing grass tetany. Forages grown on soils low in magnesium or high in potassium and nitrogen can be dangerously low in magnesium. A forage test that shows low magnesium tells you to supplement.

Nitrates

Nitrate testing is essential for forages grown under drought stress, after heavy nitrogen fertilization, or from fields with high manure application. Nitrates accumulate in the lower part of the plant stem when growth is stunted. When ruminants consume high nitrate forage, the nitrate converts to nitrite in the rumen and interferes with oxygen transport in the blood.

Safe levels are below 0.5 percent nitrate on a dry matter basis. Levels from 0.5 to 1.0 percent are risky and should be limited in the diet. Levels above 1.0 percent are dangerous and should not be fed free choice. If your lab report shows elevated nitrates, dilute the forage with low nitrate feeds and test the final ration.

Mycotoxins

Some labs offer mycotoxin panels for grains, silage, and hay. Mycotoxins are produced by molds and can cause reduced intake, poor gains, reproductive problems, and immune suppression. Testing for mycotoxins is more expensive than a standard forage test, so it is usually reserved for suspect feeds. If you see visible mold, if animals are off feed, or if you are feeding grain that was stored poorly, ask your lab about a mycotoxin screen.

How to Sample Forages Correctly

The lab can only analyze what you send. A poor sample produces misleading results, and misleading results lead to bad feeding decisions. Sampling is the most important step in the entire process, and it is the step most often done wrong.

Sampling Hay Bales

You need a hay probe. A hay probe is a hollow metal tube that you drill into the end of a bale to remove a core sample. Do not pull handfuls from the outside of bales. The outside is weathered and does not represent the whole bale. Do not sample from fallen leaves or broken flakes. Those are not representative either.

For small square bales, sample from the center of the end of the bale, pushing the probe all the way through. For large round bales, sample from the side, aiming toward the center. For large square bales, sample from the end or the side, avoiding the outer 6 inches.

Collect cores from at least 10 bales per lot. If the lot is large or variable, collect 15 to 20 cores. A lot is a group of bales from the same field, cut at the same time, and stored the same way. If you cut a field in June and again in August, those are two lots. If half the field is alfalfa and half is grass, those are two lots.

Combine all cores into one clean plastic bag. Mix them thoroughly. Send at least one full quart of material to the lab. If you are sampling multiple lots, use separate bags and label each one clearly.

The best time to sample hay is about three to four weeks after baling, once the hay has gone through its initial heating phase. Sampling earlier can give misleading moisture and protein readings. If you are buying hay, sample before you buy or immediately after delivery so you can adjust the ration right away.

Sampling Haylage and Silage

Silage sampling is trickier because the feed is wet and variable. The fermentation process changes the nutrient profile over time. Sample from the face of the silo or bunker after the silage has fermented for at least three to four weeks.

Take samples from multiple locations across the face, from top to bottom and side to side. Discard the outer 6 inches of spoiled material first. Collect a handful from each location and combine them in a clean bucket. Mix well and fill a plastic bag with about one quart of material.

For baled silage or haylage, sample with a probe just like dry hay, but be prepared for a wetter, stickier sample. Collect cores from at least 10 bales per lot and combine them.

If you are sampling from an upright silo, sample after unloading a few inches from the surface. If you are sampling from a pile or drive over pile, sample from several locations on the face.

Silage samples are perishable. Pack the bag tightly to exclude air, seal it, and ship it to the lab the same day. If you cannot ship immediately, refrigerate the sample. Do not freeze it because freezing changes some nutrient values.

Sampling Grains and Concentrates

Grain sampling is simpler but still requires care. Sample from multiple bags, bins, or parts of a bulk load. Use a grain probe if you have one. Combine the samples in a clean bucket, mix well, and fill a quart bag.

For wet grains like high moisture corn, sample from the storage structure after fermentation is complete. For dry grains, sample from the bin after the grain has been turned or mixed. If you are buying a new load of grain, sample from the truck or wagon at delivery.

Labeling and Shipping

Every sample needs a label with your name, the date, the feed type, and a lot identifier. Use a permanent marker on the bag itself and include a paper label inside the bag. The lab needs to know what the feed is so they can choose the right analysis package.

Complete the lab submission form carefully. Indicate whether the sample is hay, haylage, silage, grain, or a total mixed ration. Indicate the plant species if you know it. Indicate whether you want a basic analysis or a full analysis with minerals and nitrates.

Ship samples early in the week so they do not sit in a warehouse over the weekend. Use a rigid container to prevent crushing. Most labs have sample bags and submission forms available on request.

Choosing the Right Analysis Package

Labs offer several levels of testing. The basic package for forages typically includes dry matter, crude protein, ADF, NDF, and calculated energy values. This is enough for many beef cow operations and for sheep and goat producers who are feeding average quality forage.

The next level adds minerals. This package includes calcium, phosphorus, magnesium, potassium, and often sulfur. It costs more but is worth it for dairy operations, for dry cow programs, and for any producer who has seen mineral related problems.

The full package adds nitrate testing and sometimes a more detailed protein fractionation. This is the package to choose for drought stressed forages, for corn silage, and for any feed that looks questionable.

Grain testing is different from forage testing. Grains need analysis for dry matter, crude protein, and sometimes starch and fiber. If you are buying byproducts like distillers grains, soybean hulls, or wheat middlings, test each load because these products vary widely.

Your local extension office can recommend a lab and help you interpret the results. Many land grant universities operate forage testing labs with reasonable fees. Private labs are also available and often offer faster turnaround. Choose a lab that uses near infrared reflectance spectroscopy (NIRS) or wet chemistry methods. Both are reliable when done by experienced labs.

How to Use Feed Test Results in Ration Balancing

You have the lab report in hand. Now you need to turn those numbers into a ration. The process has four steps: identify your animals' requirements, compare the feed test to those requirements, calculate how much of each feed to offer, and adjust based on observed animal performance.

Step 1: Know Your Animals' Requirements

Every class of livestock has published nutrient requirements. The National Research Council (NRC) tables are the standard reference, and your extension office or nutritionist can provide the relevant numbers. The requirements depend on body weight, stage of production, and expected performance.

A dry, mature beef cow in mid gestation needs about 8 percent crude protein and 50 percent TDN in her diet. The same cow in early lactation needs 11 percent protein and 60 percent TDN. A growing steer gaining 3 pounds per day needs 13 percent protein and 75 percent TDN. A lactating dairy cow producing 80 pounds of milk per day needs 17 percent protein and 75 percent TDN.

Sheep and goats have their own requirement tables. A mature ewe in early gestation needs about 10 percent protein. The same ewe nursing twins needs 14 to 15 percent protein. Growing lambs need 14 to 16 percent protein depending on growth rate.

Write down the requirements for your specific animals before you open the feed test. This prevents you from making ration decisions without a target.

Step 2: Compare Feed Test to Requirements

Look at the crude protein and energy values from your feed test. Compare them to your animals' requirements. This comparison tells you whether your forage is adequate alone or whether you need supplement.

Example: Your grass hay tests at 8 percent crude protein and 55 percent TDN. Your lactating beef cows need 11 percent protein and 60 percent TDN. The hay is short on both protein and energy. You need to supplement with a higher protein feed and possibly increase energy density.

Example: Your alfalfa hay tests at 18 percent crude protein and 58 percent TDN. Your dry beef cows need 8 percent protein and 50 percent TDN. The hay exceeds both requirements. You can feed the hay alone, but you are paying for more protein than the cows need. If the hay is expensive, you might blend it with lower quality grass hay to reduce cost.

The mineral comparison works the same way. Your feed test shows calcium at 0.5 percent and phosphorus at 0.2 percent. Your lactating cows need 0.4 percent calcium and 0.25 percent phosphorus. The calcium is adequate but the phosphorus is slightly low. Add a phosphorus supplement or choose a mineral mix with higher phosphorus.

Step 3: Calculate the Ration

Ration balancing can be done by hand with simple math, with extension worksheets, or with computer software. The basic approach is to combine feeds so the total diet meets or slightly exceeds the requirements.

Start with the forage. Decide how much forage the animals will eat. A good starting point is 2 percent of body weight on a dry matter basis for mature ruminants. A 1,200 pound cow eats about 24 pounds of dry matter per day. A 150 pound ewe eats about 3 pounds of dry matter per day.

If the forage meets all requirements, you are done. If not, you need to add supplements.

For protein, calculate the gap between the forage protein and the requirement. Then choose a supplement with known protein content. Soybean meal is about 50 percent protein. Cottonseed meal is about 45 percent protein. Corn gluten feed is about 20 percent protein. Divide the protein gap by the supplement protein percentage to find how much supplement to feed.

Example: Your cows need 11 percent protein and the hay provides 8 percent. The gap is 3 percentage points. On a 24 pound dry matter intake, that is 0.72 pounds of protein. Soybean meal at 50 percent protein provides 0.5 pounds of protein per pound of feed. You need about 1.4 pounds of soybean meal per cow per day.

For energy, the calculation is similar but uses TDN or net energy values. If the forage is short on energy, you can add grain, byproduct feeds, or increase the amount of higher energy forage in the diet. Corn is about 88 percent TDN. Add enough to close the energy gap without exceeding safe starch levels.

Minerals are usually corrected with a commercial mineral supplement. Choose a mineral mix that fills the specific gaps in your forage test. If your forage is high in calcium and low in phosphorus, choose a mineral with no added calcium and higher phosphorus. If your forage is low in magnesium, choose a high magnesium mineral.

Step 4: Monitor and Adjust

A ration is a starting point, not a final answer. Animals vary in their intake, the actual feed varies from the test, and conditions change. Watch your animals closely for the first two to three weeks on a new ration.

Check body condition. Cows and ewes should maintain or improve condition depending on their stage of production. Weigh animals if you can, or use body condition scoring. If animals are losing condition, increase the energy or protein in the diet. If they are gaining too much, reduce the supplement.

Check manure. Manure consistency reflects rumen function. Loose, watery manure can mean too much starch or too much protein. Very dry, hard manure can mean too little protein or too much fiber. Adjust the ration gradually and watch for changes.

Check milk production and milk fat. Dairy producers should see stable or increasing milk production on a balanced ration. A drop in milk fat percentage can mean too little effective fiber. A drop in milk protein can mean too little energy.

Check intake. Animals should clean up their feed without leaving excessive refusals. If they are leaving feed, the ration may be too bulky, too high in certain minerals, or unpalatable. If they are cleaning the bunk completely and still looking hungry, increase the amount offered.

Common Mistakes in Feed Testing and Ration Balancing

Even experienced producers make errors in this process. The most common mistakes are sampling errors, ignoring mineral levels, using outdated requirements, and failing to retest after storage changes.

Sampling Errors

The most common sampling error is taking too few cores. One or two bales do not represent a whole lot. Hay varies from bale to bale based on soil fertility, plant density, and moisture at baling. Ten cores minimum is the rule, and more is better.

Another common error is sampling only the good bales or only the bad bales. If you sample the best bales, you will overestimate feed quality and underfeed your animals. If you sample the worst bales, you will underestimate quality and waste money on unnecessary supplement. Sample randomly across the lot.

Sampling at the wrong time is another mistake. Hay sampled immediately after baling is still going through respiration and heating. The moisture content changes, and protein values can shift. Wait three to four weeks after baling.

Ignoring Minerals

Many producers test for protein and fiber but skip the mineral analysis to save money. This is a false economy. Mineral imbalances cause real production losses and health problems that cost far more than the price of a mineral test.

Grass tetany is a classic example. It strikes lactating cows and ewes grazing lush, fast growing grass that is low in magnesium and high in potassium. The animals go down, convulse, and can die within hours. A forage test that shows low magnesium and high potassium tells you to supplement magnesium before the problem appears.

Milk fever is another example. It is caused by a calcium metabolism failure at calving, and the risk is influenced by the potassium content of the dry cow diet. High potassium forages increase the risk. A forage test on dry cow hay tells you whether you need to use anionic salts or other DCAD strategies.

Using Outdated Requirements

Animal nutrient requirements have been refined over decades of research. The NRC updates its publications periodically, and extension services publish current recommendations. Using a requirement table from 20 years ago can lead to significant errors, especially for high producing animals.

The same applies to feed composition tables. Book values for average hay or average corn are useful for planning but not for final ration balancing. Your feed is not average. It is specific to your field, your harvest date, and your storage. Test it.

Failing to Retest

Feed changes over time. Hay loses dry matter and can lose vitamin content during storage. Silage continues to ferment and can change in nutrient value for months. High moisture grains go through similar changes.

If you feed from a silo for six months, the silage you feed in March is not identical to the silage you tested in October. The fermentation continues, and the nutrient profile shifts. Retest at least once mid storage, and more often if you see animal performance changes.

The same applies to hay. Hay stored in a humid barn can pick up moisture and mold. Hay stored in a dry shed stays more stable. If you notice musty smells, visible mold, or changes in animal intake, retest before you continue feeding.

Overlooking Nitrates

Nitrate testing is easy to skip, especially when the forage looks good. But drought stressed corn, sudan grass, and even some weeds can accumulate dangerous nitrate levels. The risk is highest after a drought followed by rain, because the plant takes up nitrogen but does not grow enough to dilute it.

If you are feeding any forage that was stressed during the growing season, test for nitrates. The test is inexpensive compared to the cost of losing animals to nitrate poisoning.

Balancing for the Average Animal

Rations are usually balanced for the average animal in the group, but animals within a group vary. A group of cows includes some that are older, some that are younger, some that are heavier, and some that are thinner. The average requirement may not meet the needs of the extremes.

For most operations, balancing for the average is acceptable if you monitor body condition and adjust for thin or fat animals. For high producing dairy herds, group animals by production level and balance a separate ration for each group.

Decision Thresholds and Action Levels

Some feed test results require immediate action. Knowing the thresholds helps you respond quickly and correctly.

Protein Levels

For beef cows, forage with less than 7 percent crude protein will not support adequate rumen function. The microbes that digest fiber need nitrogen. Below 7 percent, intake drops and digestibility suffers. Supplement protein is essential.

For lactating beef cows, forage below 10 percent protein requires supplementation. For growing calves, below 12 percent is inadequate. For lactating dairy cows, forage below 15 percent requires substantial protein supplementation.

For sheep, forage below 8 percent protein is inadequate for most production stages. Lactating ewes need 12 to 14 percent. Growing lambs need 14 to 16 percent.

Energy Levels

Forage with TDN below 50 percent is low energy feed. Dry cows can maintain condition on it if they are not lactating, but lactating animals will lose weight. TDN below 45 percent is poor quality feed that needs significant energy supplementation.

For dairy cows, forage with NEl below 0.55 Mcal per pound is low energy. High producing cows need forage with NEl above 0.65 Mcal per pound, plus grain to reach their energy requirements.

Fiber Levels

For dairy cows, NDF in the total ration should be 25 to 33 percent. Forage NDF should be at least 19 percent of the total diet dry matter. Below that, milk fat depression becomes a risk.

For beef cattle, NDF above 60 percent in forage limits intake significantly. Forage with NDF above 65 percent is very low quality and may not support even dry cows without supplementation.

Nitrate Levels

Nitrate levels are reported as nitrate ion (NO3) or as nitrate nitrogen (NO3-N). The thresholds differ. If your lab reports nitrate ion, levels below 0.5 percent are safe. Levels of 0.5 to 1.0 percent are risky. Levels above 1.0 percent are dangerous.

If your lab reports nitrate nitrogen, levels below 0.1 percent are safe. Levels of 0.1 to 0.2 percent are risky. Levels above 0.2 percent are dangerous.

If your test shows risky or dangerous nitrate levels, do not feed the forage free choice. Dilute it with low nitrate feeds. Limit the high nitrate feed to less than 25 percent of the diet dry matter for risky levels. For dangerous levels, do not feed it at all without veterinary guidance.

Mineral Imbalances

Calcium to phosphorus ratio above 4 to 1 can interfere with phosphorus absorption and cause urinary calculi in male animals. If your forage test shows a very wide calcium to phosphorus ratio, add phosphorus or choose a mineral supplement with phosphorus.

Potassium above 3 percent in dry cow forages increases milk fever risk. If your dry cow hay tests above 3 percent potassium, work with your veterinarian or nutritionist on a DCAD program.

Magnesium below 0.2 percent in lush spring grass increases grass tetany risk. If your forage test shows low magnesium, start magnesium supplementation before turning animals out.

Sulfur above 0.4 percent in the total diet can interfere with copper absorption and cause polioencephalomalacia in ruminants. If your forage or water tests high in sulfur, investigate the source and adjust the diet.

Monitoring and Recordkeeping

Feed testing is not a one time event. It is a management system. The value comes from tracking results over time and using that history to make better decisions.

What to Record

For every feed test, record the date, the field or source, the harvest date, the storage method, and the lot identifier. Record all the nutrient values from the lab report. Record the ration you fed based on that test. Record animal performance during the period you fed that ration.

Keep these records in a notebook, a spreadsheet, or a farm management app. The format matters less than the consistency. You want to be able to look back at five years of hay tests and see how your forage quality has changed.

What to Watch For

Year over year trends in forage quality tell you about your soil fertility, your harvest timing, and your weather. If your hay protein has been declining for three years, your soil may be short on nitrogen or your harvest may be getting later. If your forage fiber is climbing, you may be cutting too late or your alfalfa stand may be thinning.

Trends in animal performance tell you whether your ration balancing is working. Track average daily gain, milk production, body condition scores, and breeding rates. If performance declines even though your feed tests look good, the problem may be elsewhere: parasites, disease, or management stress.

When to Retest

Retest when you open a new storage structure or start feeding a new lot. Retest when you notice changes in feed appearance, smell, or animal intake. Retest after any major weather event that could have affected stored feed, such as a roof leak or a flood.

If you buy feed from a new supplier, test the first load and compare it to what you ordered. If you buy the same product from the same supplier regularly, test periodically to confirm consistency.

When to Call a Veterinarian or Extension Agent

Most feed testing questions can be answered by your extension agent or a qualified nutritionist. But some situations require veterinary involvement.

Call your veterinarian immediately if you suspect nitrate poisoning. Clinical signs include rapid breathing, weakness, tremors, blue mucous membranes, and sudden death. This is an emergency. Do not wait for test results if animals are showing signs. Remove the suspect feed and call your vet.

Call your veterinarian if animals are not performing as expected despite a balanced ration. Weight loss, poor milk production, reproductive problems, or unexplained illness can have nutritional causes, but they can also be caused by disease. Your vet can help you rule out health problems and adjust the nutrition program.

Call your veterinarian if you see signs of mineral toxicity or deficiency. Grass tetany, milk fever, white muscle disease, and urinary calculi are all manageable conditions, but they need prompt treatment. Your vet can treat affected animals and help you adjust the ration to prevent more cases.

Call your extension agent for help with sampling technique, lab selection, ration balancing, and interpretation of results. Extension agents have access to current requirement tables, local feed composition data, and often free or low cost software for ration balancing. They can also help you understand the economic tradeoffs between different feeding strategies.

Call your extension agent if you are considering a major change in your feeding program, such as switching from dry hay to silage, adding byproduct feeds, or implementing a rotational grazing system. They can help you plan the transition and avoid costly mistakes.

Frequently Asked Questions

How often should I test my hay or silage?

Test every new lot before you feed it. A lot is any group of feed from the same field, cut at the same time, and stored the same way. If you cut a field once a year, that is one test per year for that field. If you cut three times, that is three tests. Retest stored feeds after several months because nutrient values change during storage. For silage, test at feedout and retest midway through the storage period.

What is the difference between RFV and RFQ, and which should I use?

Relative feed value (RFV) is calculated from ADF and NDF and predicts digestible dry matter intake. Relative forage quality (RFQ) also accounts for fiber digestibility, so it is more accurate for grasses and grass legume mixtures. Use RFQ when it is available. Use RFV for pure legume hay if that is what your lab reports. Both use the same scale, so a 130 RFQ is comparable to a 130 RFV. For ration balancing, use the component values like protein, TDN, and minerals rather than the index numbers.

Can I test hay that is already being fed, or is it too late?

You can test hay at any time, including hay that is already in the feeder. The results will help you adjust the ration going forward, which is still valuable. But you lose the ability to make good buying decisions if you already purchased the hay. Test new purchases before you buy or immediately after delivery so you know what you are feeding.

How much does a feed test cost, and is it worth it?

A basic forage test costs roughly 15 to 30 dollars. A full test with minerals and nitrates costs roughly 40 to 60 dollars. Compare that to the cost of feed. A single bale of hay can cost more than the test. If the test helps you avoid one mistake in supplement purchasing or prevents one case of nitrate poisoning, it pays for itself many times over. For most operations, testing every lot is the most cost effective management decision you can make.

My hay test shows low protein. Can I just feed more hay to make up the difference?

No. If hay is low in protein, feeding more of it does not solve the problem. The hay is low in protein because the plant was mature or the soil was deficient. Feeding more hay gives the animal more total protein, but it also gives more fiber and reduces energy density. The animal may not be able to eat enough to meet her protein needs. You need to supplement with a higher protein feed or replace some of the low quality hay with better forage.

What does it mean if my silage test shows high ammonia nitrogen?

High ammonia nitrogen in silage indicates extensive protein breakdown during fermentation. This happens when the crop was too wet, the silo was packed poorly, or fermentation was slow. High ammonia nitrogen means the protein is less available to the animal. It can also reduce feed intake because of the strong smell. If ammonia nitrogen is above 10 to 15 percent of total nitrogen, the silage quality is poor. Work with your nutritionist to adjust the ration and consider improving your harvest and packing practices next season.

Should I test my water too?

Yes, especially if animals are drinking from wells, ponds, or streams. Water can contain high levels of sulfates, nitrates, and total dissolved solids that affect animal health and performance. High sulfate water can cause polioencephalomalacia and interfere with copper absorption. High nitrate water adds to the nitrate load from feed. Test your water at least once a year, and more often if you suspect a problem.

How do I know if my feed test results are accurate?

Choose an accredited lab with experience in forage analysis. Most labs participate in proficiency testing programs that verify their accuracy. If you get a result that seems wildly off, consider resampling and retesting before making major changes. Sampling error is more common than lab error, so if you only took a few cores, take more cores and test again.

Related Farming Guides

This space will be populated with links to related farming guides on feed management, livestock nutrition, forage production, and herd health. Check back for updated resources on ration balancing, grazing management, and seasonal feeding strategies.

Related Clinical & Scientific Guides

• Animal Welfare Audits: Building a Useful Farm Program
• Total Mixed Ration (TMR) for Dairy: Mixing and Feeding Management
• Feed Additives for Livestock: Probiotics, Enzymes, and More

References

• USDA Farm Management: https://www.farmers.gov/
• FAO Farm Management: https://www.fao.org/farmer-field-schools/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.