Forage quality changes with maturity and storage. A forage test can provide useful information about the nutritive value of hay or pasture. This information can be used to adjust the amount of supplement fed to beef cattle. If forage quality is high, the producer can feed less supplement, resulting in savings. Conversely, if the forage quality is low, diet supplementation can improve animal performance and increase profits. This fact sheet reviews how to take a forage sample and how to interpret laboratory results.
Taking a Forage Sample
Forage test forms can be obtained from your county Extension office. These forms contain complete instructions on how to collect forage samples. Proper collection and identification of a sample are very important. A tool is needed to collect hay samples. Your local Extension office may have a forage sampling probe. This device consists of a long tube with a cutting edge on one end and a shank on the other that can be fastened to an electric drill or hand brace. Laboratories may have specific instructions that should be followed.
Basic forage sampling procedures:
- To correctly sample a rectangular bale, the bit is driven into the end of 15–20 bales from a particular lot of hay. Drill to the full depth of the sample tube on loose bales and half its depth in tight bales. Mix the cores thoroughly and send the entire sample to the lab in a sealed plastic bag.
- Large round bales should be sampled on the rounded side of the bale. Collect a single sample from each of 10–12 bales from the same lot, combining the core samples into one sample for analysis. If the outer layer of the round bale is weathered, pull away 1–2 inches of the bale’s outer layer and then collect the sample. Drill to the full depth of the tube.
- Place samples in a clean plastic bucket and thoroughly mix them. Pour the entire mixed sample onto a clean flat surface. Level the sample and separate it into equal quarters. Select the two opposing quarters (being sure to include the hay fines). If the sample is too large, repeat the quartering process until the desired size is reached.
Each hay type and cutting should be sampled and analyzed separately. Hay harvested on different dates within a cutting should also be sampled separately. Therefore, it is important that each cutting is stored and marked separately in order to allow it to be identified with its forage test. When sampling forages, one cannot overstress the importance of using a proper sampling technique. Samples should be representative and selected at random. In summary, sample each lot of forage separately and make sure the forage can be identified with its analysis when feeding it to beef cattle.
Silage can also be analyzed. To sample silage, run the unloader and collect from the feed bunk in five to six places. Put four handfuls of silage into plastic or vacuum-sealed bags. Collect samples for two or three days and then mix them thoroughly and subsample 1–2 pounds. Refrigerate samples in a plastic bag during the collection period. Seal the bag, attach a completed tag, and mail it immediately or freeze the sample and mail it to the laboratory.
Bagged silage can be sampled by cutting slits along the side of the bag in five to six places. Collect handfuls through the slits and mix them in a clean plastic bucket. Mix well and bag them in plastic with a tag. Reseal slits with silage bag tape.
Silage can also be sampled while it is going into the silo. Collect representative samples from each wagon as silage is unloaded and mail them immediately or freeze the samples. Take the same number of samples from each wagon and keep them in a container. If the silage lot changes because samples are being taken from a particular hybrid, field, or another area of the farm, start another container. When all samples have been collected, mix the sample within each container and collect a random 1–2-pound subsample for analysis. Seal it in a plastic bag and send it to the lab immediately or freeze it if it can't be mailed promptly. Fresh silage samples are a good way to plan your feeding program. However, it is a good idea to sample silages when they are being fed and have gone through the fermentation process.
Pastures can be sampled by collecting pasture grass at the height animals are grazing. Collect random grab samples of forage from several locations. Air-dry the sample, if possible, before sending it to the laboratory. This can be done by hanging the forage inside a burlap bag for about a week. Fresh samples should be mailed immediately.
There are many reasons to forage test. If you are considering testing your forage, most forage testing labs can provide forage or feed analysis. Be sure to mail samples early in the week, especially silage samples.
Interpreting Lab Test Results
Let's say you have sampled four lots of different hay. Let's look at some typical lab results from an analytical laboratory. Table 1 lists samples taken from hay produced on a farm in Guernsey County. These samples were harvested in mid- to late June.
Now that we have our results, how do we use them and what do they mean? As a hay producer, you probably have a similar scenario—several lots of hay, each with a different nutrient composition. Let's go through our report and look at the differences between each nutrient and determine how we might use these forages. As we consider the nutrient levels in our hay, we should consider the animal's sex, weight, daily gain, stage of production, and environmental conditions.
Below are forage test results from one farm of various cuts of forage as hay and different fields.
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Dry Matter (DM)
Beef cows will consume approximately 2%–2.5% of their body weight in dry matter (DM) per day of good quality forage. This means that a 1,000-pound cow would consume 25 pounds (1,000 x 0.025) of DM per day. This is approximately 30 pounds of hay (sample 158 Alfalfa/Orchard Grass from Table 1), which is calculated as 25 / 0.833 = 30. This triggers the questions: "Is it possible for the cows to eat this much hay?” and "Am I supplying enough feed to meet their DM needs?" For cattle, the ability to consume enough forage is affected by the fiber content. For this reason, as their neutral detergent fiber intake increases, their forage intake decreases. In addition, proper dry matter content of hay and silage is essential for successful storage.
Crude Protein (CP)
Protein percentages for these hay types come in a range. Recommended crude protein levels, as a percentage of dry matter (DM), range from approximately 7.5% for mid-gestation mature dry cows to approximately 13% for cows nursing calves in peak milk. Sample 158 of the Alfalfa/Orchard Grass on Table 1 supplies enough nutrients to support a dry cow and would meet most of the nutrient requirements of a lactating cow. Therefore, the best use of this hay is on growing replacement heifers and pregnant and lactating cows.
A supplement is needed to meet the protein needs of cows being fed the other analyzed hay sources from Table 1. A popular nonprotein nitrogen source is urea. Urea must be fed with care since it rapidly decomposes to ammonia in the rumen. Large quantities of urea can cause ammonia toxicity that is potentially fatal. When feeding urea to beef cattle, be sure to mix rations well. Furthermore, calves under 450 pounds will gain more efficiently on natural protein rather than a nonprotein nitrogen source. One common grain supplement used in mixed rations to supply protein is soybean meal.
| Grass Hay | Crude Protein (CP) Content |
| Premium quality | 13%+ |
| Good quality | 9%–13% |
| Fair quality | 5%–9% |
| Alfalfa Hay not more than 10% Grass | |
| Premium quality | 20%–22% |
| Good quality | 18%–20% |
| Fair quality | 16%–18% |
Acid Detergent Fiber (ADF)
Acid detergent fiber (ADF) is a measure of cellulose and lignin. In general, as plants mature, indigestible fiber content increases along with ADF. As the amount of ADF in the forage increases, digestibility decreases. Neutral detergent fiber also increases as plants become more reproductively mature. To increase the ability of beef cattle to digest poor-quality forage, chop the hay into shorter fiber lengths. The shorter length allows cattle to eat more while improving their forage digestibility significantly (Fluharty, 2016).
Typical forage ADF values for orchard grass, smooth bromegrass, and timothy as a percentage of dry matter:
- Grass ADF levels range from less than 32%–35% vegetative to 35%–40% for early-late bloom.
- Alfalfa/grass mixture ADF levels range from less than 36% to 40%.
(Cole, n.d.)
As our Table 1 samples illustrate, all our hay sources have high ADF values. Total dry matter intake decreases as ADF levels increase. These hay sources would have been relatively mature at the time of harvest.
Neutral Detergent Fiber (NDF)
Neutral detergent fiber (NDF) is the amount of cellulose, lignin, and hemicellulose in the forage. This material makes up the majority of the cell wall of plants. As the NDF values increase, plant materials become bulkier and more indigestible. As plants mature reproductively, NDF content increases. Although our samples were not analyzed for NDF, we recommend that NDF content be analyzed.
Typical NDF values as a percentage of dry matter:
- Percentages of NDF in grass range from the 50s to the 60s. Values above 70% have low forage intake.
- Percentages of NDF in legumes range from the 30s to the upper 40s.
(Cole, n.d.)
As a rule of thumb, the maximum NDF dry matter content of the daily ration should be from 1.2% to 1.5% of the cow's body weight. The higher the quality of the forage, the closer to 1.5% of the cow’s body weight in NDF dry matter can be consumed by the cow. For this reason, NDF values can be used to estimate forage intake. As NDF values increase, forage intake will decrease.
Net Energy Maintenance (NEM) and Net Energy Gain (NEG)
NEM is net energy required for maintenance, and NEG is net energy required for gain. Adjustments in requirements for NEM or NEG are made for various stages of beef cattle production. Most of the previously analyzed forages will meet a cow's energy needs only. For example, the NEM requirement for a 900-pound pregnant yearling heifer in its middle third of pregnancy, with a body condition score of five, and having a mature weight of 1,400, gains 1.5 pounds per day, which requires 0.55 megacalorie per pound (Mcal/lb) on a dry matter basis.
NEM levels for a 1,200-pound mature cow, with milk production of 10 pounds per day, seven months after calving, range from 0.37–0.61 Mcal/lb. This range of NEM levels is also attributable to a 1,200-pound mature cow that is nursing, producing 20 pounds of milk per day, two months after it has calved.
Growing heifer NEG requirements vary based on many factors, the largest being rate of gain. NEG requirements have great variability primarily influenced by the desired rate of gain and finishing weight of the heifer. In general, 700-pound heifers gaining 1.5 pounds per day have a minimum NEG requirement of approximately 0.35 Mcal/lb on a dry matter basis. Energy values can be used to compare forages. Cattle require higher energy levels during lactation and growth. An adjustment in maintenance requirements is made for breed, sex, season, age, hide, temperature, and physical activity. Grazed cattle can have a 10%–20% increase in NEM requirements compared to penned cattle. Research indicates that net energy requirement for steers and heifers is similar when comparing animals of the same body type that are encountering the same stress. It should be noted that cold, wet, muddy conditions also increase energy requirements.
Conversely, bulls can require 12% more energy for maintenance than heifers of the same body type encountering the same stress. Sample 173 Alfalfa/Grass in Table 1 contains the highest energy levels because it has the lowest acid detergent fiber (ADF) levels. As the percentage ADF and neutral detergent fiber (NDF) decrease, the starch and sugar in the feed will increase. Producers wanting to improve body condition scores should consider increasing dietary energy levels.
Phosphorus (P)
Phosphorus (P) levels are generally lower in forages and higher in grains. Samples 173 and 178 in Table 1 are low in P. Requirement for P vary based on the cow’s stage of lactation, growth, and age. Forage levels approaching 0.25% P on a DM basis are at a level of concern. The requirement for most classes of cattle is from .20% to .40% P expressed as a percentage of total dry matter. Be aware that young and rapidly growing calves have a higher requirement, but this need is often met by milk. Phosphorus deficiency can, however, occur in grazing animals. Calcium and phosphorus are generally discussed together because they function together, although the correct ratio of calcium to phosphorus is often debated. Current research indicates that ratios of 1-to-1 and 7-to-1 result in similar performance, assuming that the beef cattle’s dietary P needs are met. Demand for P increases with lactation and is influenced by weight, stage of production, and level of production.
Potassium (K)
A potassium (K) level of 0.6% of the dry matter is considered adequate for beef cattle. Fresh forages are excellent sources of K. Diets containing a high level of concentrates may require K supplementation. The K levels of forages decrease as plants mature. Low concentrations of K are occasionally found in tall fescue during the winter. Potassium may be supplemented in cattle diets as potassium chloride, potassium bicarbonate, potassium sulfate, or potassium carbonate. All forms are readily available.
Ohio forages often contain excessive levels of K in the spring. High K levels have been associated with reduced magnesium absorption. For cattle on pasture, K that has been added for winter mineral supplementation should be removed from the mixture when fescue starts growing in the spring. Fertilizing pastures in the spring with K can also dangerously increase forage K levels above tolerable levels for beef cattle. The maximum tolerable concentration of K on a DM basis for beef cattle is 3%. Sample 158 in Table 1 has a particularly high concentration of K. If grazing this field in the spring, expect reduced absorption of magnesium. More information is available in the Magnesium (Mg) section below. (NRC, 2016).
Calcium (Ca)
Forages are typically high in calcium (Ca), particularly alfalfa hay. The Table 1 samples illustrate this well. Calcium levels on a percentage of DM basis reach the critical level at 0.18% for dry cows. Lactating cows and growing calves will have the highest Ca requirements, needing their DM to have approximately 0.39% of Ca for lactating cows and 0.45% of Ca for growing calves. Sample 225 Orchard Grass in Table 1 is below the recommended level for Ca for some stages of beef cattle production. Calcium serves in the development of bones and teeth. It is also involved in other body functions, such as blood clotting, muscle construction, and the transmission of nerve impulses. The ideal Ca-to-P ratio is 2-to-1, but ratios of 7-to-1 are acceptable. The Ca dietary requirement for most classes of cattle as a percentage of total dry matter is between the range of 0.40%–1.00%. Feeding excessive levels of Ca can create deficiencies of other essential minerals, such as phosphorus, magnesium, iron, iodine, zinc, and manganese (NRC, 2016).
Magnesium (Mg)
A common magnesium (Mg) deficiency occurring in the spring is grass tetany. This problem is usually associated with lactating cows. The initial signs include nervousness and muscular twitching around the face and ears. Magnesium oxide and magnesium sulfate are two common sources of supplemental magnesium that are used to treat this deficiency. Magnesium in dolomitic limestone is a poor source. Magnesium levels below 0.10% are of particular concern for growing and lactating cows. Finishing cattle reach critical Mg levels at 0.2% of DM, while gestating beef cows need their DM to contain 0.12% Mg. High soil potassium levels are associated with increased incidence of grass tetany. The ratio of potassium to calcium plus magnesium should be less than 2.2 to avoid problems with grass tetany [K-to-(Ca + Mg) < 2.2]. Sample 158 in Table 1 has a K-to-(Ca + Mg) ratio of 1.96, so grass tetany is a risk when feeding this forage without magnesium supplementation.
Manganese (Mn)
All samples in Table 1 contain acceptable levels of manganese (Mn). Corn silage is often low in Mn. Manganese is a major component of beef cattle enzymes and serves as an activator of their enzymes. Breeding animals require 40 milligrams per kilogram (mg/kg), and diets containing less than 15.8 mg/kg result in reduced conception rates (delayed cycling). Deficiencies in young animals manifest as twisted legs and enlarged joints.
Sulfur (S)
Sulfur (S) is an essential component of amino acids, B vitamins, thiamin, and biotin. Microorganisms in the rumen can synthesize many sulfur-containing compounds from the amino acid, methionine. The S recommendation in beef cattle diets is 0.15% as a percentage of dry matter. The maximum tolerable concentration is 0.50% (NRC, 2016).
Iron (Fe)
Samples 173, 225, and 178 in Table 1 are low in iron (Fe). In general, most classes of cattle require their dry matter to contain 50 parts per million (ppm) of Fe. The maximum tolerable level of Fe is 1,000 ppm. Iron is essential for red blood cells to transport oxygen. Cereal grain and oil seed meals are common sources of Fe.
Copper (Cu)
Three of the four Table 1 samples are low in copper (Cu). The minimum recommended level of Cu in dry matter is 10 parts per million (ppm). If the forage contains a high level of molybdenum (2 ppm) or sulfur at 0.25%, Cu could be deficient. High concentrations of iron and zinc can also reduce the availability of Cu.
Copper is a component of essential enzymes. Copper deficiency causes reduced growth, anemia, and a change in the animal’s hair coat. Copper can be very toxic to sheep.
Diets that contain excess protein will be high in sulfur and can cause a Cu deficiency. Copper is less available in forage diets than in grain diets. Ideally, the copper-to-molybdenum ratio should be 5 –to-1 or greater (Munshower & Neuman, 1979).
Zinc (Zn)
Zinc (Zn) plays a role in the immune system and is involved in the metabolism of protein and carbohydrates. Zinc deficiencies have been linked to impaired sperm production in bulls. All four Table 1 forage samples are low in Zn. The recommended levels for zinc are between 30 and 1,000 parts per million (ppm) for beef animals. Beef cows require 30 ppm of Zn (NRC, 2016).
The levels of trace elements (Mn, Cu, Zn, and Fe) may have extreme variations in analyzed levels taken from samples of the same lot.
Although the Table 1 forage sample was not analyzed for vitamins, it is reasonable to assume we would need to supplement beef cows with vitamin A via an injection or as an addition to the mineral mixture. Vitamin E may also need to be supplemented. Analysis of the Table 1 forages indicates that only one sample (158) can meet most of the nutrient requirements for our cattle. The three other hay sources will need to be supplemented with a protein source and mineral supplement. Our good-quality hay should be used for cows requiring an improvement in body condition, lactating cows, and growing cows. Analyzing your DM ration will save you money and help to ensure the nutrient requirements of your cattle are being met. Almost all forages should be provided with access to trace mineralized salt. Hay quality is most affected by plant maturity. Early harvest and pasture rotation before seed heads appear will greatly improve the quality of your forage. When determining the mineral source to buy, consider the bioavailability of the nutrients. Mineral supplements containing chelated or proteinate forms of minerals are generally more digestible, while sulfates, carbonates, and oxides are less available to animals.
Relative Feed Value (RFV) and Relative Forage Quality (RFQ)
Relative feed value (RFV) and relative forage quality (RFQ) are two important values used in the evaluation of forages, although neither is used in calculating total DM rations. These numbers give a quick reference for forage digestibility. RFV focuses on predicting the digestibility of forages based on their fiber content. It is widely used to assess the quality of hay, with higher RFV values indicating greater digestibility and nutrient content. On the other hand, RFQ incorporates additional factors, such as protein content, fiber fractions, and non-fiber carbohydrates, to offer a more comprehensive assessment of forage quality. If you have a predominately legume forage sample, RFV and RFQ will be near the same value. On the other hand, forage samples of mostly grass result in a slightly higher RFQ value. Relative forage quality can be used to quickly compare the nutrient concentration of forages. Higher RFQ values mean higher nutritional content.
We would like to thank Dr. Steve Boyles, Ohio State University Extension beef specialist, for his review of this document.
For more information on Ohio State University Extension, College of Food, Agricultural, and Environmental Sciences, Guernsey County, go to guernsey.osu.edu/home.
Additional Resources
Review the following resources for more information:
- Maximizing fall and winter grazing of beef cows and stocker cattle. Ohio State University Extension.
- Nutritional requirements of beef cattle (7th ed). National Academies Press.
- Hay quality designation guidelines. USDA.
References
Cole, E. (n.d.). Understanding your forage test. University of Missouri Extension.
extension.missouri.edu/media/wysiwyg/Extensiondata/CountyPages/Webster/Docs/UnderstandingYourForageTest.pdf
Fluharty, F. L. (2016). Increasing the digestibility of forages = economic benefits! The Ohio State University College of Food, Agricultural, and Environmental Sciences.
u.osu.edu/beef/2015/04/01/increasing-the-digestibility-of-forages-economic-benefits
Hay & Forage Grower. (2023). USDA hay markets – October 31, 2023. Hay & Forage Grower.
hayandforage.com/article-4577-USDA-Hay-Markets-%E2%80%93-October-31-2023-clearcache.html
Munshower, F. F., & Neuman, E. R. (1979). Vegetation on mine spoils low in key nutritional elements. Montana State University.
National Research Council (NRC). (2016). Nutritional requirements of beef cattle (8th ed). National Academies Press.
nap.nationalacademies.org/catalog/19014/nutrient-requirements-of-beef-cattle-eighth-revised-edition