Feed analysis reports explained

Introduction

Laboratory analyses of feeds provide the best indication of nutrient availability, allowing feeds to be utilized to their full potential. Reliable nutritional information is important to not only balance rations, but also allows ration balancing programs to determine the most economical ration that will meet the animals' requirements. Although most producers have a good understanding of the concepts of feed ingredients (for example, dry matter, protein, starch etc.), some are unsure of what a laboratory analysis report is telling them. This factsheet will assist producers to have a better understanding of these analytical reports, provide definitions of key terms included in feed analysis reports and provide an example of a laboratory report. Although the layout of reports may be different between laboratories, the parameters indicated are included in most feed analysis reports.

Most producers understand the established concept of crude protein, but modern feed analysis reports will also report the availability of protein as a measure of its digestibility, as well as different fractions of crude protein, including by-pass protein, non-protein nitrogen, etc. Both wet chemistry and Near Infrared Spectroscopy (NIR) are methods commonly used to create an analysis report. Wet chemistry measures the nutritional value using heat and chemicals to break down the forage. NIR estimates the nutritional value of the feed using light reflection rather than chemistry to identify and measure amounts of compounds in a sample. The reflectance values are entered into calibration equations which estimate nutrient values. The equations are based on studies which compare split samples for wet chemistry with NIR reflectance. This provides fast, reproducible and cost-effective results with minimal sample preparation by the laboratory providing the service, and allows for timely return of analytical results for the customer. A sample of a laboratory report for haylage can be found at the end of the factsheet.

Definitions

Dry matter

Each report specifies the dry matter of the feed analyzed. This is the moisture free material left after drying the sample in a laboratory oven. The reason for obtaining the dry matter is because moisture dilutes the concentrations of the nutrients present, and it is standard practice to evaluate the feed and balance rations using a dry matter basis. For the remainder of this factsheet, any numbers mentioned will be based on a dry matter basis for that reason.

Crude protein

Crude protein (CP) is calculated based on the nitrogen content of the feedstuff. Protein is made up of approximately 16% nitrogen, and in the lab, total nitrogen is measured and multiplied by 6.25 (100/16) to report it on a 'crude protein' basis. Generally a corn silage sample will range between 7%–9% CP and haylage 18%–24% CP. What does this tell us? Without looking at the type of protein it is made up of, it doesn't tell us more than that it contains nitrogen, including both true protein that contains amino acids (the building blocks of protein) and non-protein-nitrogen (NPN, like urea and ammonia that also contain nitrogen — urea and ammonia are compounds that rumen microbes can use but they are not directly used by the animal). The report generally splits this parameter down further into soluble protein, Acid Detergent Fibre-CP (ADF-CP), Neutral Detergent Fibre-CP (NDF-CP), and Undegradable Intake Protein (UIP) also known as by-pass protein.

Soluble crude protein

Soluble crude protein is most readily available to animals. This consists of small amino acid chains, or non-protein-nitrogen that will solubilize in rumen fluid, and be absorbed across the rumen wall. Soluble protein is the same whether you look at the 'as fed' or 'dry matter' columns on the feed sheet because it is expressed as a percentage of the total crude protein. Preferably, this number should be between 43%–63% of the CP in corn silage and 49%–67% of CP for haylage. Remember that the soluble protein content increases for corn silage as it ferments, so it is important to regularly test corn silage over time.

By-pass protein

Commonly called by-pass protein, feed analysis sheets often report the fraction of protein that is resistant to degradation by rumen microbes. This fraction also can be called other names like Un-degradable Intake Protein (UIP) and Rumen Undegradable Protein (RUP). This fraction of protein is often valued because it can be absorbed in the small intestine. Before discussing the ADF-CP and NDF-CP, it is important to understand what ADF and NDF are composed of.

ADF and NDF

Acid detergent fibre (ADF) refers to the cell wall portion of the forage, made up of lignin and cellulose. The value is important as it relates to the ability of an animal to digest the forage; a higher ADF suggests a decrease in digestibility. Neutral detergent fibre (NDF) refers to the cell wall fraction that includes ADF and hemicellulose. The NDF value is related to the amount of forage the animal can consume and as NDF increases, the dry matter intake generally decreases. ADF and NDF for corn silage commonly range between 22%–30% and 38%–50%, respectively. For haylage, these numbers range between 30%–39% and 39%–50%, respectively.

ADF-CP and NDF-CP

The ADF-CP is associated with the portion of the CP that is unavailable to the animal as a result of heat damage. In forages this can be natural heating of fermentation, whereas for some feed ingredients, such as distillers' grain, it is the actual heating process that occurs during grain processing. The preferred range is between 0.8%–1%. Within this range, minimal damage has happened to affect the feed quality. Once elevated to 1.5%–2%, overheating has occurred and could mean potential damage to the feed quality, making some crude protein in the feedstuff unusable to the microbes or to the animal.

NDF-CP is similar to ADF-CP, but NDF-CP has some digestibility associated with it. Usually, the NDF-CP is linked to by-pass protein. Meaning that as NDF-CP increases, the more by-pass protein you will have.

NDF, aNDF and aNDFom

More frequently laboratory reports, will specify NDF as aNDF, where the 'a' indicates that amylase, an enzyme, has been used for the NDF procedure. The next extension of that is the aNDFom, where the NDF is 'ash-corrected'. It differs from NDF and aNDF in that it is free of ash, which indicates its value on an 'organic matter' basis (since ash is inorganic). An ashing furnace is used to heat samples to extremely high temperatures, leaving a residue of ash, which only contains the minerals. The ash is then weighed and subtracted from the NDF portion, giving the 'ash-free' NDF or aNDFom.

Why does this matter? When the NDF is determined, residues of ash are often included as part of the NDF value. The variability between NDF and aNDFom varies, as some may have higher ash content due to splashing of soil on leaves from rainwater, areas prone to flooding, or soil picked up during harvest. Ash in haylage ranging between 7%–8% indicates little contamination, 9%–11% indicates contamination, whereas above 11% is considerably problematic. Corn silage ash content varies, but generally the corn is cut high enough that it contains limited amounts of ash due to soil contamination, with numbers ranging between 2.5%–3.5%.

This extra step to obtain aNDFom may delay results, but can be valuable to know when evaluating the feed. Ontario does not have as much need for aNDF corrections as some other areas. However, nutrition programs are adopted from the other jurisdictions and often generate the same type of reports and these numbers are needed to run the program correctly.

Neutral detergent fibre digestibility (NDFD)

The NDFD24 and NDFD48 indicate the number of hours the in-vitro digestibility ran for to determine how digestible the feed source is. In other words, how much of the feed material has been digested by the bugs in the rumen fluid after a set amount of time. For the NDFD24, a number in the 40s is preferred, however the higher the better. This means that within the timeframe of 24 hours, more was digested and indicates that the feed is being used properly by the rumen microbes. For NDFD48, a higher number is ideal as the test has now run twice as long. A number in the mid to high 60s is preferred; some may even see values in the 70s. The NDF disappearance rate is the rate per hour and is based on an equation from Cornell University.

Energy

An equation is used to calculate energy or total digestible nutrients (TDN), since it is not a nutrient. Nevertheless, it is the first limiting parameter for milk production. TDN was based on ADF until Dr. Bill Weiss, at the Ohio State University, developed a new equation, now called the 'Weiss equation' or the 'Ohio State Equation'. This equation includes NDF, lignin, fat, starch, mineral and bound protein and is used to estimate energy values. Here, the NDF-CP is used as a correction factor and on reports often noted by a subscript '*w'.

Lignin

Lignin is the indigestible portion of the plant cell, also known as the glue that holds everything together. This number will increase with the maturity of the forage and usually ranges between 2%–4% for corn silage and 4%–12% for haylage. It is a good indicator of any digestibility issues as lignin negatively affects the digestion of the cell wall by acting as a physical barrier to the microbial enzymes.

Net energy

Net energy lactation (NEl), net energy gain (NEg) and net energy maintenance (NEm) are listed on the report also, but in recent years has generally been derived from all the other components put into a ration balancing program. Generally, the NEg is always the lowest number of the three and should be a number greater than 1. It is looked at mostly by beef producers as they observe weight gain in their cattle as a benchmark. The NEm is generally the highest of the three, although similar in range to NEl.

Minerals

Minerals such as calcium, chloride, phosphorous, potassium, sulphur, magnesium and sodium are also listed. Minerals are categorized between macro minerals (calcium, phosphorous, sodium, chloride, potassium, magnesium) and micro minerals (iron, zinc, copper, manganese, iodine and selenium). Phosphorous (P) levels however create a concern for the environment when fed in excess amounts as it ends up in the manure. Ingredients are evaluated to have a high P digestibility to avoid over feeding and match the animals' needs. Calcium and phosphorous are generally the main focus for beef producers and follow a ratio of Ca:P of 2:1. Monitoring and balancing for potassium level is critical in dry cow rations. However, since most minerals are added at the feed mill via a micro pack, these are not as critical in the individual forage analyzed.

Relative feed value and relative forage quality

The 'relative feed value' (RFV) is not used much anymore, but often still recorded on the certificate of analysis using ADF and NDF in its calculation. RFV was developed by hay producers years ago to market alfalfa based hay. Although protein is not considered in the calculation, generally a higher RFV indicates a higher protein. A RFV of 100 indicates it is decent quality hay, whereas a RFV of 150 is exceptionally good hay. The challenge with this number is that it is okay to use when comparing alfalfa varieties to each other. However, when comparing an alfalfa to a grass, the NDF has a much higher impact in the RFV equation. With fresh clippings of spring alfalfa, the NDF will be in the low to mid 20% whereas at the same point in time, grass would be in the 40% range. This seems fairly high, but in reality, the NDF of a grass doesn't change nearly as much during the course of maturation as that of alfalfa. At harvest, a grass may have a NDF of 52%; similar to where an alfalfa will be at harvest. The value of NDF weighs three times as much, as ADF, in the RFV equation.

Note that there is not much difference between ADF and NDF of alfalfa in spring clippings. For this reason Relative Forage Quality (RFQ) has been created which takes in to account the digestibility of forages. Therefore there is a shift towards using RFQ. For corn silage samples however, the RFQ is not a valuable indicator as corn silage is affected by the concentration of starch, which has a dilution effect.

Fat

Fat reported is a general term but is not really just fat, and should be seen as an ether extract (EE). On some reports it is called ether extract, since it consists of waxes, cutins etc. The range for EE on a corn silage sample analysis usually falls between 3%–4%, and 3.1%–4.6% for haylage.

All report layouts and results will be slightly different. Growing seasons, timing of manure or fertilizer application, harvesting methods, timing and harvesting technique will all affect the nutrient availability of forages. Laboratories update technology, and continue to do their best to calibrate equipment; however small variations may occur. Nevertheless, plenty of reliable information is available for a given sample to aid in precise feeding allowing producers to meet the nutritional demands of the animal.

Looking at this haylage sample (Figure 1) the analyzed values are within expected range for the DM, CP, ADF and NDF. Although the crude protein is in the lower end of the range, it has a noteworthy percentage of 66.72% as soluble protein. Both the ADF and NDF reflect a good digestibility and dry matter intake. The NEl and NEm could preferably be a little higher, but are generally used as a reference as indicated previously. Overall, this forage has good nutritional value based on its certificate of analysis, which is also reflected by the RFQ of 188.3.

While feed analysis reports may seem hard to read they provide a great deal of useful information that can improve production and are worth the investment.

Sample certificate of analysis

This factsheet was written by Anita Heeg, feed ingredients and by products specialist, Ontario Ministry of Agriculture, Food and Rural Affairs, Woodstock.