Understanding Feed Test Reports
The quantity and quality of feed offered to livestock has a significant impact on livestock productivity, growth and reproductive performance. In addition, feed cost remains the single largest variable cost associated with livestock production. Thus, a properly balanced feeding program is critical to the profitability of any livestock operation.
Balanced feeding programs should supply all essential nutrients at or above required levels and at the same time avoid unnecessary overfeeding of any nutrient(s). The nutrient content of feedstuffs is extremely variable. For this reason, it is impossible to develop a feeding program that will satisfy the animal's nutritional requirements without determining the nutrients supplied by individual ingredients. Feed analysis provides an accurate determination of the nutritional composition of feeds. The nutritional composition of all feeds should be known prior to their use in livestock feeding programs. Labels on commercial feeds provide the necessary information while all other feeds should be analyzed prior to their use in formulating livestock rations. This will allow you to determine what mixture of feeds will best supply essential nutrients at required levels.
This Factsheet is intended to supply information on feed sampling and the various analytical tests which are available from the P.E.I. Soil and Feed Lab.
When and How to Take Feed Samples
To ensure that analytical results accurately reflect the nutritional composition of feed ingredients, samples must be collected properly. To obtain a representative sample, subsamples from several different locations in the lot of feed should be taken. The number of subsamples required willl depend on a number of factors including the variation within the lot of feed. However, in most situations at least 5-10 subsamples will be required. Specialized equipment, grain probes and forage samplers should be used whenever possible. If the required equipment is unavailable, grab samples are acceptable for many feeds. PLEASE NOTE, THAT ONLY CORED SAMPLES OF BALED FORAGES ARE ACCEPTED FOR ANALYSIS BY THE P.E.I. SOIL AND FEED LAB. Subsamples should be thoroughly mixed together , placed in a sealed plastic container and submitted to the lab for analysis as soon as possible. Samples of wet feeds which cannot be submitted for analysis on the day which they are obtained should be stored in the freezer until they can be sent to the lab. Samples of fermented feeds should be obtained after the fermentation process is completed (normally at least 21 days post-harvest) to obtain accurate estimates of pH, ADF, NDF, digestible energy , bound protein and protein solubility
Analytical Tests Available
The P.E.I. Soil and Feed Lab routinely conducts the following tests on feed samples: Dry Matter, Crude Protein, Bound Protein, Soluble Protein, Acid Detergent Fibre (ADF), Neutral Detergent Fibre (NDF), Minerals- Calcium, Phosphorus, Potassium, Magnesium, Salt (Sodium), Copper and Zinc, Crude Fat, Ash and pH. However, every effort will be made to continue to develop protocols for other analytical tests as demands change.
Explanation of Analytical Results
The moisture content of feedstuffs can be quite variable. For example, forages can range from 20-85 % dry matter. To remove variability in nutrient content due to moisture content, all feed results are reported on both "As Fed " and "Dry Matter " Basis. Percent dry matter is determined by removing all the moisture from the feed sample in a drying oven. Portions of the dried material are then used to conduct the additional analytical tests requested. "As fed" values for nutrients are calculated from these "Dry Matter" values by multiplying by the value on a dry matter basis by the % dry matter in the sample.
Crude protein estimates the total protein content of a feed. When measuring crude protein, the nitrogen content of a feed sample is determined . Since proteins contain 16% nitrogen on average, the nitrogen value is multiplied by a factor of 6.25 to calculate the crude protein content of the feed. Since crude protein level includes both true protein (amino acids) and non protein nitrogen, it does not provide information regarding the quality or availability of the protein in a particular feed.
Bound Protein (% of Crude Protein)
When excessive heat is generated during the ensiling process, a portion of the protein is bound to the indigestible fibre fraction. This bound protein is not digested by either the animal or the rumen microbes.
Bound protein measures the amount of heat damaged protein in a feed and can be used to assess the effectiveness of the ensiling process. In general, bound protein levels less than 5% indicate a a good fermentation while bound protein levels in excess of 5% indicate that there has been some heat damage of the protein. The following formula can be used to calculate adjusted crude protein for heat damaged forages:
Adjusted Crude Protein (%) = % Crude Protein - (% Crude Protein x % Bound Protein/100) + 1%
The adjusted protein value should be used to determine the appropriate feeding program.
Soluble protein is that portion of the total protein which is easily solubilized in the rumen and, therefore, immediately available to rumen microbes which convert it quickly to ammonia. In situations where the supply of other nutrients required to transform this ammonia into microbial protein is insufficient, this nitrogen is excreted by the animal as urea through a process which wastes a great deal of energy at the same time. In general, as the soluble protein content of a forage increases, the protein quality is reduced and the amount of rumen undegradable protein ("bypass" protein) decreases. As poorly fermented silages may contain elevated levels of soluble protein and soluble protein can be used to predict "bypass" protein, soluble protein should be determined for each "batch" of ensiled forage.
Acid Detergent Fibre (ADF)
ADF consists of cellulose, lignin, bound protein, and acid insoluble ash portions of a feed. Since these constituents are quite indigestible, ADF is a negative indicator of energy level in forages and grains, i.e., as ADF increases, digestible energy is decreased. Early-cut forages contain less ADF and a more energy than late-cut forages. Legumes generally have lower ADF and a higher net energy than grasses at comparable stages of maturity.
Neutral Detergent Fibre (NDF)
In addition to the components which make up ADF, NDF contains hemicellulose. Since NDF contains hemicellulose, a bulky, more digestible fibre fraction, NDF values are good predictors of dry matter intake. As with ADF, early-cut forages contain less NDF and more energy than late- cut forages. Legumes generally have lower NDF and a higher net energy than grasses at comparable stages of maturity.
Net Energy Lactation (NEL), Digestible Energy (DE) and Total Digestible Nutrients (TDN)
The values reported for NEL, DE and TDN content of forages are calculated from the ADF values, determined through chemical analysis, using the following equations:
Grasses (Dry Matter Basis)
|NEl= 2.45 - (0.032 x ADF)||Maximum = 1.60|
|DE - 4.618 - (0.0573 x ADF)|
|TDN = 114.42 - (1.492 x ADF)|
Legumes (Dry Matter Basis)
|NEl= 2.09 - (0.022 x ADF)||Maximum = 1.50|
|DE - 4.618 - (0.0573 x ADF)|
|TDN = 88.133 - (0.856 x ADF)|
Mixed Forages (Dry Matter Basis)
|NEl= 2.30 - (0.028 x ADF)||Maximum = 1.55|
|DE - 4.618 - (0.0573 x ADF)|
|TDN = 96.038 - (0.032 x ADF)|
Corn Silage (Dry Matter Basis)
|NEl= 2.25 - (0.024 x ADF)||Maximum = 1.75|
Since there are different equations used for the various types of forage it is imperative that the sample be correctly identified. While the ADF content of forages is quite variable, the ADF content of cereal grains is low and quite constant. Therefore, book values for energy levels of cereal grains are normally used for formulating diets.
Minerals are important for bone and tissue growth and repair, milk production and as regulators of body function. The mineral content of feeds is influenced by plant species, plant maturity, soil type and soil fertility. Since the mineral content of forages is extremely variable and the forage contributes a significant portion of the animal's daily requirement for minerals, especially the macro minerals calcium, phosphorus, magnesium and potassium, determining the mineral content of forages is critical to balance rations properly.
During the ensiling process, soluble carbohydrates (sugars) are converted into lactic acid through microbial fermentation. The lactic acid produced causes a reduction in pH which inhibits further microbial activity. Feed pH measures the acidity of a fermented feed and provides an indicator of the effectiveness of the ensiling process.
Ash measures the total amount of inorganic material (minerals) contained by a feed. Since the quantity of ash does not provide information about the amount of any specific nutrient contained by a feed it is often not very useful. However, the ash content of rations for fur-bearing animals as well as fish is used as a quality parameter.
Crude fat is a measure of the total oil or fat content of a feedstuff. The fat content of most traditional feed ingredients such as forages and cereal grains is low and quite consistent. However, the fat content of byproduct feeds such as french fry wastes and oilseeds including, soybeans, can be more variable. When such ingredients account for a significant portion of the ration, it is advisable to have an accurate estimate of fat content to use in ration formulation.