Evaluating feed components and finished feeds

by Teresa Acklin
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Routine evaluation can ensure safety and quality, as well as optimize the amount of ingredients used.

By Tim Hermann and Scott Baker

   Ingredient quality is the foundation on which an animal ration is built. Therefore, establishing an ingredient quality evaluation program is essential to a successful feed-processing operation. Routine evaluation of finished feed quality will help ensure that proper ingredient storage, proportioning, grinding and mixing are performed.

   Ingredient specifications are essential to a quality assurance program. Specifications serve as the basis for writing purchase agreements, formulating feed rations and performing ingredient inspections. The specifications also provide guidelines for conducting physical, nutritive and drug analyses and for interpreting results.

   Physical and sensory characteristics of coarse grains and ingredients are usually evaluated by the individual who receives or unloads the materials. Important sensory properties that should be examined include product identity, color, odor, texture, moisture, cleanliness (absence of foreign material) and insect infestation.

   Results of this inspection procedure should be compared to reference samples or pre-established standards. Although this appears to be a rudimentary evaluation procedure, sensory checks can prevent the receipt of inferior ingredients or unloading the wrong ingredient because of a shipping error.

   Physical property evaluation also usually involves testing incoming grain and feed ingredients for test weight, bulk density, purity and moisture. All these properties will determine how the material unloads, conveys into and out of bins, stores and processes (either grinding or mixing).

      Nutritional Properties

   Nutritional properties of feed ingredients require laboratory analysis; this usually entails expensive analytical equipment operated by professional chemists. In view of this need, many feed companies send their samples for nutritional analysis to commercial labs.

   A list of feed ingredients and their important nutritional properties is found in Table 1. The frequency of ingredient evaluation will vary according to the mill volume. Evaluation frequency suggested in Table 1 reflects the ingredient usage of a mill manufacturing about 300 tonnes per week and should be adjusted according to production rate, delivery of new batches of ingredients and change in suppliers. The target levels for these nutrients are presented in Table 2 on page 22.

   Many protein testing procedures involve measuring one element, nitrogen, which is present in all protein molecules at about 16%. Protein comprises amino acids, which are the building blocks of protein synthesis. A shortage of protein, or if one or more amino acids are in short supply, will cause animals to experience depressed growth rate, poor feed conversion and reduced reproductive performance.

   Moisture content may be measured directly by weighing the feed ingredient before and after moisture is removed. Drying should be performed in an air oven. Some instruments, which are referred to as moisture balances, will dry, reweigh and calculate moisture content.

   Moisture content is usually expressed on a wet weight basis and can be measured for coarse grains using a moisture meter that measures electrical conductance. Another indirect moisture measurement can be performed using a beam of light in the near infrared (NIR) frequency with a spectrophotometer.

   A high moisture content increases the likelihood of mold and toxin development during storage. High moisture ingredients contain less nutrient value per unit weight, therefore moisture content represents significant economic implications.

   Crude fat content is measured by extracting fat with an ethyl ether solvent and then weighing the extracted fat in a vessel after the solvent has been evaporated. Crude fat is a term that refers to both fats and oils or a mixture of the two and all other organic soluble compounds.

   The melting point of most fats is such that they are solid at ordinary room temperature, while oils have lower melting points and are liquids at room temperatures. Fats are high-energy ingredients containing about 2.25 times the amount of energy as other nutrients. Fat analyses should include moisture, impurities and unsaponifiable material (M.I.U.), as well as free fatty acids (F.F.A.). F.F.A. content should not exceed 15%.

   Crude fiber includes materials that are indigestible to humans and non-ruminant animals. It is defined as material that is insoluble in dilute acid and dilute alkali under specified conditions. Crude fiber is used as an index of an ingredient's feeding value since materials high in fiber are typically low in nutritional value.

   Calcium constitutes about 2% of the body weight and is important for bones, teeth and muscle contraction and relaxation, especially the heartbeat. It has a role in the transmission of nerve impulses, is necessary for blood clotting and activates a number of enzymes.

   Phosphorus is closely associated with calcium, and a deficiency or overabundance of one will interfere with the utilization of the other. Phosphorus is involved with bone formation and maintenance, teeth development, milk secretion and building muscle tissue. Phosphorus is also an essential element in genetic material, metabolic functions, and osmotic and acid-base balance.

   Magnesium interacts with calcium and phosphorus. If extremely low, magnesium will cause calcium to be deposited in soft tissues forming calcified lesions. An excess of magnesium upsets calcium and phosphorus metabolism.

   Sodium helps control osmotic pressure and acid-base balance in body fluids (the transfer of nutrients to the cells and removal of waste material from cells depend on these processes). Sodium is associated with muscle contraction and nerve function.

   Pepsin digest is a procedure used to determine protein digestibility of animal by-product meals. Animal by-product meals are processed under extreme temperature conditions that can cause proteins to become denatured and indigestible.

   Results of a pepsin digest analysis usually are reported as a percentage of pepsin indigestible residue or percent of crude protein that is pepsin indigestible. The Feed Ingredient Guide II published by the American Feed Industry Association recommends that indigestible residue in meat and bone meal should not exceed 14% and that pepsin indigestible crude protein should not exceed 11%.

   Urease is an enzyme present in soybeans that acts on urea to produce carbon dioxide and ammonia. Urease is controlled by heating to denature the enzyme and is analyzed in soybean meal to assess if it has been properly processed.

   All microscopic identification is based upon relating the items seen to known material. Through the use of low magnification (8 to 50 times), materials are examined and identified based on physical characteristics such as shape, color, particle size, softness, hardness and texture. Feed microscopy is a useful method for identifying impurities/contaminants and evaluating the quality of incoming ingredients. Feed microscopy also serves as a useful method for identifying missing ingredients in finished feed.

   Fat sources should be evaluated for M.I.U. components and should not exceed the following levels: moisture less than or equal to 1%, impurities less than or equal to 0.5%, unsaponifiable material less than or equal to 1%.

   Brix is a term commonly used to indicate the sugar (sucrose) content of molasses and is closely related to percent sucrose. The brix analysis is based on the optical properties of the molasses using a refractometer. Brix is expressed in degrees, with a recommended level of 79.5.

      Variance and Information Management

   Permitted Analytical Variation (P.A.V.) guidelines are intended to allow for inherit variability in sampling and laboratory analyses. They are not intended to allow for deficiencies or excesses in a product or poor analytical techniques.

   Table 3 on page 25 lists analytical variances for some common ingredients and explains how to calculate acceptable ranges. If the assay indicates that the ingredient is outside the analytical variance, the feed does not conform to label requirements.

   After investing considerable time and capital to collect a representative sample, have it analyzed and check for variability, the feed processor must manage the information. Correct information management will assist in:

   • detecting ingredient/product variation,

   • evaluating suppliers,

   • determining the discount for substandard product,

   • fine-tuning feed rations,

   • explaining animal performance problems and

   • meeting Good Manufacturing Practices.

   A simple way to use information involves recording laboratory results in table form (either by hand or on a computer spreadsheet program). Columns in the table should include the date material was received, laboratory number assigned to the sample, ingredient supplier and assay results (e.g. protein, moisture).

   Separate data sheets should be kept for each ingredient type (e.g., grain, nutrients and drug). These results should be regularly compared with contract specifications to ensure suppliers are shipping ingredients that meet or exceed quality criteria. Summarize data by month and supplier to detect noticeable trends.

   Another way to summarize lab data is in histogram (bar graph) form. This procedure groups data based on the assay result (rather than by supplier or month). The advantage of a histogram is that it provides a snapshot view of ingredient variability.

   A third way to record and analyze data is in the form of a control chart. This method depicts the amount of variation that occurs over time. Upper and lower limits are used to indicate if a sample is out of tolerance

   The purpose of the control chart is to help identify when to alter or make adjustments during the manufacturing process. For example, when the protein content in soybean meal drops below the lower control limit, more meal should be added to the feed. When the protein content is above the upper control limit, the ration should be reformulated to utilize less soybean meal.

   Feed ingredients should be routinely evaluated to ensure they are safe and contain the correct amount of the specified nutrient and to ensure the finished feed quality will optimize animal performance.

   Tim Herrman is extension state leader, Grain Science and Industry; and Scott Baker is extension assistant, Grain Science and Industry, for the Cooperative Extension Service, Kansas State University, Manhattan, Kansas, U.S. This article is based on work supported under a special project by the Cooperative States Research, Education, Extension service, U.S. Department of Agriculture.

Table 1. Feed ingredients and their analyses

IngredientProteinMoistureFatFiberCalciumPhosphorusSodiumAflatoxinPepsin DigestUreaseMicroscopicBrixFrequency1
Cereal grainXXW
Soybean mealXXXXE
Rice millfeedXXXW
Maize gluten feedXE
Maize gluten mealXE
Meat/Bone mealXXXXXXXXE
Poultry mealXXXXXXXXE
Peanut mealXXXXE
Peanut hullsXXXW
Cottonseed mealXXE
Sunflower mealXXE
Safflower mealXXE
Bakery mealXXXE
1W = Weekly; E = Every load

Table 2. Ingredient profile (in percent)

Maize< 15.0
Soybean meal1
Dehulled 48.0-
Middlings 15.5-17.53.5-4.58.0-9.0
Sun-cured (13%)13.21.933.07.511.0
Sun-cured (15%)15.21.930.07.211.0
Dehydrated (15%)15.22.330.07.5
Dehydrated (22%)
Rice millfeed7.46.726.
Maize gluten feed18.0-24.00.5-1.06.2-7.87.311.0
Maize gluten meal41.0-43.01.0-2.54.0-6.011.0
Methaden fish meal60.011.07.0-11.0
Meat/Bone meal50.410.42.431.
Poultry meal55.0-65.08.0-12.02.0-4.012.0-18.06.0-
Peanut meal247.
Peanut meal & hulls245.
Cottonseed meal41.00.9-3.39.2-13.48.0-10.0
Sunflower meal
Fat< 1.0
¹ Based on solvent extraction of the oil. Mechanical extraction will have 4% fat.
² Solvent extraction of oil.
Source: American Feed Industry Association, 1990

Evaluating feed components

Permitted Analytical Variance.
Table 3 shows analytical variances for some common feed ingredients. The concentration range indicates levels for which the Analytical Variation percentages (AV%) apply; for example, the moisture AV% applies to ingredients containing between 3% and 40% moisture. Using this table, the P.A.V. percentage can be calculated for each ingredient.
Step 1: Multiply the ingredient's expected value by the decimal
equivalent of the percentage or formula shown in the AV% column.
Step 2: Add and subtract the answer to the expected value.
For example, suppose a sample of soybean meal was submitted for protein analysis. If the expected or guaranteed protein content was 44%, the acceptable protein range would be 42.9% to 45.1%.
Step 1:44 x {(20/44 + 2)/100} = 1.08
Step 2:44 - 1.08 = 42.9 44 + 1.08 = 45.1
Table 3. Feed ingredient analytical variations
Proximate Analysis
Protein(20/X + 2)10%-85%954.01/976.05/976.06/984.13
Fiber(30/X + 6)2%-30%962.09/972.10
Ash(45/X + 3)2%-88%942.05
Pepsin digest13971.09
Total sugar as invert1224%-37%925.05
NPN protein(80/X + 3)7%-60%941.04/967.07
Calcium(14/X + 6)0.5%-25%927.02
Calcium12< 10%
Phosphorus(3/X + 8)0.5%-20%946.06/965.17
Salt(7/X + 5)0.5%-14%969.10
Salt(15/X + 9)0.5%-14%943.01
Copper30< 0.03%
Vitamin A301,200-218,000 IU per 0.45 kg 974.29
Vitamin B1245952.20
Riboflavin301-1,500 mg per 0.45 kg970.65/940.33
Niacin253-500 mg per 0.45 kg961.14/944.13
Pantothenic acid254-190 mg per 0.45 kg945.74