Physical Characteristics of Alternative Feeds

The physical characteristics of alternative feeds are not the first thought in the mind of dairy producers, cattlemen or feed professionals as they plan feed rations. It does however have an impact in the decisions that need to be made when planning and designing the on farm feed storage. A discussion of the basic terminology and physical properties of alternative feeds should help the farmer or feed professional recognize the important considerations such as volume of storage required and handling options that need to be addressed in planning for storage.

Feed Terminology

Basic terminology and definitions used in the feed industry are needed in order to accurately describe the types of alternative feeds used in feed rations. There are several sources of official terms including TUYEM(Turkey's Feed Industrialists Association), BESD-BİR (the White Meat Industrialists and Breeders Association) and the Ministry of Agriculture and Forestry of the Republic of Turkey.

This information is used to help communicate the requirements and limitations of transport, delivery, handling, and proper storage of the alternative feed  from its source to the farm.

Physical Form

Physical form describes the physical description of the feed such as a seed or meal and is characteristic of the dimension or size of the seed or particle measured by screening or other processes.


      

  


   Grains are whole seeds from cereal plants.


   Scratch (Chicken  food) are whole, cracked or coarsely cut grain.


Meal (grinded grain) is a feed which has been ground or otherwise reduced in particulate size. Many of the alternative feeds are whole grains, parts of the whole grain, or have gone through some type of processing which may have reduced the particle size.

Screenings (grain screenings) are any material that has been passed through one or more screens which separates various size particles and is obtained from the cleaning of grains.

•    Flakes are rolled or cut into flat pieces with or without prior steam

  Pellets are agglomerated feed formed by compacting and forcing the feed through die     openings by a mechanical process.  Cubes (hay cubes) are similar to pellets, but are larger in   size.

Bulk Physical Properties

The bulk physical property of an alternative feed "as fed" is important to planning and design for handling, transporting, and storing the feed. Different processes occurring during harvest, and manufacturing of a product will impact the physical properties of the end product or by-product used as animal feed.

The variety of feeds used in rations does not allow a comprehensive reference of each feed’s physical properties. Although there are a variety of sources of published information, the published values may vary significantly from the batch of feed delivered to the farm.

Bulk Density

The "bulk density” or "apparent density” is a measurement of a feed’s mass (weight) per unit volume of space the feed occupies. The standard unit is kilograms per cubic meter (kg/m3). Since many suppliers of feed transport feed by weight, the volume of storage space required for a load of feed can more easily be calculated by converting the standard bulk density unit into a volume per unit mass (weight) such as cubic meter per ton (m3 /ton).

Bulk density varies with particle size and compaction (packing) of the feed. Density can vary even in the same batch or lot of feed. To be accurate the density of a batch or lot of feed should be calculated instead of using a published value from a table.

The bulk density is measured several ways. It can be measured by weighing a specific volume of feed and calculating the density. There is an official "test weight per kile” method similar to what is used for corn grain. A simple on site method can be used to get an approximate density.

Settling and consolidating may occur in transport or storage, which compact (pack) the feed. Packing reduces the volume of the feed by reducing the volume of voids or air spaces in the product. This results in a higher “stored” density than a lab test weight or “apparent density”. The packing percentage is available on a limited number of grains from Appel, 1985.

Dry Matter Content (Moisture Content)

The DM content is the amount of DM expressed as a percentage of the total wet weight of the feed. When  the expression  DM (dry matter) ratio is used in relation to a feed, the percentage value of the amount of dry matter contained in that feed is given. For example: For wheat with a DM % of 90, the DM weight obtained with 1 kg. feed weight is 900 gr.

Angle of Repose

The angle of repose is the maximum angle in which a pile of feed will retain its natural slope.

The "filling" angle of repose is the angle measured from horizontal to the pile surface that is retained as feed drops onto the pile. As the feed particles fall onto the pile they may tend to roll and flow (small angle of repose), or hang and wedge together (large angle of repose).

The “emptying” angle of repose is the angle measured from horizontal to the pile surface that is retained as feed is removed from the pile. The emptying angle of repose is also typically called the internal angle of friction. A sharp angle of repose (dried beet pulp, 50°) occurs in a feed that tends to stack and hold together versus a low angle of repose (delinted cottonseed, 25°) for a feed that flows or spreads out.

These two angles of repose are not necessarily the same. The filling angle of repose is usually less than the emptying angle of repose. Published information on the angle of repose of alternative feeds is limited..

Flowability is not a technical term but is a common term used when talking about the appropriate handling and storage method for feeds. It describes the tendency of a feed to flow , which allows it to be handled with conventional conveyors and stored in bins. Many of the alternative feeds will flow to some degree. Feeds such as cottonseed may not flow well which limits the type of storage and handling method that can be used. Cotton seed is generally stored in flat storage and handled by skidsteer loaders or by hand.

Coefficient of Friction

The coefficient of friction between a feed and a wall is the ratio of the normal force and the friction force along the wall surface. It is dependent on the feed stored, and the type of surface in contact with feed.

Engineering Information

Engineering information on physical properties of alternative feeds is limited. It is especially important to have accurate engineering information in designing walls and floors for storage areas. Published data should not be the only source used in the structural design of storage facilities. The supplier should be asked to provide information and experience on the proper storage and handling options for the feed after it is delivered. This may require field measurements of feed properties by the supplier or an agricultural engineer, but this information will be more valuable than published data.

Storage Loads

There are several types of storage loads that must be determined in order to design walls and floors of storage facilities .

The vertical load  of a feed is a pressure measured in kilograms per square meter (kg/m2) that results from the depth of feed stored and the bulk density of the feed. The weight of the feed in storage is equal to the volume of feed times the bulk density.The floor of a storage area must be able to support the vertical pressure or weight of the stored feed.

The lateral load  of a feed is a horizontal pressure on the storage bin wall, which is a result of the depth of feed and the internal angle of friction. As the depth increases so does the lateral pressure. The walls must be designed to withstand this loading without "upping over" or "kicking out” from the floor of the storage.

The friction load is the load on the wall due to the lateral pressure and the coefficient of friction between the bin wall and the feed . The wall must be designed to withstand the compressive load which may crush the wall.

Thermal loads caused by temperature changes can cause dimensional changes between the bin and the stored feed which in tum can cause pressures in the wall. For example a metal bin filled on a hot day will shrink on a cool night and creates a lateral pressure increase between the bin and the stored feed, which can strain the wall.

Moisture effect loads  can cause lateral pressure increases with increasing moisture content of the stored material. Leaks from a roof can cause the stored feed to absorb water and expand which can strain the wall. Feeds that absorb moisture may cake, or set in storage which causes a problem of removing feed, often requiring a rapping of the bin side to loosen feed or the addition of vibrators to loosen feed.

Storage Life

Storage life may be affected by both time and temperature. Most dry products have little problem in storage, but low DM content feeds (i.e., high moisture content) may cause problems if temperatures are also conducive to mold growth. Low temperatures may also be a problem in storage if free water is allowed to freeze. Special storage needs for some products should be discussed with the supplier of the feed to determine the proper handling, type of storage and expected storage life. Spoilage caused by mold and fungi, rancidity of meat and/or dairy products, secondary fermentation, and hot or cold temperatures could all be potential problems if improper storage conditions occur.

When planning for alternative feed storage, asking the proper questions of the supplier in how to properly store and handle the product after it is delivered. Consult an agricultural engineer or consultant to determine what types of structures would be suitable for storing the feeds chosen. Obtain a proper plan for constructing the storage facility. Use a flexible storage facility design to allow for storage of different feeds in the same area.