Mixing is one of the most important operations in manufacturing of animal feeds and mixer is considered to be the heart of feed milling operation.
The need for uniformity in a complete feed is a must in order to satisfy nutritional requirements of the animal to achieve growth, production and good health as well as to meet regulatory guidelines of food and drug administration.
Those associated with animal feed production realize that if feed ingredients particularly micro- ingredients such as vitamins, amino acids, trace elements and drugs are not properly blended, overall animal performance will be reduced and wide variation within the group of animals will exist. It is also possible to create a toxic situation if some ingredients are not properly mixed. Most feed additives, such as fat soluble vitamins, trace minerals, antibiotics and growth promoters will not perform their intended function if they are not properly blended in the feed.
Further, huge money is spent on storage, and semi automatic or fully automatic proportioning systems to deliver exact amounts of ingredients in a batch. However, if these ingredients are not properly mixed, the quality control system prior to mixer will loose its great deal of effectiveness.
The objective of mixing is to create a completely homogeneous blend. In other words, any sample taken should be identical in nutrient to any other sample. The value of homogeneous blend is very critical for small animals which consume very little feed as compare to large ones. For example a shrimp of 1 gm wt. will require 0.12 gm of feed per day and a day old chick will consume 6-8 gm feed at early stage. Accordingly, if a feed formulation has been properly mixed a 0.12 gm sample of shrimp feed and 6 gm sample of broiler pre starter feed should contain all the nutrients formulated for that diet. Conversely, the value of a homogenous blend for large animals is not as critical as they consume greater quantity of feed say 5 kg to 20 kg per day.
During the manufacture of feeds there are several factors which create or contribute to incomplete mixing. Some of these are related to the machine i.e. type of mixer, design of mixing elements and mixing parameters etc and some are related to the physical properties of the ingredients like particle size, particle shape, density, hygroscopicity, static charge and adhesiveness.
For production of animal feed, three types of mixers namely horizontal, vertical and continuous type are being used. After knowing the advantages and limitations of each design, we can select the best mixer for our specific need.