A Perspective On Mixing And Mix Uniformity: Part 1 - Introduction, Current Situation, Value Of Feed

Keith C. Behnke
Kansas State University

The basic premise used by all nutritionists when formulating rations is that each aliquot (mouthful) of the diet is balanced with respect to the known nutrient requirement of the target animal. The diet must contain the necessary nutrients to support maintenance, growth, production, and health. Feed additives should be present to provide the appropriate level of protection from disease and other maladies. In all cases, the levels must be controlled so as to be neither deficient nor toxic. The question that must be addressed is how well do current feed manufacturing techniques provide that level of nutrient uniformity assumed by the nutritionist?

The basic objective of any feed mixing operation is to obtain a uniform, random mixture of the solid and liquid ingredients in the formula. The equipment used is, at least in theory, designed to accomplish that objective without nutrient destruction in a minimum amount of time. A uniform random mixture can only be obtained if there is no favored direction of movement by individual particles and if there are no selective forces (i.e. centrifugal forces) that come into play. In bulk solids mixing, it is logical that motion must be introduced so that particles are displaced relative to one another. That is a complex way of saying that if solids are layered one on top of another and no motion takes place, mixing will not occur. However, if the container is rolled, shaken, or vibrated, particle displacement will occur and random uniformity will eventually be obtained.

There are obviously many factors that influence mixing and feed uniformity. They can be divided into ingredient characteristics and machine characteristics. For the time being, only bulk solids will be discussed liquids present special circumstances. The purpose of this paper is to provide a discussion of the current situation and provide guidance as to how feed uniformity can be measured.

Current Situation

Mixing is one of the most important operations in the process of feed manufacturing, yet it is frequently given little or no consideration. The objective in mixing is to create a completely homogeneous blend. In other words, every sample taken should be identical in nutrient (attribute) content to any other sample. Needless to say we seldom achieve that goal, however, we do try to manufacture feed that is as uniform as possible.

Too many times too little emphasis is placed on the mixer we use. When we manufacture a feed, we formulate the diet to provide certain nutrients; in fact, we guarantee that many or all of these nutrients are there in the amounts specified. Many thousands of dollars are spent to gather, process, and store ingredients in semi- or fully-automated proportioning systems to feed exact amounts of ingredients to the scale. Yet, if these varied ingredients are not properly mixed, the quality control system prior to that point will lose a great deal of effectiveness.

Value Of Feed Uniformity

Intuitively, the concept of feed uniformity is important and people associated with livestock production realize that if feed ingredients, particularly micro-ingredients such as vitamins, amino acids, trace elements, and drugs, are not properly blended, animal performance will be reduced. Conversely, it is possible to create a toxic situation if some ingredients are not properly incorporated. A recent experience involving urea toxicity comes to mind in which 24 of 25 cattle died because urea segregated from an otherwise safe feed. Most feed additives will fail to provide protection if not properly blended in the feed. Logically, the value of uniformity is greater for the very young animal and animals with a short digestive tract versus older animals that consume large meals less often.

For example, a day-old chick has depleted essentially all nutrient reserves prior to hatching. During his first day on feed, he will consume about ten (10) grams of feed. It is critical that all required nutrients be in that first day’s ration. As an interesting exercise, one can calculate how many 10 gram aliquots are in a three ton batch of starter feed and then contemplate the probability of each being precisely right. Conversely feed uniformity is not likely to be as critical to a finishing steer that is consuming 12 Kg of feed and has a 24 to 48 hour retention time in his GI tract.

Regardless of the target animal, good manufacturing practices dictate that we strive to produce as uniform of feed as is possible. To that end, equipment should be selected based upon known compatibility. Operational protocols should be set to insure that maximum uniformity is obtained. Personnel should be trained and educated on the concept of uniformity and appropriate testing should be conducted to ensure that uniformity objectives are met.


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