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.
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 dayâ€™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.