Matrix is a term people will generally relate to Keanu Reeves; even google will present you with this as a first-page result. However, the matrix in the feed analogy is more related to something mathematical. The words digestible nutrients of feed ingredients and matrix are generally used as synonyms.  But matrix actually represents the nutrients available in the feed additive together with the nutrients spared or made available by use of the same additive in the feed formulation.  It represents the total nutrition provided to the animal body directly or indirectly by affecting the digestibility of feed. So, what is the use of a matrix? We all remember our schooling days in mathematics and associate with a name called Linear programming problems acronym as LPP. These are mathematical equations to link variables together to extract optimum results. One can set the key parameters such as price, dosage, availability, standards as variables with monetary profits as realistic outcomes. To give an example of LPP, let’s try this, for what combination of three machines A, B and C can work together with efficiency using each other’s limitations on different levels of time, use, power, and accuracy to obtain an algorithm best suitable to manufacture maximum units of D in the least possible time, consuming least electricity and maintaining quality standards by reducing standard deviation. In layman terms, it will give you a method of best utilization of available resources. So a matrix will enable us to use  LPP, which are nowadays coded in software that helps in formulating feed.

So how does one calculate the matrix of a feed additive? The answer is to run digestibility trials. These trials evaluate the nutritional availability of the ingredient to the animal. The availability can be further refined as in the case of terms in energy as gross energy, metabolizable energy, and so on. The digestibility trials also are needed to be refined on the basis of species, age, breed, sex, and diet. A mature broiler breeder will have an ability to digest nutrients from corn which will be different for a layer chick and a corn-soy diet with fishmeal will have a different matrix than a corn-soy-bran diet with lupins. Once individual ingredient digestibility values are calculated the nutritional content can be corrected with these fractions to determine their true potential in feed formulations. Many phytogenic origin products have tried to replace certain high-cost matrix products in the feed. But very few have succeeded to relate the plant-sourced additive in terms of a compatible matrix value. The matrix can be also formed on the basis of growth studies where ingredients for ingredient replacement can be tested by using performance parameters. A correlation graph can be utilized to compare the new ingredients which fit better in an LPP for cost reduction with the old ones, falling short on the price front or other long term frontiers. In the case of certain additives like phytase enzymes which result in mobilization phosphorus, the tibial ash content comparisons are also used to form a matrix.

An in vivo digestibility assay in the case of poultry ideally focuses on an ileal sampling of digesta and deductively analyzing the same with oral fed feed. The birds are sacrificed and digesta is sampled at different levels of the gut to understand the digestibility of ingredients. As ileum is the terminal region of the small intestine and digestion is considered at its optimum here, the feed sampled in these zones is used for developing a matrix. The fecal collection is generally contaminated with renal excretions and is not considered ideal to evaluate digestibility of precision fed feed. The most accurate theoretical method to estimate digestibility values is to use selectorized roosters. Only a few attempts to replicate the digestive values in vitro are successful and are not as accurate as in vivo methods. Most of the values tested in vitro were based on the activity of enzymes on a certain feed grain and do not replicate real-time complexities of in vivo trials.

Research is now moving to the molecular level, and ultimately it is the nutrients that are utilized at a cellular level that matters the most. Current digestibility studies focus on the nutrients absorbed from the intestinal lumen to the blood, whereas growth studies compare the net benefits from the additive. In the future, our goal should be a point of intersection between these two studies with molecular markers used to light up our path to the least cost matrix for success.