Feed Manufacturing and Processing

The principal objective in feed mixing is to assure that an animal receives all of its formulated nutrient allowances every day. Uniformity of particle size and number of particles per unit weight are important considerations for assessing mixing accuracies of the various micro ingredients. Many of the micro ingredients (particularly feed additives) are expensive and elevated levels may be toxic. Thus, a small uniform particle size is a very important criterion in the selection of micro ingredients.

Adjustments Required for Mixing Feeds

Many of the problems in feed mixing are due to differences among feed ingredients in particle shape, size, and density. Feed ingredients with similar sizes and densities tend to blend easily and quickly. For example, ground or cracked grains have densities similar to that of the oilseed meals. Consequently, there is usually very little difficulty in obtaining a uniform blend of these feed ingredients. Minerals on the other hand have densities which are vastly greater than that of grains and oilseed meals. Feed additives have intermediate densities, but very fine particle sizes. Forages have low densities, and highly varied particle shapes and sizes. This diversity of physical form and density of individual feed ingredients complicates the preparation of uniform feed mixes.

Feed additives and vitamins pose a special problem for obtaining a uniform feed mix. Their densities are more similar to that of ground grain and oilseed meals. Thus, uniform mixing should not be so problematic. However, they are included in the mix at very low levels.

This presents a unique problem with respect to spatial distribution. Following a few simple guidelines in feed formulation can minimize the risk of inadequate special distribution of critical micro ingredients.

Guidelines for Mixing Feed

Click here to view a video that explains the guidelines for mixing feed.

Premix

Premix micro ingredients such as feed additives, vitamins, and trace minerals with a suitable diluent prior to their inclusion in a supplement. Diluents serve to dilute the micro ingredient and thereby facilitate the rate of mixing.

Examples of suitable diluents include the macro minerals typically incorporated in a feed mix (i.e. salt, limestone, di-calcium phosphate, magnesium oxide). Diluents should be dry in order to permit a more uniform dispersion of individual micro ingredient particles. Moisture must be avoided as it may cause entrainment and clumping (hygroscopic compounds such as urea are not suitable diluents). The premix (micro ingredients plus diluent) should represent 3%, by weight, of the supplement. Premixing may be done by hand in a large container. However, it can be performed more easily and efficiently by means of a small portable cylinder mixer (cement mixer). Protective clothing, gloves and dust mask should be worn when handling micro ingredients.

Supplement

Prepare a supplement. This supplement will contain the premix, a suitable carrier, and the remaining minor dry ingredients in the diet including minerals, urea, and supplemental protein sources.

Carriers are feed ingredients, which combine, with the micro ingredients in the premix to alter their physical characteristics. By adsorbing to the carrier, the very fine particles of the micro ingredients are allowed to move more rapidly and uniformly through the mix. This rapid movement of micro ingredients through the mix is important to assure adequate distribution prior to addition of molasses.

Carriers should have physical properties comparable to ground grain or oilseed meals. Indeed, both of these may be used as carriers. However, the adsorptive properties of ground grain and oilseed meals are low. This limitation may be overcome by first combining 2% fat to the ground grain or oilseed meal before blending with the premix. The thin film of fat covering the carrier will facilitate adsorption of the micro ingredients in the premix.

Excellent carriers for micro ingredients include poultry litter, rice hulls, wheat bran, vermiculite, alfalfa meal, ground maize cobs, and beet pulp. The amount of carrier to include in the supplement will depend on the “space” available in the diet formulation. The supplement should comprise a minimum of 3% by weight of the finished feed.

In preparing the supplement, first add the carrier, and then add other major ingredients until they reach the central shaft line, then add the premix and other minor ingredients, and finally add the remaining major ingredients. Mixing volume and mixing time will depend on the specifications of the particular mixer being used. Although some mixers will mix feed very efficiently at low volumes, most do not. Review the literature regarding your mixer and then see that the volume of feed being mixed, and mixing times are optimal for the mixer. Be careful not to under fill or overfill the mixer.

Finished Feed

Finished feed may be prepared as follows:

• Add the grain portion of the diet to the mixer;
• Add the dry supplement (remember that the supplement should comprise a minimum of 3% of the finished feed) to the centre of the mixer (if possible, add supplement on the opposite end of the mixer to where the feed is discharged);
• Allow feed to mix for a minimum of 1 minute;
• Add forage component of the diet;
• Add fat component of the diet;
• Add molasses or liquid component of the diet;
• Allow to mix for the time specified for the mixer (usually not less than 8 minutes).

Note: As previously explained, the reason that the supplement is added to the grain portion of the diet prior to the addition of forage is because the grain and supplement have similar particle size and densities. Accordingly, the supplement will distribute itself quickly through the grain. This increased dilution of the supplement prior to the addition of forage and liquid feeds will enhance the spatial distribution of micro ingredients in the complete feed while shortening mixing time.

Adding Molasses

Molasses is a common ingredient in diet formulations. However, it is highly viscous, and this presents several problems in feed mixing. Indeed, if added to the diet improperly it can cause marked increases in the variation of the equal distribution the micro ingredients through the feed mix.

Molasses should be added to the mixer as the last step in formulation. If the molasses is added to the mixture before the supplement has had a chance to mix with the other major ingredients in the diet it may result in entrainment of sequestering of the micro ingredients. This will increase what is called the “Poisson Error” or the variance associated with decreased spatial distribution of micro ingredient particles.

Furthermore, if molasses is added to the mixer before it is adequately filled, it will come in contact with the mixer itself, adhering to the sides of the mixer and moving parts, thereby decreasing mixer efficiency and, necessitating more frequent cleaning. Whereas the obvious challenge with molasses addition to the mix is the formation of feed balls or clumps, the more real problem in terms of animal performance is the potential increase in poor distribution of the micro ingredients if the molasses is not added in the proper order.

Black strap molasses (standardized at 80E Brix) is particularly viscous. The efficiency of mixing black strap molasses with other dietary ingredients will be enhanced if it is first diluted with water (i.e. dilute to 70E Brix).

The viscosity of molasses is markedly reduced by heating. For example, raising the temperature of molasses from 23E C to 27E C (an increase of only 4%) will reduce the viscosity of molasses 50%. Molasses should not be heated to temperatures in excess of 43E C, except for very short periods of time, as this may cause caramelisation.