2.3.3. The feed milling plant

Feed milling comprises the following phases:

Receipt of raw materials

This operation consists of receiving the raw materials in bags or bulk. Bulk materials will be stored in silos which must be cleaned before filling. Storage in silos means that the materials can be kept for a long time (several months). For shorter periods, bulk materials may be stored in hangars on the ground in the absence of storage units, avoiding waste and contamination. In tropical regions, silos must be ventilated effectively to avoid fermentation causing degradation of the stored material and even explosions.

Raw materials received in bags will be stored in clean hangars. The bags will not be put on the ground but on openwork floors; they will be piled up properly at a reasonable height in order to avoid collapses causing bursting and wastage. In order to avoid confusion, lots of raw materials will be separated by access corridors which are sufficiently wide to allow handling equipment to .pass. Each lot must bear a sign indicating its nature, origin and date of receipt.

Care will be taken to respect the “first in, first out” principle, which means using the materials in the order that they came in; keeping the raw materials away from adverse weather conditions, sun, pests etc.

Measuring out may be done before or after grinding.

This operation consists of measuring out the quantities of each ingredient according to a formula established by a nutritionist, in accordance with the nutritional requirements of the birds for which the feed is destined.

Weighing in bags is not advised: this is a slow operation with much room for error and wastage.

A metering hopper (mechanical or electronic) is a simple, reliable system enabling bags and bulk materials to be combined; errors are limited and the system is suitable for small units (maximum 5 tonnes/hour).

Grinding

This operation consists of reducing coarse materials to finer fragments with the aid of a grinder. The output of a production unit is often determined by that of the grinder. The output of the grinder depends on the nature (hardness) of the raw materials to be crushed and the diameter of the perforations of the sieve.

Before grinding, cereals collected in the field must be cleaned to remove foreign grains, some of which could be harmful to the health of the stock.

Before going to the grinder, all materials must go through the magnetic separator to eliminate any ferrous elements which could damage the crusher.

Mixing

This operation consists of mixing all the ingredients in the formula: meal and ground ingredients for varying periods as recommended by the supplier of the mixer. A mixture should ideally be homogeneous so that each feed intake by the birds contains all the necessary nutrients. As the size of the particles and the density of the different ingredients is far from identical, the mixing process must be long enough to make the mixture as homogenous as possible.

There are vertical and horizontal mixers. The mixing period varies from 20 to 30 minutes with a vertical mixing screw turning in a shaft; 10 to 15 minutes with a conical screw turning freely; and 5 to 10 minutes with a double action mixing screw (rotary and circular). The duration of mixing for a horizontal mixer with one or two double belt screws is from 3 to 10 minutes.

Extending the mixing period beyond the limits recommended by the builder causes demixing, i.e. the mixture becomes heterogeneous again, separating out according to the density and size of the particles.

The interior of mixers must have easy access (manhole) for regular cleaning. Premixes, vitamin/mineral concentrate and any other additives in powder form will be added directly to the mixer using a hopper designed for the purpose.

An injection of molasses (maximum 6%) or fats may be made into the mixer with appropriate equipment (tank, heater, pump, flow metre, distribution ramp).

Packing

This operation consists of weighing and bagging feed into specially designed 3 or 4 ply paper bags. For long distance transport, new jute bags are stronger. Reusing bags is proscribed for hygiene reasons (transmitting disease from one unit to another).

The feed may also be stored in silos awaiting delivery by bulk lorry. Requires weighbridge to weigh lorries before and after loading.

Pelleting

This operation consists of passing a mealy mixture through an extrusion plate to obtain pellets of variable diameter according to the diameter of the exit holes. Pelleting is done after mixing and requires a range of very expensive equipment (feeder hopper, conditioning tank, press, cooler).

Apart from the high initial investment (almost as much as all the other equipment of the feed factory together), pelleting involves high energy costs, skilled operators and expensive maintenance.

It does have advantages as well. It allows more homogeneous feeding of birds (no selective feeding), reduces wastage, slightly increases the digestibility of the feed, allows healthier feed to be manufactured (reducing the number of germs present) and looks more attractive to buyers.

Choice of site

Usually, choice of the site for a feed factory depends on a balance between raw material supply (areas for producing or storing cereals or cake, closeness of ports, etc) and feed outlets (poultry farming areas). Access routes (roads, railway, rivers) must be taken into consideration when choosing a site.

Production capacity

Units produce anything from 1 ton per day to 15/20 tons per hour.

In the Sahelian zone, depending on circumstances, 2 to 4 tons per hour units producing 400 to 800 tons per month seem more than adequate. Such units can be containerized and easily connected to the electricity grid.

Recommendations

- The production unit must be adapted to the desired objects and not the other way around. Short and medium term needs must be met (3 to 5 years).

- Depreciation of production equipment only represents a very small part of the cost price of the feed, hence the frequent error of focusing attention on the cost of the equipment alone.

- Never lose sight of the fact that the more complete and accurate the data supplied to the builder of the equipment, the more appropriate the plant will be and hence the more profitable the investment.

The choice of a manufacturing design is always a compromise between simple, robust, unsophisticated, easy maintenance equipment with which human errors are common and more sophisticated, more costly, more fragile equipment which is more delicate to maintain but with which the risk of error is almost nil.