There are several advantages of pellet feed compared with powder feed for broilers, the main advantage of which is to improve the performance of broilers. Compared with broilers fed powder feed, broilers fed pellet feed require less time for feeding and digestion and have lower body maintenance requirements.
1, the quality of granular material
High quality pellets can be defined as feed pellets that can withstand repeated operations, such as bagging, transportation, storage and feed line delivery without excessive breakage or production of too many fine particles. Particle quality is usually expressed as Particle Durability Index (PDI) and can be measured by tumbling tanks: samples of particles to be examined are first sieved to remove fine powder particles, and then tumbling in the tumbling tanks for a certain amount of time. The tumbled sample is sieved to remove the fine particles, from which the weight of the whole particles can be obtained.
2. PDI calculation formula is as follows:
PDI = Weight of complete particles after rolling/weight of complete particles before rolling x 100
Other equipment can also be used to determine the durability of particles, such as Holman particle detector, wood detector, etc.
Factors affecting pellet quality of feed
3.1 Feed Formula
Some feed components are beneficial for improving pellet quality while others may be unfavorable. Unfortunately, corn-soybean meal diets are not ideal for achieving optimal pellet quality. Because wheat contains higher levels of protein (gluten) and hemicellulose compared to corn or corn by-products, diets supplemented with wheat kernels or wheat by-products (wheat gluten, wheat gluten) have higher grain durability after pelleting. Similarly, partial substitution of oats for corn in the diet can improve the quality of feed pellets. We can rank the beneficial effects of feed grains on feed pellet quality from best to worst: oat, wheat, barley, corn and sorghum.
It has long been known that starch and its gelatinization are the most important factors in achieving optimal pellet quality. However, recent reports suggest that the beneficial effect of protein on pellet quality is far more important than that of starch.
Adding fuel to the diet can adversely affect the quality of feed pellets. This is because the oil encloses the feed particles, which prevents steam from penetrating into the grain, and reduces friction between the ring mold and the feed particles, which in turn reduces the gelatinization rate of starch.
Adding binders (e.g. water (simplest binders), lignosulfonates, hemicellulose extracts, gelatins, etc.) and/or surfactants to diets can improve pellet quality and yield and reduce energy consumption.
Feed Pellet Quality Factor (FPQF) is a tool that can be used to predict the Pellet Quality in Feed formula.
3.2 Particle size of feed materials
Although some researchers have doubts about this, most people still believe that reducing the grain size of feed materials can improve the pellet quality of feed. However, excessive comminution is not recommended to avoid wasting energy and reducing productivity, and it is not conducive to musculogastric development of broilers. On the other hand, rough comminution can reduce the decomposition of feed particles and reduce the gelatinization degree of starch (high gelatinization is required to produce high-quality feed particles).
3.3 Steam conditioning
As the powder passes through the conditioning machine, it is exposed to high-pressure steam. This steam provides the heat and moisture needed for starch gelatinization, allows particles to bond to each other, keeps the feed in a semi-digestible state, and kills pathogens in the feed. The steam temperature and the time of powder in the quencher have great influence on the durability of feed particles. Quenching and tempering of feed at 80 ℃ is sufficient to produce high quality feed granules. In order to produce feed particles with strong tolerance, the minimum time for the powder to stay in the conditioning tank is 30 s. Using the conditioner for a long time (the feed can stay in the conditioner for 3 min to 4 min) can improve the viscosity of feed particles.
3.4 Specifications of ring die/press roll
Pellet feed is produced by pressing hot powder into a ring mold with a press roller. Thicker ring molds (longer ring mold channels) are beneficial for improving the durability of feed particles because it increases the friction time between the feed particles and the ring mold wall, resulting in more complete starch gelatinization. Most starch gelatinization occurs when feed passes through the ring mold. Similar results can be obtained by using a small aperture ring mode. This means that a 60 mm thick ring die is better than a 50 mm or 40 mm thick ring die, and a 3 mm ring die aperture is better than a 5 mm ring die aperture. However, too thick or too small aperture ring mold has a negative effect on particle yield. In addition, increasing the distance between the press roller and the ring mold from 0.1 mm to 2 mm can improve the durability of feed particles.