Management of pelleting system can help optimize animal performance as well as customer satisfaction in the case of commercial feeds
By Wilmer Pacheco, Adam Fahrenholz and Charles Stark In the last article we discussed different methods to evaluate pellet quality. This month, we will further the discussion by focusing on the importance of pelleting and pellet quality on animal performance. Benefits of pelleting have been well documented and include improvement in average daily gain, feed efficiency, animal uniformity, and feed digestibility. These benefits allow production species to reach their market weight in shorter times and producers to obtain a higher number of flocks or herds in a year. In addition, pelleting reduces nutrient segregation, selective feeding, and microbial load (depending on the combination of conditioning temperature and retention time during thermal processing). One of the main reasons to feed pelleted diets is to increase feed intake. Higher feed intake allows animals to fulfill their maintenance requirements (e.g., respiration, blood circulation, thermoregulation, immune function, etc.) and use the rest of the nutrients for muscle development and meat accretion. As an example, in a recent trial at Auburn University, we observed 17% greater body weight, 12% higher feed intake, and an improvement of 8 points on FCR when broilers were fed pelleted diets in comparison to broilers fed mash diets from 1 to 39 days of age.
With these potential improvement in mind, when pelleted feeds are produced, attention should be paid to pellet durability, percentage of fines at the feeder, and even pellet diameters in order to obtain the maximum benefit of processing.
Pellet durability is the capacity of pellets to withstand repeated handling and arrive intact to the feeder, and quality is the ratio of pellets to fines. And as pellet quality increases, there is an improvement in many of the metrics described above. Poor pellet quality forces animals to spend more time at the feeder, which can negatively affect uniformity. In addition, as pellet quality decreases, there is a greater risk of feed wastage, which can lead to poorer FCR. Furthermore, in the case of poultry, any spilled feed on the litter can serve as a nutrient source for microbial populations, which can lead to higher levels of ammonia and higher incidence of footpad dermatitis.
Pellet durability and therefore quality are influenced by formulation (especially the amount of fat in the mixer), particle size of feed ingredients, temperature, moisture, and retention time during conditioning, die specification, drying and cooling, and throughput. To ensure a good pellet quality, feed mill managers, supervisors, and operators must focus on efficiently managing the pelleting system from conditioning until cooling and beyond. As cool mash enters the conditioner, the energy from steam is transferred to the feed particles, which increases its temperature and moisture. Once the steam condensation takes place on the particle surface, both heat and moisture migrate into the core of the feed particles. Retention time in the conditioner becomes important as the particle size of the ingredients increases, as moisture and heat require more time to be absorbed. In addition, heat and moisture are necessary for starch gelatinization, protein transition and denaturation, particle adhesion, and pathogen reduction. To ensure good pellet quality, feed is typically conditioned at a temperature between 82 and 88°C or 180 to 190°F (with consideration to heat labile proteins and additives), and with a retention time of at least 40 seconds. Another important consideration during feed conditioning is feed distribution within the conditioner; ideally, one section of the conditioner (typically the center) should be full to prevent steam from escaping through the top layer of the feed and condensing on the conditioner wall rather than on the feed. An improper feed distribution leads to moisture differences of the meal entering the pelleting chamber, causing production inefficiencies. After the feed is conditioned, it enters the pelleting chamber where it is compacted between the pellet die and one or more rolls. The effective thickness of the die is important as it controls the amount of work performed by the die on the conditioned mash. Thicker dies (long die channels) have a positive impact on pellet durability by increasing the compression between feed particles and the die wall. A similar result can be obtained by using pellet dies with small hole diameters. Keep in mind that higher effective thicknesses and/or small holes will have a negative impact on pellet mill throughput and overall production efficiency. Reducing pellet diameter typically reduces the open area of the die, which can reduce throughput even if the compression ratio or L/D ratio does not change. Pellet mill preventive maintenance may also impact pellet durability, and so pellet dies and rolls should be properly maintained and replaced as needed. Further, the installation, inspection, and cleaning of magnets in elevator transitions and at conditioner entry are useful measures that can protect pellet mill components by removing tramp metal that can cause hole blockages and/or damage to the working surfaces of the dies and rolls.
Pellets leaving the pelleting chamber are hot, moist, fragile, and easy to break. Successful cooling includes the gentle handling of pellets and adequate heat and moisture removal for safe storage. Remember, heat and moisture must migrate to the surface of the pellet to be removed by the air, so pellet bed depth, cooler discharge rates, and airflow must be controlled to ensure proper cooling. Cooling pellets too rapidly leads to removal of more moisture and heat from the surface of the pellets than from their core, which results in moist pellets with reduced pellet quality. As a rule of thumb, the temperature of the pellets should be no more than 6°C or 10°F above the ambient air temperature and the pellet moisture should be ±0.5% of the original mash moisture upon leaving the mixer. Using thermocouples and/or in-line moisture analyzers in the cooler can help to manage the cooling system (e.g. airflow and pellet bed depth) more efficiently. In addition, an alarm that alerts the operator if temperature or moisture content of cooled pellets rise above a specific threshold can help to correct issues with the cooling system in a timely manner if deviations occur. It is crucial to visually inspect the bed depth on a regular basis as any uneven or excessive loading can result in temperature and moisture differences within the cooler. Bed depth uniformity is very important as variations can create disparities in temperature, moisture content, and final pellet quality of the cooled product.
View instructional video on pellet durability.
The ultimate indicator of the performance of the pelleting system, from samples collected at the feed mill, is the pellet durability analysis. Last year, we created an instructional video which can serve as reference if needed. The purpose of a pellet durability analysis is to simulate the handling of pellets from the feed mill to the farm and to predict the eventual quality of the pellets at the feeder level.
Overall, management of the pelleting system can help to optimize animal performance as well as customer satisfaction in the case of commercial feeds. The most important thing to remember is that manufacturing low-quality pellets may not allow you to convert the investment in pelleting into an improvement in the bottom line.
