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Practical evaluation of pellet quality

Dr. Suttisak Boonyoung offers evaluation of pellet quality

Suttisak Boonyoung, Ph.D., Nutritionist, offers insight into pellet quality and its impact on production

Nutrients directly influence broiler and breeder performance. Apart from nutrient factors, pellet quality can also impact production. Generally, commercial feed is produced in 3 main forms including mash, crumble, and pellet. The feed form use depends on the growth phase of flocks and intended purpose (increasing feeding time, bird uniformity, etc.). Pellet quality parameters include physical, chemical, and biological parameters; however, this article will focus on the physical parameters in commercial feed milling. More specifically, understanding the pellet quality parameters, measurements, and guideline values of each feed form.

Mash feed

Mash is the simplest and easiest feed form to prepare. Ingredients are passed through a grinding machine (most commonly roller and hammer mills) to reduce the particle size. Particle size distribution (PSD) and homogeneity are parameters used to determine the mash feed quality. The PSD can be influenced by many factors such as screen size, motor speed, and number of blades and can be determined by many methods. However, the simple and widely used method in most feed mills is sieve analysis. The PSD value is measured using geometric diameter means (GDM) and geometric standard deviation (GSD). The optimum particle size for broilers and breeders should be between 900 and 1500 µm depending on age.

The mash feed homogeneity can be measured by analyzing markers placed in the feed such as iron powder or manganese at different sampling points (at least 10) at specific mixing times. In addition, the homogeneity can also measure the mixer efficiency. These values are used to calculate the mean, standard deviation (SD), and coefficient of variation (homogeneity). The variation in homogeneity must be less than 10% (Table 1).  There are many factors in the milling process that can impact homogeneity, including mixer type (horizontal or vertical mixer), mixing time, and particle size of each ingredient.

Mash feeds used in broiler breeders can increase feeding time and improve flock uniformity. However, nutrient and ingredient segregation, feed waste, and performance (bodyweight, feed efficiency) can be disadvantageous for mash feed. Moreover, energy levels (kcal/kg) should be increased by 50 to 100 kcal/kg in breeder mash feeds because flocks must expend more energy and activity to consume mashed feed versus pelleted feed. Because mash feeds do not receive heat treatment, the risk of Salmonella contamination is higher compared to other feed forms. Other antimicrobial treatments should be considered to control Salmonella in mash feeds.

Pelleted feed

To produce pellets, mash feed is extruded through a pellet die. The pellets then can be cracked into small pieces to produce a crumble feed. The pellet quality is influenced by many factors including particle size, raw materials, pressure, heat, and fat content (Figure 1). For example, wheat-based feeds typically have better pellet quality than corn-based feeds due to properties such as starch and gelatinization temperature making wheat-based diets more suitable for pelleting.

The advantages of pelleted feed over mash feed include fewer amounts of ingredients, less nutrient segregation, less feed waste, easy to manage and transport, and improved performance. Since pellets are heat-treated, the risk of microbial contamination is decreased. In addition, after passing the conditioner, applied steam increases the starch gelatinization and will consequently affect pellet quality and nutrient availability. Inadequate cooling and drying of processed pellets will have a negative impact on pellet quality.

In general, pellet size for commercial broilers and breeders ranges between 3 and 4 mm. Metrics used to evaluate pellet quality include pellet durability, quantity of fines (cracked particles from the pellet), hardness, and appearance. The pellet durability index (PDI) measures the pellet’s resistance to degradation caused by milling, transportation, and farm equipment. The PDI also measures fines that may have a negative impact on diet. Every pellet transfer can decrease durability and increase broken pellet numbers. There are 2 popular methods to measure the PDI. In the tumbling method, pellets (with fines removed) are placed in a tumbling box for a specific time and speed. For example, 10 minutes at 50 rpm. Pellets then are sieved to remove fines and to calculate the PDI. The second method uses a Holmen tester, which is pneumatic. High-velocity air strikes the pellets for a specific time, fines are removed, and the PDI is calculated.

The percentage of cracked pellets and fines increases during transportation from the feed mill to the farm. In extreme cases, the percentage of fines can be up to 50% at the farm, negatively affecting feed conversion. Thus, it is very important to monitor the fines percentage in every process and deliver feedback to the feed mill to improve pellet quality. For a consistent assessment, sieve size for monitoring must be the same between feed mills and farms. Generally, a mesh size of 1,000 µm (No. 18) is used to isolate fines and 2,800 µm (No. 7) is used to determine oversized crumbles (an optional measurement). Fines are quantified at the feed mill before transportation and before loading to a storage bin or silo on the farm. On the farm, fines can also be monitored in the feed track or hopper.

Hardness is the pellet’s ability to resist breakdown due to the pressure and external force. Hardness can also impact flock performance as flocks may refuse feed that is too hard, causing reduced consumption and poor weight gain. If flocks refuse pellets, evaluate the pellet hardness value at the feed mill using a pellet hardness detector. With this machine, 10 pellets are inserted into the device and pressure is increased until pellets are broken. A hardness value is given in kilogram-force (kgf) or Newton (N). (See Table 2 for recommended hardness values.)


Pellet appearance should be evaluated visually and by smell. Characteristics to evaluate include color, odor, and texture. Chemistry can be used for more precise analysis. For example, palm kernel meal can contaminate feed and reduce the protein concentration in the feed. It can be detected visually (black color) and confirmed with chemistry (protein analysis). Likewise, oxidized fat (rancidity) can be detected by smell and confirmed with chemistry.


Pellet quality is an important parameter that significantly influences flock performance. It can be impacted by many parameters such as formula, particle size, and feed mill process. Pellet quality should be monitored starting from the feed mill to the farm because each step can cause a reduction in quality.

Table 1. A comparison of quality measurements of feed forms for commercial broiler and breeder production at different production stages.

Stage Form Quality Measurements
Broiler starter Crumble Fines, PDI, appearance, oversize crumble, proximate composition.*
Broiler grower Crumble Fines, PDI, appearance, proximate composition.
Broiler finisher Pellet Fines, appearance, PDI, hardness,

proximate composition.*

Breeder starter Crumble Fines, appearance, oversize crumble,

proximate composition.*

Breeder grower, layer, male Crumble


Fines, PDI, appearance, proximate composition.*

PSD, appearance, proximate composition.*

*By near infrared reflectance (NIR) in every run and by chemistry in every formula change.

PDI – Pellet durability index.

PSD – Particle size distribution.

Table 2. Pellet quality parameters, equations, and guidelines.

Parameters Equations/Devices Guideline Value
Particle size distribution (PSD) GDM= log-1


wi: mass on its sieve

di: diameter of its sieve


900 to 1,500 µm
Homogeneity (mixability) ()*100


Less than 10 %
Pellet durability index (PDI) Tumbler box/Holmen tester

= Pellet mass*100/Total mass

Higher than 95 %
Percentage of fines Fine mass*100/Total mass Less than 10 %
Appearance Visual and smell observation Color, texture, odor
Pellet hardness Pellet hardness detector 3.5 to 4.5 kgf

Figure 1. Factors impacting feed pellet quality.

Adapted from Reimer, L. 1992. Conditioning. In: Proc. Northern Crops Institute Feed Mill Management and Feed Manufacturing Technol. Short Course. p. 7. California Pellet Mill Co. Crawfordsville, IN.

Dr. Suttisak Boonyoung is a regional nutritionist for Cobb and serves the Asia-Pacific region. He has 13 years of experience in the agriculture and poultry industry. He holds a bachelor’s degree in animal science and a Ph.D. in animal nutrition.


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