Compound feed

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Good quality feed pellets: Does it make sense?

High quality pellets can withstand repeated handling as can occur during bagging, transportation, storage, and moving in feed lines without excessive breakage or generation of fine particles. Here we describe what factors influence the quality.

Feed pelleting can be defined as conversion of finely ground mash feed into dense, free flowing pellets or capsules, in a process that involves steam injection (moisture and heat) and mechanical pressure. There are several advantages for feeding broilers pelleted rather than mash feed. The main advantage is the improved bird performance (improved feed intake, weight gain and feed conversion). Birds fed pelleted diets spend less time and need lower maintenance energy requirements during eating and digestion in comparison to those fed mash feed. The other benefits of feeding pelleted diets include increase feed density, decrease feed dustiness, wastage and selection, better mechanical handling of feed on the feed lines, and destruction of feed-borne pathogens. Therefore, the full genetic potentials of modern broiler strains cannot be achieved without pelleted feed. In order to achieve these multi-benefits, the pellet durability should be of a standard quality (not contain too much fines), otherwise, the bird’s performance will be adversely affected.

Pellet durability index

High quality pellets can be defined as pellets that can withstand repeated handling as can occur during bagging, transportation, storage, and moving on feed lines without excessive breakage or generation of fine particles. Pellet quality is usually expressed as the pellet durability index (PDI), and measured by using a tumbling can device, in which the pellet sample to be tested is first sieved to remove fines, then tumbled in the tumbling can device for a defined period of time. The tumbled sample is then sieved to remove fines, and the amount of intact pellets is determined. The PDI can be calculated as following: weight of intact pellet after tumbling / weight of intact pellet before tumbling x 100. Other devices can be used to determine the pellet durability such as Holmen pellet tester, lignotester, etc.

Factors affecting pellet quality

Several factors have an effect on the quality of the pellets. First of all the feed formulation (raw materials and additives used). Some feed ingredients have a good impact on pellet quality, while others could adversely affect the quality. Unfortunately, corn-soy diets are not the ideal diets to achieve the desired pellet quality. Dietary inclusion of wheat grain or wheat by products (wheat midds, wheat gluten) can increase pellet durability, because of the high protein (gluten) and hemi-cellulose content of wheat in comparison to corn or corn co-products. Similarly inclusion of oat as a partial substitute of corn can increase pellet quality.

We can rank feed grains according to their positive impacts on pellet quality from best to worst as followings:

  • oat,
  • wheat,
  • barley,
  • corn,
  • sorghum.

It was previously known that starch and its gelatinisation is the most important factor for achieving the desired pellet quality. However, recent reports indicated that the positive impact of protein on pellet quality is much more important than that of starch. Dietary inclusion of oil has an adverse effect on pellet quality. This is attributed to the coating effect of oil to the feed particles which prevent their penetration by the steam, also oil reduces the friction generated between die and feed particles with subsequent decrease in the starch gelatinisation rate. Inclusion of binding agents (e.g. water (simplest binder), lignin sulphonate, hemicelluloses extract, gelatin, etc.) and/or surfactants can increase pellet quality, pellet throughput, and lower power consumption (Table 2). The Feed pellet quality factor (FPQF) is a tool used to predict the pellet quality of the feed formula. Estimation of the FPQF for certain feed formula: each feed ingredient has a pellet quality factor (PQF). The PQF has a score from 0 to 10, where 0 predicts poor pellet quality and 10 good pellet quality. We can estimate the FPQF for each ingredient by multiplying the PQF by the % of inclusion of the feed ingredient in the formula (Table 1). The overall FPQF equals the sum of the FPQF of all ingredients used in the formula. Generally, values below 4.7 are indicators for poor pellet quality, while values higher that 4.7 are indicators for good pellet quality.

Table 2 - Examples for extimation of the FPQF for certain formulas

Affect of ingredient particle size and grinding on pellet quality

The second factor influencing pellet quality is the feed ingredient particle size. Although doubted by some researchers, it is accepted that decreasing ingredient particle size has a good influence on pellet quality. However, over grinding is not recommended to avoid power wastage, reduced production rate and suboptimal gizzard development. On the other hand, coarse grinding eases pellet break down and decreases starch gelatinisation (high degree of gelatinisation is required to produce good pellets).

Affect of steam on pellet quality

Processing obviously has a large effect on pellet quality as well. When mash feed passes through the conditioner, it is exposed to high pressure steam. This steam provides the heat and moisture required for starch gelatinisation, particles adhesion, feed semi-digestion, and feed pathogens damage. The steam temperature and the time that mash feed stays in the conditioner have major influence on the durability of the produced pellets. Conditioning the feed at a temperature of 80° C is sufficient to produce good quality pellets. The minimum time that feed should stay in the conditioning tube to produce durable pellets is 30 seconds. Long time conditioners, in which the feed can stay in the conditioner for about 3-4 minutes, can be used to improve pellet stickiness.

Thicker dies have positive impact on pellet durability

Also die/roll specifications should be kept in mind. Pellets are produced via roll pressing of the hot mash against metal die. Thicker dies (long die channels) have a positive impact on pellet durability due to increasing the friction time between feed particles and die wall with subsequent more starch gelatinisation. Most of starch gelatinisation occurs when feed passes through the dies. A similar result can be obtained by using small hole dies. This means that dies of 60 mm thickness are better than those of 50 or 40 mm thickness, and that dies with holes of 3 mm diameter are better than those with holes of 5 mm diameter. However, using thicker or small holes dies have negative impact on pellet throughput. Additionally, increasing the distance between roll and die from 0.1 to 2 mm resulted in an increase in the pellet durability.

The cooler should be taken into consideration.

After leaving the pellet mill, the temperature of the pellets ranges from 70-90° C and the moisture from 15-17%. Proper cooling (via a stream air cooling machine) is required to lower pellet temperature to about 8° C above the ambient temperature, and moisture % to be 12%. The cooling machine can be either a horizontal or vertical type. Quick cooling leads to removal of more moisture and heat from the surface of the pellets than their core, and the resultant pellets will be brittle. On the other hand, prolonged cooling produces very dry pellets that can be exposed to abrasion and can be of low palatability.


Pellet quality can be influenced by several factors, including the ingredients, diet formulation and processing. A good rule of thumb is the pellet quality factor (PQF), that each feed ingredient has. The PQF has a score from 0 to 10, where 0 predicts poor pellet quality and 10 good pellet quality. From experience we know that starch and its gelatinisation is the most important factor for achieving the desired pellet quality. However, recent reports indicated that the positive impact of protein on pellet quality is much more important than that of starch.

References are available on request.

Mahmoud H. Farahat


  • Mariana Alves


    Is it possible to available the references?

    Thank you.

    Mariana Alves, Portugal

  • Emmy Koeleman

    Dear Mariana, here they are: 
    1- Abdollahia, M. R., Ravindrana, V. and Svihus, B. (2013). Pelleting of broiler diets: An overview with emphasis on pellet quality and nutritional value. Anim. Feed Sci. Technol. 179:1-23.
    2- Payne, J. D. (2006). Troubleshooting the pelleting process: in Feed Technology Technical Report Series. American Soybean Association International Marketing.
    3- Payne, J., Rattink, W., Smith, T. and Winowiski, T. (2001). The Pelleting Handbook: A guide for production staff in the compound feed industry. Borregaard lignotech.

  • Dr. Bharat Meena

    This is a nice information for feed millers as well as animal nutritionist.

  • kapoor sonu tandon

    Can we add water to mixter  to increase the moisture  and can we calculate the wt. Loss in feed

  • Mahmoud Farahat, Ph.D.

    Dear Kapoor,
    Yes you can add water in the mixer up to 10 L / ton feed.
    The average moisture content of the feed ingredients in the silos is about 12.6%, while that of the final feed pellets after cooling is about 11%. This means that about 10-15% of the feed moisture is evaporated during feed manufacturing.

    Adding water alone in the mixer can be a partial solution for this problem.Hower, I would recommend adding some forms of surfactants (such as mono and diglycerides) and acidifiers together with water to solve this problem completely

  • Naveen Kumar

    Dear Mr Mahmoud,

    I have some opinion and findings which are in absolute contrast with yours, hope you would enlight: 

    1. We have found that adding water in mixer increases free water proportion in the feed and thus enhances the water activity (Aw) Making feeds more prone nutrient degradation and also to molds 
    2.We have found that popular practice of adding acids mostly propionic or its salt to control mold is of no use as these acids flash point is hardly 52-56 deg C while the normal conditioner setting temp itself is around 80-85 deg C? Propbably we lose all added acids in the feed plant itself?

    3. Further adding surfactant in the mixer reduces the degree of gelatinization (as surfactant stablizes the starch globules and inhibits water molecules penetration, stopping the amylose fractions solublize, which is the most glueing or sticking component of grain starch and has key role in binding feed particles) and hence reduces pellet hardness or PDI. 

    4. Last but the most valid one, can we have the similar engineering calculations and practices for both temperate and tropical world feed milling, where ingredients are so different, ambient temperature is in contrast and logistics are unmatchable?

  • Mahmoud Farahat, Ph.D.

    Dear Mr. Kumar
    Thanks for your comments
    1- If you add water alone in the mixer, most of this water will be evaporated in the cooler during cooling process. However, there is a probable risk of increased mould growth.

    2- It is recommended not to add water alone, but to add it in combination with surfactants and acidifier. There are some commercial products in the global feed additive market that contain surfactants and acidifiers that can be mixed with the water such as maxi mil, fylax, surface, bredol, etc.

    3- Using acidifier in the form of ammonium propionate (buffering propionic acid with ammonium salts) rather than propionic acid alone will enhances its heat stability and decreases its evaporation.

    4- Adding surfactants has been proven to enhance pellet quality. Surfactants reduce water surface tension and improve the homogenization between water and oil content of the feed mix. This subsequently resulted in better distribution of the water particles throughout the feed materials and not only remains in the surface of the feed particles (i.e. binding free water). This for sure will decrease the surface water and water activity (Aw) that accelerate mould growth.

  • Mahmoud Farahat, Ph.D.

    Surfactants decrease the friction generated at the die pores due to its lubricant properties. The advantages of decreasing friction are less power consumption (Kilowatt hours), more pellet throughput and less wearing and tearing of the dies and rolls. Although surfactants partly decrease starch gelatinization of the feed particle outer surface at the die level, it increase the overall starch gelatinization in the conditioner due to sufficient moist heat penetration to the core of the feed particle which accelerate reaching the glass transition temperature and subsequently increase the pellet quality (PDI).

    5- Of course, there could be some degree of variations between tropical and temperate countries. For example, in tropical countries with high relative humidity, the efficiency of pellet cooling may be hindered; therefore efficient cooling machines should be utilized.

    These are some article that could explain what I mentioned in details

  • Phil Mr Rowan

    The surfactants are not cheap so they need / must reduce the Kw/hr per ton are what is the point of adding them, 
    Better to sort the root of the quality problem tham mast it with costly things of limit value.
    Sort the partical grist / mixing cv / conditioning is where the answer normally is.

    Phil Rowan

  • Stefan Omvik

    The Feed Pellet Quality Factor (FPQF) model described in this article was developed by Borregaard LignoTech to help feed producers anticipate problems related to the use of certain raw materials. We have recently also launched an online FPQF calculator - a tool that will enable feed producers to calculate and save the Feed Pellet Quality Factor (FPQF) of their various feed formulations: <a href=''></a>

    Stefan Omvik
    Marketing manager Feed Additives
    Borregaard LignoTech

  • amin amin nahla

    thanks ya kbeer

  • David Gonzalez Sanchez

    Dear Dr. Mahmoud, congratulations for this excellent and explanatory article.

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