Feed Formulation Controls Pellet Quality

Many people believe that good feed quality is solely related to nutrition, but physical feed quality also plays a crucial role. It is pointless to have nutrient-dense and accurate feed if the pellets contain too much dust. Fragile pellets will quickly turn into dust, increasing the possibility of wind loss. Research shows that the FCR will increase by 2.4% in broilers fed with 25% pellets + 75% dust, compared to 25% dust + 75% pellets.

Good physical pellet quality will increase feed intake, especially in broiler farming, which will subsequently improve performance. If you are involved in feed production, how often do you receive complaints from customers dissatisfied with the poor physical quality of the feed they receive at the farm? Feed formulation and the grinding process (particle size) contribute 60% to pellet quality, while the remaining 40% relate to the pelleting process (conditioning 20%, die specification 15%, and cooling 5%). Approximately 40% of the quality of pellets is determined by the formulation (including the contribution of raw materials).

Physical pellet quality can be controlled, and it is interesting to say that formulation controls pellet quality. In feed mill QC operations, several parameter approaches are known to measure pellet quality: (1) pellet hardness, (2) pellet durability, and (3) pellet size and shape. Some other minor but potentially disruptive parameters include (1) contamination from other materials and (2) color appearance. These minor parameters are not significant but can affect acceptance by farmers (and poultry). Pellet quality will ultimately be a compromise between quality and quantity. The production department will demand the use of high-quality raw materials to support pelleting efficiency, but the formulation and nutrition department will strive to optimize the use of economical raw materials.

Pellet quality : Pellet hardness

Pellet hardness measures a pellet particle’s resistance to compressive force, indicating how strong a pellet particle is before it breaks or crumbles. The hardness value unit used is usually in Newtons (N) or sometimes measured in kilograms (kgf). Common tools used to measure feed pellet hardness include (1) a Kahl Hardness Tester and (2) an Instron Universal Testing Machine. Measurements are made on individual pellet particles, one by one.

The process involves taking a representative sample of the pellet and placing them in the hardness tester. Apply force to the pellet by pressing a button on the device until the pellet breaks. The device will display the obtained hardness value. This process must be repeated on other individual pellets to get an average value. There is no standard hardness value, but a good hardness level for feed is usually above three kgf.

Another method for measuring pellet hardness is Stoke’s Test, in which a metal ball is dropped from a certain height, and a pellet holder is used to keep individual pellets in place. After the metal ball falls and impacts the pellet, the number of broken pellets is counted to determine the hardness level.

A physical analysis method for measuring hardness, similar to Stoke’s Test, was performed by Edison Saade and Siti Alamsyah (2009) in their research using various types of seaweed as binders in shrimp feed. This method uses a 1-meter-high PVC pipe, and 200 grams of sieved feed pellets (A), free of dust, are evenly placed at the bottom. Then, a 500-gram stone is dropped from a 1-meter height onto the pellets. The pellets are then sieved using a 0.5-mm mesh sieve to remove dust. The remaining pellets (B) are weighed. Hardness can be calculated as B/A * 100%. This method may be more representative as it involves a larger sample size.

Hardness measurement for assessing pellet quality is not popular and is rarely used in everyday quality control practices. Pellet durability is the most common parameter for evaluating pellet quality. The weakness of the hardness method is that measurements are taken on individual pellets, which can lead to bias due to sampling errors, etc. Attempting to involve a large number of individual pellets to obtain a representative sample makes it impractical and time-consuming. Hardness only measures resistance to direct impact/pressure, while durability measures resistance to abrasion/friction during handling. Hardness determines durability, but it is not the only factor, as other factors, such as raw material composition, moisture content, and the pelleting process, also play a role.

Pellet quality : Durability

Durability measures the resistance of feed pellets to damage during handling (within the production system to storage in the feed warehouse) and transportation (impact during loading/unloading and pressure/friction during transport). The parameter for measuring durability is PDI (Pellet Durability Index), expressed as a percentage. Measuring tools include the Holmen pellet tester and the Pfost tumbler.

The test initially begins by evaluating the effects of different raw materials on durability, followed by the development of a standard method for measuring durability by Dr. Harry B. Pfost (1960), known as the ‘K-State method’ or ‘Tumbling Can Durability Test.’ The principle of these tools is relatively the same: rolling pellets into a rotating drum (tumbling can). Inside the drum, partitions are made to create obstacles that increase the frequency of impacts and friction during a specified time. This simple model can be found on the local market.

A 500-gram pellet sample is placed in the tumble can. Ensure the sample is previously sieved to remove dust components so that only pure pellets are tested. Run the machine for 10 minutes. Then, all materials are removed and sieved to separate intact pellets from dust. Usually, a mesh six sieve is used. PDI is calculated using the formula: PDI = weight of intact pellets after the test / initial weight of pellets * 100%. A good durability is > 95%.

Correlation between PDI and hardness

Supriadi, WJ et al. (2021) conducted a study to measure the correlation between PDI and pellet hardness in broiler finisher feed using various types of binders (0% binder, 2% molasses, 2% tapioca flour, and 2% bentonite). The study concluded that PDI is highly influenced by the degree of pellet hardness. The higher the hardness, the higher the durability index.

The simple linear regression analysis yielded a determination coefficient of 0.636, indicating that the relationship between PDI and hardness is 63.6% with a closeness degree of 79.8%. The PDI value obtained is influenced by the effectiveness of the binder in increasing pellet adhesion. The linear regression equation between the two parameters is Y = 92.26 + 0.91 X, where Y is PDI and X is hardness. According to this equation, every 1 unit increase in hardness will increase the PDI value by 0.91%.

Statistical results of regression analysis of the relationship between PDI and Hardness

Regression
Multiple R		0,79
R square		0,64
Adjusted R square		0,61
Standard error		0,55
Regression (significance)		0,00
Variable	Coefficients	p-value
Constanta (a)	92,26	0,00
Hardness (x)	0,91	0.001139

Source: Supriadi, WJ, et al (2021)

The relationship between PDI and hardness was also confirmed in a study by Teixeira et al. (2019), where treatments were based on conditioning temperature (without steam, 60°C, 70°C, 80°C, and 90°C). The treatment without steam resulted in a temperature of 50 °C, which was caused by friction between the die holes. The poorest pellet quality was observed in the treatment without steam (P50) due to the insufficient moisture and pressure required for starch gelatinization. The best pellet quality was obtained with the 90°C steam treatment. PDI and hardness increased linearly with steam temperature, but PDI expressed pellet quality better than hardness due to the larger sample size taken for PDI measurement.

Pellet durability index (PDI), hardness and percentage of experimental feed

	Treatments					SEM	P-value
	P50	P60	P70	P80	P90		L	Q
PDI (%)	78,8	79,0	85,4	87,4	91,4	1,02	<0,010	0,249
Fines (%)	4,49	4,53	4,70	5,12	5,20	0,117	0,734	0,922
Hardness (kgf)	4,32	4,42	5,56	6,26	7,53	0,249	<0,010	0,231

Source: Teixerira Netto et al, 2019

Formulation and pellet quality

Formulation prioritizes the least-cost principle, combining the use of multiple raw materials to find the cheapest combination while still meeting minimum nutritional requirements and the maximum safe limits of raw materials. In addition to understanding the nutritional characteristics of the raw materials used, the formulator must also understand their physical characteristics. Pellet quality depends on nutritional parameters such as fat, crude fiber, and carbohydrates. Therefore, when formulating with respect to pellet quality, many factors need to be considered. The use of binders, whether from raw materials high in starch or additive binders, is one way to ensure pellet quality.

The effect of fat on pellet quality

Chemical components in feed have characteristics that influence the pelleting process and pellet quality. The most prominent is fat, which acts as a lubricant to facilitate pushing pellet particles through die holes, reduce friction, improve the pellet surface quality (smoother and shinier), and reduce pelleting costs (die life, electricity costs). Conversely, if the fat content is too high, it will reduce the physical strength of the pellets, making them more susceptible to crumbling.

To meet the high metabolic energy needs of broiler feed, oil is often added. Oil sources can include CPO (crude palm oil), olein, and others, with additional levels reaching >3%. Vegetable oils negatively affect pellet quality. Fat can also act as a barrier to moisture addition during conditioning. Production processes use a fat coater to spray oil after cooling, reducing the amount of oil passing through the pelleting process.

Water content in feed

Water content in the feed may appear to be unimportant and is rarely considered, but deviations in moisture levels, particularly when feed is too dry, can negatively affect pellet quality. The gelatinization process is greatly influenced by sufficient water availability. Therefore, the moisture content of raw materials must be considered in formulation, as optimal moisture levels will support particle adhesion and reduce energy needs during the pelleting process. Molasses can be added to meet the required moisture levels. Molasses at 1-2% improves pellet durability, partly due to the Maillard reaction, coating the pellet surface.

Recently, it has become quite common to spray a certain amount of water into the mixer as one of the cheapest efforts to improve PDI. Excessive water will have negative effects, such as increasing wet mixing time in the production process, risking contamination of the mixer, increasing the chance of mold growth on pellet feed, and reducing shelf life.

In corn-soybean meal-based feed, where the use of corn is most dominant, the moisture content of the corn is the most important factor to consider. Corn moisture content ranges from 13 to 14%, not exceeding 15% if stored for a long time. Corn that has been stored for a long time will experience moisture loss. After the pelleting process, pellet feed is expected to have a moisture content of around 11%.

Balance of protein and crude fiber

Crude fiber and protein in feed impact pellet quality. In general, the protein and crude fiber in the feed formula should be balanced to enhance durability. High-protein feed usually relies on animal protein sources such as fish meal, feather meal, and MBM. High protein does not support pellet stability because protein has a lower melting point than starch. Eliminating the use of animal protein sources will increase the formula’s cost, so it is wise to use them within safe limits. Not all animal proteins are detrimental to pellet durability, as blood meal, for example, has favorable binding properties for durability. Animal sources contain high levels of collagen, which has sticky binding properties.

Compared to protein, crude fiber tends to be limited, considering that the poultry digestive system has limitations in digesting crude fiber effectively. Crude fiber increases the pellet’s resistance to mechanical damage, but if too high, it will have the opposite Effect, reducing density and pellet strength. Adding too much crude fiber, especially from raw materials that are not finely ground, will cause pellets to break easily, particularly at weak points.

Raw materials with a high crude fiber content tend to be loose and porous inside, absorbing more water. If too much water is absorbed and exacerbated by high temperatures, the pellets will quickly expand and break easily. High-crude fiber raw materials include rice bran and palm kernel meal (PKM). Rice bran is sometimes deliberately contaminated, as husks and sand are often added. These contaminants will not only reduce pellet quality but also cause the silica content to be very abrasive to dies and rollers.

Amylose and amylopectin content

Starch is a carbohydrate reserve in plants and consists of two main polysaccharide components: amylose (20–30%) and amylopectin (70–80%). Both have different structures and physical/chemical properties that affect durability. Amylose has a straight-chain structure, making it denser and forming a stiffer gel when cooled. Amylopectin, on the other hand, has a branched structure that allows it to absorb water more efficiently and has better swelling ability. Amylopectin undergoes gelatinization at lower temperatures, while amylose requires higher temperatures. Amylopectin gelatinization increases adhesion between material particles, making the pellet stronger, while amylose adds structural strength to the pellet, providing additional strength, though not as flexible as amylopectin.

Ideally, a balance between amylopectin and amylose content is required to achieve good durability. This means a high proportion of amylopectin should be maintained to enhance gelatinization and particle adhesion, while sufficient amylose should be maintained to stabilize pellet strength after cooling. Understanding starch characteristics (amylopectin-to-amylose ratio) will help in selecting raw material sources of amylopectin and amylose. The starch content of various raw materials can be seen in the following table.

Comparison of Starch Characteristics (Amylopectin/Amylose) in Raw Materials

Raw materials	Amylopectin (%)	Amylose (%)	Impact on pellet quality
Corn	72-75	25-28	Increases cohesion and strength
Wheat	75-80	20-25	High cohesion, stronger pellets
Potato	80-85	15-20	Very cohesive
Rice (glutinous)	80-85	15-20	High cohesion, high elasticity
Sorghum	70-75	25-30	Balanced cohesion and strength
Cassava	80	20	High cohesion, good elasticity
Barley	70-75	25-30	Good structure, moderate durability
Legumes	60-70	30-40	High strength, low elasticity
Oat	70-75	25-30	Balanced, requires additional binder
Tapioca	85-90	10-15	Very cohesive, high elasticity

Source: Various Sources

Pelleting characteristics of raw materials

Wheat and its derivatives are commonly known as good natural binders to improve pellet durability. They added 10% wheat, which significantly improved the pellet quality. A study by Behnke (1990) used wheat (hard red winter) at various levels to substitute corn and sorghum with factorial treatments using different die thicknesses (38.1 mm and 50.8 mm).

The results showed that wheat significantly improved PDI, where the increase in PDI improvement is linear with the increase in wheat levels in corn or sorghum feed. Compared to wheat’s effect, die thickness significantly improved PDI. Pellet feed pressed with a thick die (50.8 mm) at all wheat levels achieved a PDI >90%, compared to a thin die (38.1 mm) with a majority PDI <80%. Die thickness contributed more to improving PDI than the adhesive effect of wheat.

The Effect of Wheat, Die Thickness, and Cereal Type on PDI of Swine Feed

Die thickness:	38,1 mm		50,8 mm
Main cereal in feed:	Corn	Sorghum	Corn	Sorghum
Wheat 0%	74,5a	76,5a	94,3b	93,4a
Wheat 5%	77,0b	76,8b	95,2a	94,3a
Wheat 10%	79,6b	80,4c	95,3c	95,2b
Wheat 20%	83,0c	86,2d	96,5d	96,7c

Source: Keith C. Behnke

DDGS (distiller-dried grains with soluble) is economical in formulations and is widely used in poultry feed. However, its nutritional quality often varies, especially in protein and fat content, two factors that determine its economic value. Protein content can vary from 24–35% and fat content from 4–10%. Moisture content can also vary, typically ranging from 7.5% to 15%.

Variations are usually due to differences in the proportion of mixing with the soluble fraction (which has a higher moisture content). In the pelleting process, using more than 10–15% DDGS can sometimes reduce pellet quality. If DDGS has sufficient moisture content due to a higher proportion of soluble fraction relative to dried grain, it will support pellet durability. The drying process may also reduce the potential of the natural binding compounds present in DDGS.

The effect of raw material type on durability and process efficiency is determined by its pelleting characteristics. The durability and lubrication characteristics of soybean meal (SBM) are moderate. Given the high inclusion of SBM in formulations, its particle size will also be a determining factor. Meanwhile, the physical quality (particle size) of SBM received can sometimes vary from delicate to coarse, and large contaminants like skins or branches can sometimes be found. SBM, with a particle size of around 900 microns, is ideal for good pellet quality. Coarse SBM, due to high skin contamination, tends to increase crude fiber and decrease fat content. This factor also contributes to pelleting quality and process capacity.

Pelleting Characteristics of Raw Materials Based on Their Effect on Durability and Die Lubrication (0 = poor, 10 = good)

Raw materials	Durability	Lubrication
Barley	5	6
Wheat	8	6
Soybean meal	4	5
Distillers grains (DDG)	3	4
Distillers grain with soluble (DDGS)	5	6
Corn gluten meal (CGM)	5	8
Molasses	7	6

Source: Thomas Winowiski, KSU

Abrasiveness

The abrasive nature of raw materials is crucial, as it significantly impacts the lifespan of pellet mill components like dies and rollers. Abrasiveness refers to the ability to wear down or damage metal surfaces, causing them to wear out quickly. Abrasive raw materials contain hard compounds like silica (SiO3), calcium carbonate (CaCO3), and other minerals like iron, aluminum, etc. Rice husks contain 25% silica, and sand, mainly quartz sand, includes a large amount of silica. Although the crude fiber in rice bran, PKM, and soybean meal hulls is not as hard as silica, it is still abrasive and causes gradual wear on the die and roller surfaces.

Die and roller wear occur due to the high and continuous friction between abrasive materials and metal surfaces. Abrasive particles act like sandpaper, wearing down surfaces. Wear can occur in two types: abrasive wear and adhesive wear. Abrasive wear erodes the surface, reducing the thickness of the die/roller. In contrast, adhesive wear occurs when abrasive particles cause metal material to transfer from one surface to another, resulting in deformation and further damage. High friction causes temperature increases, which in turn softens the metal surface and accelerates the wear process.

Based on their abrasiveness, raw materials are classified into four groups: very high, high, medium, and low. Limestone has very high abrasiveness due to its calcium carbonate content. When used in high percentages, it significantly reduces the lifespan of dies and rolls. The quality of rice bran varies greatly depending on the mixture of husks and broken rice. Rice bran abrasiveness is related to husk contamination (>15%), classifying it as highly abrasive. Soybean meal and PKM are categorized as medium abrasives, but at high usage levels, they can accelerate die/roller wear. Corn is classified as low abrasive, with softer crude fiber compared to other high-fiber raw materials, making it less abrasive to metal surfaces.

Use of binder

Substituting some proportion of corn with wheat or its derivatives (e.g., wheat flour) improves pellet quality. Conversely, when considering price, replacing wheat/wheat flour with corn yields a different pellet quality. To maintain it, or in feed types where durability and hardness are critical factors, binders are often chosen. Binders are additives used in small amounts to enhance pellet durability and hardness. They are divided into two categories: synthetic binders and organic binders.

Binders contain adhesive elements that increase the cohesion between feed particles, making them easier to unite and form compact pellets. Binders can also create a thin film on particle surfaces, protecting them from damage during handling, keeping the pellet compact, and reducing dust formation. While synthetic binders are produced through chemical processes or industrial engineering, organic binders come from natural sources (plants, animals, or minerals).

Synthetic binders have stable and consistent physical and chemical properties, while organic binders have more complex and variable compositions but are environmentally friendly. Lignosulfonate and bentonite are popular organic binders. Examples of synthetic binders include HPMC, polyvinyl alcohol, and urea-formaldehyde resin. Using binders will increase feed costs because they have no nutritional contribution, but the formulator will compromise this with other benefits and considerations.

References

Edison Saade dan Siti Alamsyah. [2009]. Uji fisik dan kimiawi pakan buatan untuk udang windu Penaeus monodon Fab menggunakan berbagai jenis rumput laut sebagai bahan perekat. Jurnal Ilmu Kelautan dan Perikanan, Vol 19 (2) : 107 – 115.

Ioannis Mavromichalis. [2023]. 7 ways feed formulation can improve pellet durability. Feed & Grain. Online magazine.

Keith C. Behnke. Feed pelleting reference guide. Section 5: Pellet Durability. Chapter 19: Factors affecting pellet quality. Kansas State University.

Mohammad Hossein, M. Ghasem Abadi, H. Moravej, M. Shivazad, M A Karimi Torshizi, and Woo Kyun Kim. [2019]. Effect of different types and levels of fat addition and pellet binders on physical pellet quality of broiler feeds. Poult Sci 98(10) 4745-4754. 

Ramesh Subramonian. [2017]. Impact of feed raw materials on pellet quality. Borregaard SEA.

Supriadi, W.J., I. Amal, J. Mustabi, J.A. Syamsu and M.F. Latief. [2021]. Relationship between pellet durability index and hardness of pellet with various binder for broiler finisher phase. Fac. Of Animal Science, Universitas Hasanuddin Makassar. IOP Conf. Series: Earth and Environmental Science 788 (2021) 012061.

Teixira Netto, M.V, A. Massuquetto, E.L. Krabbe, D. Surek, S.G. Oliveira, and A. Maiorka. [2019]. Effect of Conditioning Temperature on Pellet Quality, Diet Digestibility, and Broiler Performance. The Journal of Applied Poultry Research 28(4). June.

Thomas, S. Winowiski. Binding and other functional characteristics of ingredients. Kansas State University.

Thomas, S. Winowiski. Pellet quality in animal feeds. Ligno Tech USA, Inc.