Literature review on the influence of milling and pelleting on granulation and physical characteristics, and production cost of pelleted poultry feed

Transcription

1 Master s Thesis ECTS Department of Animal and Aquacultural Sciences Literature review on the influence of milling and pelleting on granulation and physical characteristics, and production cost of pelleted poultry feed Stojan Milanovic Feed Manufacturing Technology

2 Master thesis in Feed Manufacturing Technology Norwegian University of Life Sciences Faculty of Biosciences Department of Animal and Aquacultural Sciences Title: Literature review on the influence of milling and pelleting on granulation and physical characteristics, and production cost of pelleted poultry feed. Supervisor: Professor Trond Storebakken Student: Stojan Milanovic 1

3 Contents Abstract... 3 Acknowledgments Introduction Historical development of animal feed Literature overview Feed for animals Grinding Hammer mill Factors affecting grinding result by the hammer mill Roller Mill Basic roller mill Effect of grinding method on broiler performance The pelleting process Important advantages of pelleting: Important features of the pelleting process Chemical composition of pelleted material The mechanism of digestion in poultry Anatomy and Function of gizzard (grub) Influence of the structure of the mixture on the development and functioning of gizzard (grub) Effect of particle size on digestive tract development and physiology The optimal structure of feed for poultry The effects of increasing the share of large particles in mixtures for poultry Effect of particle size and particle size distribution on performance of poultry Effect of particle size on pellet quality and feed production economy Effect of particle size on pellet quality Effect of particle size on energy cost in feed processing Discussion Mash feed Pelleted feed Effect of physical form of feed - mash versus pellets Manufacturing cost energy consumption Conclusions References

4 Abstract The major objective of poultry feeding is the conversion of feedstuff into human food. The economic importance of poultry feeding, becomes apparent when it is realized that 60-70% of the total production cost of poultry production is feed. For this reason, the efficient use of feed is extremely important in broiler production. The objective of this research was to review connections between grinding and the pelleting process, and to describe how digestion processes in poultry were influenced by mash or pelleted feed. This literature showed that that energy consumption is a highly relevant factor of economy of feed industry, and that it is affected by grinding. Thus, main criterions for evaluating optimal particle size in feed were both biotic and economic factors. Comparisons were done with mash and pelleted feed. Mash diet gives greater unification of growth, lower mortality and requires lower use of energy, making it more economical. Poultry has preferences for bigger particles size, so pelleted feed increases feed intake relative to mash. Pelleted feed also results in lower percentage of waste in feeding, and is also easier to handle, transport and store. On the other side, pelleted feed is about 10% more expensive than the other which are not pelleted, largely due to higher energy consumption during production. Recommendations regarding optimum particle size, however, have been contradictory, as the results from feeding trials and different experiments are confounded by a number of factors, including feed physical form, complexity of the diet, grain type, endosperm hardness, grinding method, pellet quality and particle size distribution. On each of this factors possibilities to influence on them are always existing. On the end, however, pelleted feed seems to have more advantages than disadvantages. However, opinions presented in the literature are divided, so more researches is needed to finally conclude which is optimal, mash or pelleted feed. Keywords: Grinding, pelleting, mash feed, pelleted feed, energy consumption, poultry, gizzard 3

5 Acknowledgments I wish to thank my supervisor professor Trond Storebakken for all advices and good words, especially positive energy and life guidance. I would also like to thank to Ismet Nikqi and Dejan Miladinovic, for their patience and useful comments, and shared experience. On the end, I would like to thank to my family and friends for their moral support and encouragement throughout my study. 4

6 1 Introduction 1.1 Historical development of animal feed Until two centuries ago, little attention was paid to animal nutrition. Monogastric animals were left to search their own feed, or they were fed often from food production. With mechanization of agriculture and increase of production efficiency during the 19th century, cultivation and use of agricultural products for animal feed became increasingly common (Đorđević and Dinić, 2011). In addition to increased mechanization of agricultural production in mid of 19th century, breeding and the creation of productive races, first horses, then cattle, and particularly pigs and poultry increases the demands for feed quality. Along with this, it exceeds from pasture feeding to manure feeding, which is considered as one of the most important changes in livestock production (Bekrić, 1999). In the first half of the XX century farm animals were fed with large quantities of grains, with small amounts of protein. Over time, research in the field of animal nutrition progress thus and enabled more precise definition of the composition of the meal, mixing all ingredients in a mixture became common (Ewing, 1951). Modern cattle farming is characterized by well-organized production, and under such conditions, nutrition has a crucial influence on the quantity and quality of animal products (meat, milk) as well as on the economy of production. New races and types of domestic animals with higher productivity require proper and controlled diet in order to express their genetic potential (Đorđević et al., 2009). These changes have set new requirements in terms of preparing feed for the animals, and gradually moves to preparation of a mixture that will fully satisfy the nutritional needs of animals. The objective for this thesis work is to review relevant literature with focus on a key area in processing pelleted feed for monogastric animals, namely particle reduction in pelleted and mash feed for monogastric animals (focus is on poultry), how different particle size are influencing on animals growth and health, and how to combine all that factors to get economically costeffective and sustainable production of feed. 5

7 2 Literature overview 2.1 Feed for animals Industrially produced complete feed for poultry and swine contain a higher number of ingredients which needs to be homogeneously mixed. To make that possible, most of the ingredients which are obtained in the feed mixture needs to be grinded. Fragmentation enables homogeneous mixing of raw materials. This reduces resulting mixture to a stratification and facilitates pelleting. Fragmentation also increases the specific surface area of the mixture of ingredients and thus improve their utilization in the intestinal tract of animals (Behnke, 1996; Koch, 1996). For this reason, fine grinding is regarded as a key factor to achieve a high growth of animals. However, it is increasingly recognized that vulnerability of farm animals grows with the genetic progress, and fine grinding can cause health problems and decrease growth of poultry (Taylor and Jones 2004; Svihus, 2011). The consequences of the use of too fragmented feed in the diet of cattle were increased glandular stomach (proventriculus), and pancreas, as well as insufficiently developed grub (stomach muscle) which adversely operates on the health and growth (Taylor and Jones, 2004). The grub of poultry is equipped with powerful muscle contractions which lead to the fragmentation of feed particles. The presence of large particles stimulate activity and development of grub. A well-developed grub increases volume and capacity of the digestive tract, and leads to a longer period of feed to stay in the stomach (Svihus, 2011). This contributes to better utilization of nutrients and lower the ph value of the material in the stomach (Duke, 1992), reducing the risk of coccidiosis (Cumming, 1994), and lead to the destruction of pathogenic microorganisms potentially presented in the feed (Engberg et al., 2002). It has been found that the coarse particles can be completely fragmented by the grub (Hetland et al., 2002), and that this fragmentation does not affect the speed of passage of feed through the gastrointestinal tract (Svihus et al., 2002). This suggests that from a nutritional point of view, grains can be coarsely grinded, leading to a reduction in energy consumption and an increased capacity of milling devices (Svihus et al., 2004b). In pig farming, animal health and especially health of the gastrointestinal tract, is highly important area of modern research. Suitable granulation of feed can be a cheap way to positive effect on the health of the gastrointestinal tract (Klausing, 2011). In swine nutrition finer grit is preferred compared with granulation of poultry feed because the pigs have difficulties in digesting coarse 6

8 particles (Klausing, 2011). However, too fragmented feed have shown a negative action in breeding pigs. A study by Klausing (2010), compared coarse and finely minced feed for pigs. It reported a significant reduction in the presence of bacteria of the genus Salmonella by using large grinded feed. Granulation of feed is important both in terms of stomach ulcers and other damage to the stomach which has been found to be less common in pigs fed by coarsely grinded feed. Thereby, it s also shown that most important is to reduce content of fine particles on minimum (Cappaii al., 2013; Ball et al., 2015). Treatment of ulcers in the stomach and other damage caused by the presence of small particles of feed, is complicated, expensive and often ineffective, and may lead to major economic loss (Frendship, 2003). Accordingly, since the coarse particles are poorly digestible, and that the fine particles have a negative effect on the stomach of pigs, it is desirable that the share fractions of medium size is as large as possible. In modern rearing of poultry and pigs, mixtures are rarely used in powder form but mainly pelleted after the mixing process (Fahrenholz, 2012). Pelleting represents agglomeration process (connecting) particle feed under pressure, humidity and heat, to give the agglomerates forms of rollers called pellet (Skotch et al., 1981). Use of pelleted feed, in addition to other benefits, contributes to better production indicators in animal s terms of average daily gain and better feed conversion compared with the use of powder feed, which is found in poultry (Calet, 1965) and in pigs (Jensen and Becker, 1965). The desired granular composition can be achieved by milling the ingredients, above all cereals which are the most common ingredients. However, during the pelleting process, an intensive comminuting the particles so that it disrupts granulation of the mixture obtained after grinding and mixing (Engberg et al., 2002; Svihus et al., 2004b; Amerah et al., 2007; Abdollahi et al., 2011). The pelleting process results in an almost complete elimination of coarse particles, and formation of large quantity of fine particles. From the point of feeding poultry, there were attempts to coarser grinding the cereal mixture components increase the share of large particles in the pellet. Thus, in the research conducted by Hetland (2003), as well as a Svihus et al. (2004a), it was shown that in extreme cases the particle size before pelleting (wheat as cereal component of the mixture has gone through pelleting minced), the pellet press will not grind coarse particles completely. This suggests that, if the desire is to increase the amount of large particles in the pelleted mixture, in which the 7

9 predominant ingredient is corn (Balkan countries), the corn must be grinded coarser (roller mill), than what is seen with the hammer mill. 2.2 Grinding Grinding is done because of necessity to mix several of ingredients with a satisfactory level of homogeneity of the mixture. In the manufacture, feed mills represent one of the basic operations. In fact, more than 80% of the raw materials used for the production of animals, needs to be grinded (Đuragić et al., 2002). Grinding is done, above all, for all kinds of different cereals, and byproducts of agriculture and feed industry (meal, cake and mineral nutrients). The structure milled product, whether it is on the individual components or finished mixtures, must meet the physiological requirements of the animals. The finer particles are, the greater is their specific surface and easier operation of the digestive enzymes of animals (Đuragić et al., 2002). The digestive systems of different animal species have different capacity for degradation of feed components, which is why they require a different degree of fragmentation. Also, within the same animal species, there are different needs in terms of the degree of fragmentation, depending on the age of the animal. Cattle and sheep have a long and complex digestive system and feed particles don t have to be small. The degradation of starch in the stomach of these animals should be as small as possible for the sake of antagonizing rumen acidosis, which can be achieved by grinding coarser grains (particle size is half or a quarter of the grain) (Ziggers 2001). Pigs have a short digestive system (like man), and need fragmented feed. Poultry has a short but complex digestive system, facilitating more usage of coarsely grinded feed compared to pigs. (Sredanović et al., 1997; Ziggers 2001; Đuragić et al., 2002; Koch, 2002). In addition to the physiological requirements of animals, the particle size is important for optimum performance of the following technological operations (mixing, pelleting, expanding, extruding) (Wild, 1992). Grinding facilitates mixing of the various components that are constituted in the mixture and contributes to greater stability of the mixture, due to lower propensity towards layering of the various components (Koster, 2003). Finer grinding means greater specific surface area of particles, causing the material to absorb a greater amount of water during preparation for pelleting, and this will increase the degree of starch gelatinization, which contributes to a better linking of particles in the pellet. Finer grinding leads to a better pellet quality, with reduction of air space between the particles, and allowing better contact of particles in the pellet (Koster, 2003). 8

10 Mincing of the different components included in the composition of feed, can be done by using different types of mills, but the use of a hammer mill and roller mill is most common (Ziggers, 2001). Table 1. Comparison of a hammer mill and roller mill (Wild 1992) Characteristics Hammer mill Roller mill Particle size Small to big Medium to big Span particle size Wide Narrow Specific energy consumption High/very high Low-pitched Loss of moisture due to heating Substantial (10-15⁰C) Insignificant (4⁰C) Aspiration Needed Not needed Handling Simple Complex 2.3 Hammer mill A hammer mill (Fig. 1) consists from of a steel frame in which is placed rotor. In the rotor are several rows placed hitters (hammers), which can be fixed or free hanging. Hammers are narrow and made of high quality steel (Svihus, 2009, HFE 305 course). The upper and lower end are drilled holes which are made for fixing so that the hammer can be fixed to both ends. When the impact side is used up, the hammer is turned on another side or it changes the direction of rotation of the rotor and so the other side becomes striking force (Miladinovic, D. Pers. comm.). When one side wears up, the hammer can be turned and used as twice more. The intensity of outlay depends from the material that needs to be grinded and from the specific loading of milled material, expressed by material weight per time unit (Kersten et al., 2005). The distance between successive hammers, placed in the same order, are determined by using differential rings. The number, length, width and strength of hammers depends on the type of material that needs to be grinded and for needed granulation (Koch, 2002, Kersten et al., 2005). The grinding chamber is limited by a steel screen, which can be changed. Sieves which have openings determines the size of the granulation grist (FAO, 2013). In the upper part of the chamber, an impactor plate, to which hammers throw material, can be. It is mandatory to incorporate one or more magnets to prevent the entry of metal particles in the chamber of the feeder system of the 9

11 hammer mill. Their presence could cause damage to the operating elements of the hammer, as well as the emergence of sparks that can cause an explosion in a suitable concentration of dust (FAO, 2013). Below the sieve is receiving hopper for the material in which it is installed opening for aspirated air. The opening can contain adjustable lid which can regulate the intensity of aspiration. From the receiving bin, material can still be carried with most common, worm conveyors or pneumatic transport (Kersten et al., 2005). Figure 1. Basic hammer mill (Koch, 2002) Mulching in a hammer is induced by two forces. The first is the impact force. When material gets into minced chamber, hammers are moving at high speed and hitting the particles which leads to fragmentation (Svihus 2009, HFE 305 course). Also, hammers are throwing particles on the surface of the sieve and shock plate. Due to high speed the hammer is forming a curtain of material in the form of a ring between the tip of the striker and the screen surface. Particles near the hammer (inside of the ring) are accelerating, and the particles in the outer parts of formed rings are slowed down by sieve and form layers with different speeds of particles. Particles velocity is decreased, as the layer is closer to the sieve, and it reaches sufficiently low output speed. Particles are passing through the openings of the sieve if they are less than the diameter of holes in the screen (Svihus 2009, HFE 305 course.). The second type of force that leads to fragmentation of particles in the hammer chamber is the force of friction. These forces are occurring in particle contact with the 10

12 screen surface and lead to more fragmentation and also rounding of particles. Therefore, on the receiver of hammer mill particles are considerably more regular shape (spherical particles) in relation to other methods of comminution. In order for particles to leave minced chamber it is necessary to reach a certain output speed. In the case that the velocity of the particles near the sieve are too large, although the particles are less than the diameter of holes in the screen, they continue the circular motion and come up with excessive grinding, excessive wear of hammer and heating of materials (Miladinovic D., Pers. comm.). Exit of particles supported by the current aspiration of air, that draws enough chopped particles through the sieve openings. Particles that passes through a sieve and fall into the receiving hopper are then transported either mechanically (worm or chain conveyors) or pneumatic transport (Heiman, 2005; Kersten et al., 2005; Anderson, 2007). On the effects of fragmentation, affects type of materials that needs to be grinded (physicalchemical, and structural and mechanical properties) and the grinding parameters. With the increasing strength and elasticity of the particle, grinding capacity decreases and energy expenditure increases (Kersten et al., 2005). Important parameter of grinding at hammer mill is the circumferential velocity of the striker. When the speed increases, particles that have already been chopped to a size which is desired, they have less time to go out through the sieve openings because they will quickly come to next hammer. This causes excessive fragmentation and longer retention of material, hence lower capacity devices and higher specific energy consumption. It is therefore, highly important to set extensive optimal speed of hammers. In the case of too high fragmentation of materials, it is economically favorable to reduce the extensive speed of the striker than to increase the size of mash screen. For maximum energy savings, it is recommended to go for minimum value of the rotational speed, which achieves a satisfactory degree of fragmentation (Ruetsche, 1989) Factors affecting grinding result by the hammer mill The type of cereal matters when it comes to grinding efficiency, as more fibrous cereals are grinded less efficiently than other brittle cereals. For most common cereals used in feed production the grinding efficiency declines in this order: Corn Wheat Barley Oats (Svihus 2009, HFE 305 course). Moisture content of grains has a big influence on final grinding result. Thus, high moisture level in the grains can result in higher energy consumption during grinding. Moreover, technical properties of hammer mill significantly influence the grinding efficiency. For 11

13 instance, the number of hammers (usually 4-8 rows of hammers) is proportional with through output rate but inversely proportional with particle size. This means that increased number of hammers will result in higher grinding speed but finer particles. Grain particles, thus, are likely to get higher impact (hits) as the number of hammers is increased. Hammer speed should not be higher than a certain limit. Increased or decreased speed may lead to deviations from target particle size (Svihus 2009, HFE 305 course). However, we can control grinding by adjusting hammers speed. For example, for more fibrous cereals high tip speed should be selected (Niqki, I., Pers. comm.). On the other hand if we want to get coarser particles then we can decrease the velocity of hammers. Wear of hammers and screen affect particle size and energy consumption. As, wear increases, particle size and capacity decreases, and energy consumption increases. Another factors affecting the grinding result is the distance between hammers and screen. Thus, closer distance results in finer grinding. Usually the distance is set to mm. But if the diameter of mill is larger, the particles will be coarser. The diameter of screen holes has proportional relation with throughput rate and particles size. The air suction system is a vital part of the horizontal hammer mill. Speed of the air suction out of the mill is an important factor affecting grinding efficiency and the grinding result (Svihus 2009, HFE 305 course). Generally, high air suction will boost grinding speed promoting the flow of particles through the chamber and this can reduce the energy consumption of the hammer mill. In addition to that air suction will result in much uniform particle output (Niqki, I. Pers. comm.). This is because the finer particles will be sucked and separated from normal particles. Air suction can also be important to prevent increase of temperature inside the grinding chamber. Feeding the hammer, is one of the most important factors affecting grinding efficiency. Even if the hammer mill is well-matched to its tasks and wellmaintained, it can cause problems, especially if it is not properly fed (Gill, 2013). Therefore, we should be highly careful deciding upon the feeding device for the hammer mill. According to the feeding device expert Alles (2003), there are two criteria for the performance of feeding device. 1. The feeder must provide a uniform curtain of material to the hammer mill grinding chamber and 2. This curtain of material must be fed full width of across the hammer mill chamber (Kvanne and Phillips, 2003). Poor uniformity in the feeding of hammer mill 12

14 can cause stability problems, excessive wear, reduced capacity, greater particle size variability and heating. 2.4 Roller Mill Roller mills are not widely used as hammer mills in the feed industry. But they still can be convenient for particular grinding cases. From personal communication with Nikqi I., and Miladinovic D., at NMBU Centre of Feed Technology, I have learned about typical advantages of roller mills like energy efficiency, uniform grinding result, low noise of operation, and low dust generation. But higher maintenance cost, poor result on grinding fibrous cereals and mixed grains can be considered as disadvantages of roller mills. Roller mills work best with friable products that have uniform shape and size. They do not work well with mixed grains (dissimilar shape and size). Roller mills do not alter size of fiber materials (Koch, 2008). Figure 2. Roller mill with two pairs of rolls (Feed machinery 2017) Basic roller mill The main grinding principle in the roller mill is compression. The materials from the delivery (feeding) device passes between one up to three counter rotating pairs of rolls and are squeezed. The rolls can rotate with equal or unequal speed. When there is a difference between two rolls velocity, shear and attrition also contributes to size reduction (Nikqi I., Pers.comm.). In each pair of rolls one roll is anchored in a fixed position but the other one can be adjusted in different ways. 13

15 This design allows us to control the size of grinded particles. Thus, we can adjust space between two rolls and this will determine the particle size. We can also adjust grinding properties by adjusting speed of two rolls and choosing rolls with different corrugation patterns. 2.5 Effect of grinding method on broiler performance Hammer and roller mill grinding don t effect on broiler performance, when diets of similar geometric mean particle diameter are compared (Nir et al., 1990). Geometric mean diameter is an accurate descriptor of particle size distribution only when log particle size is normally distributed (Lucas, 2004) and as the hammer mill grinding produces a greater amount of fine particles (Reece et al., 1985), which may confound results. 3 The pelleting process Pelleting is the most prevalent heat treatment in the production of poultry feed. The objective of pelleting is to agglomerate smaller feed particles into larger particles as pellets, to enhance the economics of production by increasing the feed intake, and thus growth performance and feed efficiency. However, due to the heat, moisture and mechanical pressure, applied during conditioning and pelleting, some chemical and physical alterations occur that may have beneficial or detrimental effects on feed components, gastrointestinal development and subsequent bird performance (Abdollahi et al., 2012). Pelleting process is done due to gelatinization of starch as just one of the reasons, but only to a small extent, and thus may be of modest relevance in starch digestion. Pelleting process may also result in partial denaturation of proteins; a process which can potentially improve protein and to some extent starch digestibility, due to inactivation of proteinaceous enzyme inhibitors (Abdollahi et al., 2012). Cell wall breakage, as a result of the physical stress of pelleting, may also provide greater accessibility of nutrient contents, previously encapsulated within endosperm sub-aleurone, to digestive enzymes. In diets based on viscous cereals, nutrient availability may be negatively affected through increased digestibility. viscosity as a result of either an increase in soluble carbohydrate concentration or changes in the molecular weight of soluble fibers or both, due to pelleting (Abdollahi et al., 2012). Pelleting process also remains a potentially aggressive process on the stability of exogenous feed enzymes and vitamins, a major concern of feed manufacturers. Particle size-reducing property of the pelleting process may result in a suboptimal gizzard development and thus reduced nutrient 14

16 digestibility of diets for poultry. While physical pellet quality is a critical factor to optimize feed efficiency and growth response of broilers. The present review highlights the balance between nutrient availability and physical quality of pellets which is critical in determining the actual performance of broilers. Under the conventional pelleting process, good pellet quality is usually obtained at the expense of nutritional quality. (Abdollahi, et al., 2012) 3.1 Important advantages of pelleting: Increased feed intake - (e.g. broiler chickens), decreased waste uniform shape prevents the animal to eliminate large or fine particles from feed. Pellet-fed birds spend less time and energy in the ingestion of feed, and obtain more nutrients per every unit of expended energy than those fed with mash diets (Jones et al., 1995; Vilarino et al., 1996). Also increased nutrient density and digestibility is done through decreased particle size, improved palatability, decreased microbiological activity, pelleting increases the bulk density of mash allowing more efficient transportation, and less dust. There are several factors affecting pellet quality like feed formulations, feed conditioning and grinding, considered as vital. 3.2 Important features of the pelleting process Characteristics of feeds which are produced by pellet mill: High possibility to produce sinking feeds, cooking rate is about 50%, moisture content is about 16-17%, additives like pellet binder should be used about 2-3%, there are fines in last product (it is acceptable until 5%), there is a risk to see a bacterial contamination in last product etc.. Pellet durability may be improved by manipulation of diet formulation. Use of raw materials with good binding ability such as wheat, barley, and use of pellet binders will have an influence (Kenny, 2007). The particle size of grinded feed materials has great influence on pellet quality. The large particles can reduce pellet strength. However as the particle size is reduced to grist, the surface area is increased and this will promote the particles tightly adhere to each other. Two main factors in the pre-conditioner should be considered carefully before pelleting: steam quality and retention time. Steam quality determines the temperature and moisture profile inside the conditioner. Wet steam transfers heat less efficiently (lower enthalpy of evaporation), than saturated steam and can cause uneven moisture distribution in the mash, resulting in choking or slipping of the pellet die (Kenny 2007). As retention time in the conditioner increase, it also increases the degree of starch gelatinization and protein denaturation, which both have positive influence on pellet quality. 15

17 4 Chemical composition of pelleted material Chemical composition of pelleted material has a large impact on the quality of pellets, as a result changes of certain chemical substances that occur during pelleting process (Thomas et al. 1998). The intensity of these changes depends on the conditioning parameters (Moran, 1989) as well as of parameters of the pelleting (Van der Poel, 1994). Chemical ingredients can be classified in the following groups of: starch, proteins, sugars, fibers, fats, inorganics, and water (Thomas et al., 1998). Starch is the main ingredient in cereals, and it s vital for energy source in animal nutrition (Zimonja and Svihus, 2009). During the thermal treatment in the presence of water, gelatinization of starch takes place. This is a process that involves structural changes, due to which comes to the bonding performance of gelatinized starch properties (Svihus and Gullord, 2002), as improves pellet quality (Heffner and Pfosten, 1973). However, the mechanism in which starch contributes to the binding characteristics is not completely clarified. The presence of water is a prerequisite for the process of gelatinization. In contrast, the proportion of water and starch should be 0.3: 1 (Lund, 1984). Many authors have pointed out, that to complete the gelatinization of starch, ratio of water and the starch should be as high as 1.5: 1 (Wootton and Bamunuarachchi, 1979). This indicates that during the pelletizing, water is the limiting factor for the complete starch gelatinization, due to the humidity of pelleted material it generally ranges up to 17-18%. However, to be effective as a binder, it is sufficient that the starch is pre gelatinized on the surface of the particles (Thomas and Van der Poel, 1996). With gelatinization of starch, protein denaturation also represents one of the reaction that improves the quality of pellets (Maier et al., 1999). Namely, the proteins in the pelleting process, in the effect of heat and friction, in the presence of water, are passing through a process of partial denaturation. As a result, it comes to the fore their adhesive properties which positively affects the hardness and abrasion of pellets (Wood, 1987; Thomas et al., 1997). The presence of simple sugars (mono and disaccharides) increases power consumption, due to pellet presses greater friction in the channels of the matrix. However, sugars have favorable effect on the quality of pellets, because during the cooling it s coming up to their recrystallization and establishing connections solid-solid (Friedrich and Robohm, 1982; Thomas et al., 1998). Fibers (non-starch polysaccharides) can be divided into insoluble and the water-insoluble (Frohlich, 1990; Lo, 1990). This division can be helpful in terms of explaining the operation of the 16

18 pelleting process. Water soluble fibers (glucans, arabinoxylans and pectins) increase the viscosity of pelleted material. Higher viscosity material, acts as a filler and like that, get surrounded by larger particles and fills the pores. Resulting in obtaining firmer pellet, lesser degree abrasion (Thomas et al., 1998) and a higher hardness. As the porosity of the pellet is one of the main factors that determine the hardness (Rumpf, 1958; Ouchiyama and Tanaka, 1985). The fibers have a water-insoluble dual role. On the one hand, it contribute to better linking of the particles during the pelleting, mutual interlaced and wrapping (Rumpf, 1958). On the other hand, due to their strength and elasticity, possible problems as pressure drops, after the release of the pellets from the channel matrix. Then, due to the operation of elastic forces, it hinders the structure of pellets. The longer retention of material in channel matrix (thick matrix, reducing the flow), to a large extent, neutralize the effect of elastic forces and allows production of good pellet quality (Thomas et al., 1998). Adding the fat in pelleted mixture, reduces the strength and increases the degree of abrasion (Stark, 1994; Angulo et al., 1996; Briggs et al., 1999). Fats act as a lubricant between the particles and the wall of channel matrix, and between the particles themselves, resulting in less friction and thereby lower the pressure in the channel matrix. This leads to increased rubbing of the end product (Kaliyan and Morey, 2008). Fats also due to its hydrophobic nature, inhibit the binding properties of other components, i.e. starch, protein and fiber, due to their hydrophobic nature (Thomas et al., 1997). Cavalcanti (2004) found that increasing the fat content above 6.5%, in the mixture based on corn and soybeans, is adversely affecting the quality of pellets. On the other hand, the addition of fat decreases energy of pellet press, and increases capacity, also due to slippery effect (Walter, 1990). 5 The mechanism of digestion in poultry The digestive tract of poultry is significantly different from other digestive organs of monogastric animals. One of the peculiarities of the extension to the end of the esophagus is - the crop, where material is retained between 3 and 15 hours, which depends on the structure of feed (such as atomized particles, retention is shorter) and on how much the animal is hungry (at hungry animal feed goes immediately to the craw and fills out the stomach). In the craw feed gets moisture, soften and swell, starting welding operation of saliva enzymes (Jovanović et al., 2000; Đorđević et al., 2009). 17

19 Figure 3. The digestive system of chicken (Dummies 2016) Craw continues in the stomach, which consists of two components: the glandular stomach (proventriculus) and muscular stomach (gizzard). On the mucosal proventriculus, there are openings which through whom glands that secrete pepsinogen, hydrochloric acid and rheum. It keeps feed briefly, starting protein breakdown and separation of mineral substances from the complex compound. Muscular stomach is significantly higher than the gland, it supplies the powerful muscles and rheum membranes, and it s thick and cornified, with transverse folds. In it, thanks to the strong muscle contractions, occur a strongly efficient comminution of feed. In this way, gizzard replaces chewing apparatus, which birds are missing (Đorđević et al., 2009). From the gizzard, material (chyme) enters the duodenum where digestion continues under the action of the enzyme pancreatic and intestinal juice and gall. Pancreatic juice contains proteolytic, amilolytic and lipolytic enzymes that break down most of the nutrients in this section of the digestive tract. In the other parts of the small intestine, it completes the digestion of nutrients below enzymes of the intestinal juice, containing peptidase enzymes, amylase and maltase. Part chyme 18

20 enters to two appendix, where the material is decomposed affected with present microflora (Đorđević et al., 2009). 5.1 Anatomy and Function of gizzard (grub) Since the birds have no teeth, and disintegrating of feed particles is necessary, in these animals led to the development of specific organs, gizzard, adapted for grinding of feed (Svihus, 2011; Rodgers et al, 2012). The largest part of gizzard consists of two thick lateral muscles and two thin muscle, on the front and rear. With respect to the longitudinal axis of the gizzard, thick and thin muscles are asymmetrically deployed, and contractions result in fragmentation of material feed particles (Svihus, 2011). The cycle begins with grinding of thin muscle contraction, in the opening of the pylorus and strong peristaltic contraction of the duodenum. Pylorus is a small opening at the end, which functions as a gizzard sieve and does not allow the passage of too large particles to the duodenum. Simultaneously with the contraction of duodenum, there is a thick muscle contraction in the gizzard, causing the amount of material to be pushed out into the duodenum, but also drawn new amount into proventriculus. After relaxing, thick muscle contraction occurs in gizzard proventriculus and also suppression of material in gizzard. The entire cycle of described contractions, takes place four times in minute and it shredded material particles due to rubbing against the walls of gizzard and about each other, during the contraction of thick muscles, while thin muscles transport material according to the zones of grinding between two thick muscle contractions (Duke, 1992). Although proventriculus is a separate body which precedes the gizzard, it have small volume and it s causing a short residence time of material. Therefore, the bulk of decomposition of nutrients happens under the influence of pepsinogen and hydrochloric acid, which is secreted in proventriculus of gizzard. In gizzard, contractions of the material are being returned to proventriculus in additional secretion of digestive juices in the same material. Therefore, the gizzard proventriculus, may be considered as unique whole. Mean residence time of material in proventriculus and gizzard ranges from 30 min to 1 hour (Duke, 1992). Larger particles must be chopped to a certain critical size to be able to go through the pylorus and abandon the gizzard (Moore, 1999). According to a survey conducted by Ferrnado et al. (1987), the critical particle size is between 0.5 and 1.5 mm. Data from Hetland et al. (2002; 2003) and Amerah et al. (2008) indicate that most of the particles that enter the duodenum, is less than 0.1 mm. According to research of 19

21 Amerah et al. (2008; 2009b), with an increase in the share of large particles of mixture, it comes to a significant increase in volume of gizzard that can be more than double. Close up particles are selectively retained in the gizzard (Hetland et al., 2003) until the time of retention of small particles does not change with the change of the share of large particles (Svihus et al., 2002). Although this indicates that the retention time of particles of different sizes is unequal, and mean residence time significantly increases under such conditions. If the retention time of the standard commercial mixtures with small proportion of large particles is approximately one hour, mean residence time of the mixture with increased proportion of large particles can reach up to two hours (Svihus, 2011). For gizzard it s also considered that play an important role in regulating the amount of ingested feed, also it regulates the flow of feed from craw (Chaplin et al., 1992). In pig or human, stomach has a key role in regulation of feed intake and in poultry that role has gizzard, or system gizzard / proventriculus, from where it sends a signal of satiety (Svihus, 2011). Even when the signal satiety in modern broiler overpowers their large appetites, gizzard can, if it is well developed, to prevent overeating thanks to his limited volume, in combination with a limited passage of feed from the gizzard to the duodenum (Ka et al., 2009; Cline et al., 2010). Thus it prevents overeating, which is undesirable phenomenon in growing broilers. 5.2 Influence of the structure of the mixture on the development and functioning of gizzard (grub) It is known that digestive tract of birds quickly adapts to the changes in feed composition. Various studies of wild birds has shown, that due to the large variation in the composition of feed throughout the year, there is a change in the size of the small intestine and the cecum (Klasing, 1998). Gizzard particularly quickly responds to changes in the composition of feed, primarily to the changes in the structure of mixture (Farner, 1960). Under the structure, is meant on the particle size distribution of the mixture, and the form in which the feed is given to animals, either powdered or pelleted. The particles of the mixture, after grinding and mixing, are usually merged into the pellets in order to increase feed intake, as well as to improve the technical characteristics of the mixture. That is the second level of the structure that can also be called a macrostructure. Already in the early parts of the digestive system, pellets are dissolved so that the macrostructure has no influence on the 20

22 development of the gizzard. Or to have any other effect except for increasing the amount of ingested feed (Svihus, 2011). On the other hand, it leads to a finer pelleting of microstructure and of mixture, due to fragmentation of particles that occurs during the pelleting process, which is particularly pronounced in the pelleting of mixtures with a high proportion of large particles (Engberg et al., 2002; Svihus et al., 2004b). Increasing the share of large particles in the mixture comes along with rapid and highly pronounced increasing of gizzard. Thus, the Biggs and Parsons (2009) found expressed zoom of gizzard at 7 days of age, when the whole grains of wheat were included in the mixture for feeding one-day broiler. Increment is the logical consequence of a larger need for grinding the feed, whereby it comes to increment of gizzard muscle. According to data from various studies, zoom can be up to 100% (Svihus, 2011). It was also observed that, when the introduction of the structural components of the feed start, it leads to increased capacity of gizzard, or mass of materials that can fit into it. This increase is more noticeable in relation to the increase size of gizzard (Hetland et al., 2003). An important dilemma is to be solved, is whether gizzard, which is poorly developed due to a lack of structural components in feed, or it is condition that can lead to weaker production characteristics of poultry. Wild ancestors of domestic poultry species, had in feeding large quantities of structural components, such as seeds or fibrous materials (Klasing, 2005). It is therefore logical to conclude that the local poultry adapted to feed with a high content of structural components and that they are necessary for normal development and function of gizzard (Svihus, 2011). O'Dell et al. (1959) found that in the absence of structural components not only that gizzard is less developed, it is more frequently reported that it s the occurrence of inflammation proventriculus, which is inter alia characterized by excessive and its proventriculus a tendency toward cracking. Jones and Taylor (2001) found that in the inclusion of integrated cereal nutrition, rarely comes to the appearance of zoomed proventriculus. All this indicates that the normal development of functional units, proventriculus / gizzard, it is necessary presence of structural components in a meal (Svihus, 2011). 5.3 Effect of particle size on digestive tract development and physiology The development of digestive tract of poultry, especially the gizzard, is known to be influenced by feed particle size, which is evident in chickens at 7 days of age. Nir et al. (1994) reported greater gizzard development and lower gizzard ph in 7-day old chicks fed with medium or coarser particle size diets, compared with those fine particulate diets. The gizzard is a muscular organ that reduces 21

23 the particle size of ingested feeds and mixes them with digestive enzymes (Duke, 1986). The mechanical pressure applied in grinding by the gizzard may exceed 585 kg/cm2 (Cabrera, 1994). When such grinding is carried out in feed mills, this has negative effects on gizzard size and gut function. As a result, the gizzard is relatively underdeveloped and the proventriculus becomes enlarged when broilers are fed with finely grinded, processed diets (Taylor and Jones, 2004). Under these conditions, the gizzard functions as a transit, rather than a grinding organ (Cummings, 1994). The relative weights of both the gizzard (Nir et al., 1995; Engberg et al., 2002) and the small intestine (Nir et al., 1995) have been shown to decrease when birds are fed with pelleted rather than mash diets. Feed particle size is positively related to the relative gizzard weight (Nir and Ptichi, 2001) when diets are made as mash. In pelleted diets, however, this is likely to depend on the particle size distribution after dissolution in the craw. Svihus et al. (2004a) found no effect of particle size prepelleting on gizzard weight when it was a hard wheat (hardness index 64), with geometric mean diameter varying between 600 and 1700 µm, was used. The explanation for this finding probably lies in the lack of differences in particle size distribution after pelleting in this study. In contrast, Peron et al.(2005) found that particle size differences remained even after pelleting in wheat-based diets, made from a hard wheat (hardness value, 83), with geometric mean diameter values of 380 and 955 µm, and that pelleted diets made from coarse particles significantly increased gizzard weights, compared to those made from fine wheat. This was probably due to resistance of the hard particulate material to reduction by the pelleting process. A large, well-developed gizzard improves gut motility (Ferket, 2000) through increasing the levels of cholecystokinin release (Svihus et al., 2004b), which stimulates the secretion of pancreatic enzymes and the gastro-duodenal refluxes (Duke, 1992; Li and Owyang, 1993). Coarse particles may slow the passage rate of digestion through the gizzard (Nir et al., 1994), increasing the exposure time of nutrients to digestive enzymes, which in turn, may improve energy utilization and nutrient digestibility (Carre, 2000). It has been reported that a lower ph of gizzard contents may increase pepsin activity (Gabriel et al., 2003) and improve protein digestion. It has also been suggested that lower ph of gizzard contents may reduce the risk of coccidiosis (Cumming, 1994) and feed-borne pathogens (Engberg et al., 2002). 22

24 Feed particle size has influence on the development of other segments of digestive tract in birds fed with mash diets. Nir et al. (1994) reported the hypertrophy of the small intestine and lowering of intestinal ph when they were fed with fine mash diets. Similar results were reported by Nir et al. (1995), who found lower relative duodenal weights in birds fed with coarse particle diets compared to those fed with fine particle diets. Interestingly, a similar pattern has also been recorded in the birds fed with whole-wheat diets (Gabriel et al., 2003). The significance of lower duodenal weights associated with coarse feed particles is unclear. 5.4 The optimal structure of feed for poultry The possibilities of modern types of poultry to break down structural components of feed are not tested to a greater extent, the question of the optimal structure of a mixture, or the optimal share of larger particles, there is no single answer. Hetland et al. (2002) found that adding 30% of uncomminuted wheat leads to increasing the share of larger particles that enter the duodenum. Adding 44% of wheat grain resulted in a significant reduction in the share of small particles of 0.04 mm in the duodenum, but at the same time there has been a decrease in feed efficiency. Smaller gains and poor utilization of nutrients were found in the appendix of 60% whole grain wheat. Similar reducing of weight gain was obtained in the experiment of Biggs and Parsons (2009), when the proportion of whole grain in a mixture of wheat is increased from 35 to 50%. From this we can conclude that there is no upper limit of share of large particles in the mixture, above which should go, in order not to disturb the growth rate and recoverable nutrients. Svihus et al. (2004b) examined the influence of particle size in mixture, on the size of gizzard in 10 different mixtures and it showed that there is a positive correlation between the content of particles larger than 1 mm and the development of gizzard, with the strongest correlation to the fraction of particles larger than 2.8 mm. The conclusion is that particles larger than 1 mm, confirm an encourage growth of gizzard and also confirms research of Nir et al. (1994), in which was an increase of the gizzard of 26%, when the only difference between the control and experimental mixtures was the fact that in the experimental was 25% more particle sizes of 1.18 to 1.70 mm. From this, it follows that the recommendations could be: at least 20% of particles larger than grains of 1.5 to 2.0 mm or at least 30% of particles larger than 1 mm (Svihus, 2011). In a study conducted by Nir and Ptichi (2001) was found that with the increase of broiler growth, the optimum value of GSP-a mixture is also increasing. Another issue regarding the structure of feed, is challenge that should it be used in powder form or pelleted form. The general view is that pelleted feed increases 23

25 the gain and leads to higher feed intake (Caleta, 1965; Choi et al., 1986; Nir et al., 1995). Genetic selection has led to the tremendous progress in gain of broilers, a pelleted feed can use genetic potential greater. However, as a result of accelerated growth, there was a disturbance in metabolism, bone development and in cardiovascular system (Trevidy, 2005). On the other hand, it has been shown that the use of powder feed increases the weight of the digestive system of broilers (Choi et al., 1986) and the length of the small intestine, jejunum and ileum (Nir et al., 1994), so as to take advantage of many nutrients rather. Also, it is preferable for gizzard to be greater developed, due to the presence of larger particles, which during the pelleting is mostly pulverized. However, there are many disadvantages of applying the powder mixture in breeding broilers (weight manipulation mixture, layering, choice of particles by animals, dusting, loss micro components, etc.). It can be concluded that the benefits of pelleting overcome the advantages of a larger share of large particles in pelleted diets, and the need to find a way to pelleted or granulated feed on a long way, without causing an excessive comminution of larger particles. 5.5 The effects of increasing the share of large particles in mixtures for poultry It has been found that the particle size of the material in the small intestine of poultry is less, if in the longer period of time benefits the mixtures with a higher proportion of large particles, compared to the use of mixtures of the same composition, but with a smaller proportion of large particles (Hetland et al., 2002, 2003; Amerah et al., 2009a). This is due to more developed gizzard and time efficient of grinded feed particles, in the use of a mixture of coarser granulation (Svihus, 2011). Usage of electron microscope, and Peron et.al. (2007) have noted ingredients, such as eg. starch granules, that are trapped in a coarse particles in the thin intestine. However, when the gizzard is well developed, the smaller will be the number of larger particles in the small intestine, and with that a better utilization of nutrients. Adding the structural components of the mixture for broilers leads to a reduction in ph value of gizzard content of 0.2 to 1.2 ph units. It can be explained by the higher volume of gizzard, and thus prolonged retention of feed, resulting in a greater amount of light and hydrochloric acid (Svihus, 2011). Since the ph value of feed is generally between 5.5 and 6.5, greater amounts of, will lead to an increase in the ph value in the gizzard. This is probably the main reason for the higher ph values that gizzard is using from pelleted feed, compared with the powder, since the 24

26 amount of incorporated pelleted feed is always higher (Engberg et al., 2002). The smaller share of large particles is due to pelleting, and grinding also contributes to this effect (Svihus et al. 2004b). The lower the ph value of the content of gizzard is, it contributes to improved digestion of feed, and in addition, also destruction of pathogenic microorganisms in nutrition. In this way, the functionality of gizzard indirectly influence on animal health (Svihus, 2011). Bacteria of the genus Salmonella is one of the leading causes of alimentary toxico infections of people and it is mostly associated with food products from poultry. The presence of larger particles over a longer period of time, leads to increased development of broilers and gizzard, its larger volume and capacity, resulting in more feed reserves, and pathogenic microorganisms are destroyed due to the low ph values (Huang et al., 2006). Similarly, the results of some studies also point up, to relieve symptoms of coccidiosis broilers with increasing the share of large particles of feed (Jacobs, 2011). Coccidiosis is a disease which is caused by protozoa of the genus Eimeria and it s a major problem in growing broilers. Followed by the reducing growth and weaker utilization of feed, causing a major economic loss (Braunius, 1987). Coccidiosis may be in the form of a slight infection, which have almost no negatively effect on the broiler, but they can also be manifested in the form of highly strong infections, causing high mortality (Williams, 1999). Increased incidence of this infection was, by introducing greater share of larger particles in the feed of broilers as a great potential, as this would avoid or greatly reduce the amount of applied coccidiostats, whose presence is prohibited in final products. As it was mentioned above, gizzard plays an important role in regulating the amount of feed intake and prevention overeating. Binge eating is characterized by normal weight gain, feed intake that is higher than the average, and the metabolic energy of less than 10.3 MJ / kg. Overeating and then poor utilization of feed ingredients, may lead to poorly development, due to small share of larger particles of the feed in gizzard (Svihus, 2011). Thus, the research of Peron et al. (2005) was that broilers were fed with a small portion of larger particles, causing the gizzard to be less developed. After the poultry are left to starve for a while, again they were given feed and there was a overeating, which resulted in reduced digestibility of starch. The study of Svihus et al. (2002), 4 out of 10 broilers were fed with finely-grinded wheat, showed signs of over eating. Adding the whole grains of wheat to broilers with symptoms of binge eating are eliminated. 25

27 Another positive effect of the presence of a greater proportion of larger particles is greater permeability of feed for the digestive juices in the stomach. The feed in the stomach is made up of a wide range of particle sizes, where in, the smaller particles fill the space between the larger. In this way, the finer particles reduce the permeability for digestive juices. Increased content leads to larger particles and appearance of the interspace, through which digestive juices goes, which results in a better digestion (Lentle et al., 2006). 5.6 Effect of particle size and particle size distribution on performance of poultry It must be recognized that not only the size of the feed particles, but also uniformity of particles size, is relevant in determining the influence of particle size on bird performance. Both particle size and shape may influence on the bird performance (Axe, 1995). Birds distinguish the differences in feed particle size by mechanoreceptors located in the beak (Gentle, 1979). Chickens are known to have a preference for larger feed particles (Schiffman, 1968), which is observed at all ages (Portella et al., 1988) and thoughts about particle size preference are changed with increased age were wright (Nir et al., 1994). This may be related to the size of the bird s gape (the width of the beak). Whilst beak width increases with age (Gentle, 1979), there are no published data relating to preferred particle size of gape. It is possible that the particle size must be increased with age for optimum of poultry performance. A more uniform diet will reduce the time spent searching for and selecting larger particles, with beneficial effects on performance. Using maizesoy diets in mash form, Nir et al., (1994) have shown that diets with lower geometric standard deviation gave higher weight gain and feed efficiency. Despite this importance, only limited studies have been carried out on the effects of particle size uniformity for different cereal grains in poultry feeds. This lack of interest may be due to the fact that the majority of the feed used in the production of broilers is fed with pelleted or crumbled feed, where there is no opportunity for selection of particles of different sizes (Reece et al., 1986). 26

28 6 Effect of particle size on pellet quality and feed production economy 6.1 Effect of particle size on pellet quality Good pellet quality is defined as the ability to withstand mechanical handling (bagging, transport etc) without breaking up, and to reach feeders without generating a high proportion of fines. Pellet quality is determined by two physical parameters, the pellet durability index (PDI) and pellet hardness. The PDI measures the proportion of fines generated during standardized mechanical handling (Behnke, 2001), typically in a tumbling can (ASAE, 1987) or Holman Pellet Tester (Holman Chemical Ltd, United Kingdom). Pellet hardness is determined, in a spring hardness tester, as the static force (in kg) is required to break the pellet. There is a positive correlation between pellet durability and feed efficiency (Carre et al., 2005). Higher pellet durability lowers the formation of fines and, reduces feed wastage and selection for larger particles by the birds. Pellet durability is thought to be inversely related to particle size (Angulo et al., 1996), based on the fact that smaller particles have more contact points with each other because of their larger surface area per unit volume (Behnke, 2001). Other factors affecting pellet durability include dietary protein and oil contents (Briggs et al., 1999), mash conditioning, die specifications, and cooling and drying (Behnke, 1996). Thus, any effect of particle size on pellet durability may be confounded by other dietary or milling parameters. High starch gelatinization has also been reported to improve pellet durability (Cramer et al., 2003). Therefore, it has been suggested that poor quality of the pellets associated with coarse particles is due to the low starch gelatinization in coarse particles compared to pellets made with fine particles (Svihus et al., 2004a). 6.2 Effect of particle size on energy cost in feed processing Feed constitutes, the greatest single cost in poultry production. The reduction of feed particle size is the second largest energy cost after the pelleting in the broiler industry (Reece et al., 1985) and likely to be the largest user of energy in the layer industry where pelleting is not performed (Deaton et al., 1989). Dozier (2002) estimated that the utility usage, comprised from 25 to 30% of the manufacturing cost is broiler feed. Reducing feed particles to a finer size requires greater energy use and lowers production rate. Thus, any reduction in energy consumption from grinding could significantly lower the feed cost. According to Reece et al. (1986) is reported that energy savings of 27% could be achieved by increasing the screen size of a hammer mill from 4.76 to 6.35 mm. However, the relationship between screen size and energy consumption is not linear. The energy 27

29 consumption during milling of maize with a hammer mill from a geometric mean diameter of 600 µm to one of 400 µm is double that required to reduce particle size from 1,000 to 600 µm (Wondra et al., 1995). Production rates are similarly non-linear (Wondra et al., 1995). Moreover, several studies have shown that fineness of grinding of grain has no effect on the rate/efficiency of pelleting (Martin, 1985) or power consumption during pelleting (Martin, 1985; Svihus et al., 2004a). Hence, any gain in productivity of birds from the reduction of particle size must be sufficient to offset the higher cost of fine grinding. 7 Discussion 7.1 Mash feed Mash quality is assessed by the size and uniformity of its particles. A positive correlation between the increase in feed particle size and broiler growth has been demonstrated by several authors, including Nir et al. (1994) on 0 to 3 week old chicks, and Leclercq et.al. (1998), on broilers between 22 to 39 days. Good uniformity of particle size is essential because birds prefer larger particles. Thus the dominant birds will quickly eat those larger cereal particles, while the rest of the birds will eat the finer particles. However, particle selection seems to be balanced by the birds since the cereal/concentrate consumption ratio in free choice eating is quite similar to that, for the whole feed (Trevidy, 2005) The improvement in performance with feed particle size and uniformity is explained by the lower energy output that birds make when they ingest larger particles. The number of pecks to eat the given one amount of feed, is reduced when particle size increases. Being grain eaters, bird have a digestive tract designed to quickly ingest large amounts of feed, that are stored in the craw to be hydrated and acidified by lactic acid secretion before going through the proventriculus (Trevidy, 2005). In the proventriculus, hydrochloric acid and pepsin and mucus secretions are increased when the feed particle size increases. The gizzard carries out feed grinding, feed impregnation and pre digestion of the feed by the secretions from the proventriculus, as well as the regulation of feed in-flow and out-flow. This will have an effect upon three digestive flow: from gizzard to proventriculus; from jejunum to duodenum; from rectum to 28

30 caeca. The intestinal peristatic motility slows down the feed flow, allows improved absorption of the nutrients by the intestinal viol, and helps to stabilize the intestinal flora (Trevidy, 2005). 7.2 Pelleted feed The effects of pelleting are well documented and they were mentioned above: higher feed density, no feed ingredient separation, better bacteriological quality, easier ingestion, improved growth and feed conversion ratio. However, these may vary according to the quality of the raw material, and from grinding and pelleting processes as well. The two main physical indicators of pellet quality are: hardness and durability. Broiler reaction to the above two quality criteria is not ease to assess. In many experiments where greater result were obtained with pelleted feed, precise mash characteristics were not given. Indeed, pellets always produce greater results when they are compared to the same fine mash as used to make a quality pellet, even more so when the energy level is low. This confirms that major effect of pelleting dwells in improvement of ingestion. However, a high energy feed presented either as a coarse mash containing whole grain or a medium quality pellet because of its fat content, will give greatly similar results in growth, FCR and fat deposit. 7.3 Effect of physical form of feed - mash versus pellets Interaction between particle size and feed physical form in broiler diets for weight gain and feed intake is well documented. Available data clearly suggest that grain particle size is more critical in mash feeds, than in pelleted or crumbled feeds (Reece et al., 1985, Cabrera, 1994; Nir et al., 1995; Svihus et al., 2004a; Peron et al., 2005). Pelleting is known to improve weight gain, feed intake and feed efficiency (Nir et al., 1995; Jensen, 2000; Nir and Ptichi, 2001). These improvements have been attributed inter alia to higher density, improved starch digestibility resulting from chemical changes during pelleting, increased nutrient intake, changes in physical form, and decreased energy spent for eating (Calet, 1965; Jensen, 2000). Similar improvements have been reported in laying hens (Morgan and Heywang, 1941). In contrast, Hamilton and Proudfoot (1995) reported that layers fed with mash diet performed better than those fed with crumbled diet. In recent years, the interest in feed particle size has increased, as the industry continues to search for ways of optimizing feed utilization and improving production efficiency. Recommendations 29

31 regarding optimum particle size, however, have been contradictory, as the results from feeding trials are confounded by a number of factors, including feed physical form, complexity of the diet, grain type, endosperm hardness, grinding method, pellet quality and particle size distribution. The extent of milling these seeds is known to influence a number of aspects of poultry production, including bird performance and digestive tract development. The aim of this comparison, is to review the published data on the influence of feed particle size on these aspects and, to highlight its implications for gut health and functionality. Data regarding the quantitative effects of degree of grinding on energy cost and pellet quality are also discussed. Nowadays, various commercial feed mills are producing different forms of broiler feed for different age group of bird. The physical form of feed (mash, pellet) is a crucial factor in meat yield of broiler. Feed constitutes about per cent of the total cost of broiler production (Banerjee, 1998). Different types of feed forms have been evolved in broiler production at the present time. Various feed forms i.e., pellet or mash that are to be supplied to broiler are the most important factors which directly influence the cost of mixed feed and production performance of broiler. The major objective of poultry feeding is the conversion of feedstuff into human food. The economic importance of poultry feeding, becomes apparent when it is realized that 60-70% of the total production cost of poultry is feed cost. For this reason, the efficient use of feed is extremely important in broiler production. Mash is a form of a complete feed that is finely grinded and mixed so that birds cannot easily separate out ingredients; each mouthful provides a wellbalanced diet. Simple manufacturing procedure is needed for mash form of feed. Mash diet gives greater unification of growth, less death loss and it s more economical. However, grinded feed is not so palatable and does not retain their nutritive value, so well as not grinded feed. Mendes et al. (1995) showed that birds fed with mash diets had a better feed conversion efficiency than those given the pellet. Proudfoot and Hulan (1982) observed that the incidence of sudden death syndrome (SDS) was significantly higher for broilers fed with crumble-pellet or grinded crumblepellet form diet, than for birds fed with mash. There were no significant differences in live weight gain between birds fed with mash diet and those given a complete pelleted diets (McAllister et al., 2000). Pellet system feeding is a modification of the mash system. It consists of mechanically pressing the mash into hard dry pellets or "artificial grains. Pellet is a form of complete feed that is compacted and extruded to about 1/8 inch in diameter and 1/4 inch long (Banerjee, 1998). The greatest advantage in using pellets is that there is little waste in feeding. 30

32 The disadvantage is that pellets are about 10 percent more expensive than the others which are not pelleted. Asha et al. (1998) reported that pellets had better-feed efficiency up to six-week age of birds. On the other hand Moran (1990) observed that pelleting of feed improves the body weight of poultry. Bolton and Blair (1977) reported that feed intake of broilers could be up to 10 per cent greater with crumble or pellets compared with mash. Feeding with each form of feed has its advantages and disadvantages. The effectiveness, digestibility and conversion efficiency of different forms of feed are also different. There were some studies that has been undertaken to compare the productive potential of broiler birds fed with pellet/mash feed. One of the studies have been done by (Amakiri et al., 2013), and the experiment was about one hundred and twenty (120) Marshal day old broiler chicks that were used in an experiment to compare the effects of pellet and mash feed on performance indices. The chicks were randomly assigned to two treatmeants consisting of 60 birds/treatment with 20 bird/ replicate in a feeding trial that lasted for 6 weeks. Result from growth studies revealed that there was no significant (P>0.05) difference between the pellets and mash. However, results obtained revealed that mash diet significantly (P<0.05) improved feed intake. The results on cost benefit ratio showed that the cost/kg feed in mash feed is cheaper than the pellets. It was concluded that mash diet had beneficial effects. Apart from creating a source of variety for the birds, and for easy handling, mash feeding is more profitable in terms of weight gain and feed intake. Mash feed is also cheaper and easily available unlike the pelleted feed. 7.4 Manufacturing cost energy consumption Energy is one of the most critical input resources in the manufacturing industries. In most of the cases, energy cost outweighs the costs of other resources such as raw material, labors, depreciation and maintenance (Fadare, 2003). Energy is one of the most important material bases for the economic growth and social development of a country or region. Scientific forecasts and analysis of energy consumption will be of great importance for the planning of energy strategies and policies. Nowadays, energy usage in agriculture has been intensified in response to continued growth of human population, tendency for an overall improved standard of living and limited supply of arable land; thus, the farmers use their inputs in excess and inefficiently, particularly when the inputs have low price or are available in plenty. The enhancement of energy efficiency 31

33 not only helps in improving competitiveness through cost reduction, also results in minimized energy-related environmental pollution, thus positively contributing towards sustainable development (Kizilaslan, 2009; Ghorbani et al., 2010) When grinding and pellleting is mentioned it s not possible to skip highly significant point, and that s economical point and cost of production. The purpose of the production is to get as lowest price of cost per unit, to decrease costs as much it is possible and that potential buyers get desired product in designed form for minimal prize. From all operations in feed mills, grinding and pelleting are operations which are taking 80% of energy requirements in process of making feed. Towards things that were said above, some examples and comparisons were done between some countries from different contintents. Table 2. Avarage power consumption in French feed mills (Trevidy, 2005) Electric consumption KWH/Ton Thermal consumption KWH/Ton Total consumption KWH/Ton Mash Average Minimum Maximum Pellets Avarage Minimum Maximum

34 In Table 2, it is obvius that energy consumption decreases when coarser grinding is done and vice versa, it is the same for pelleteing. Also it is obvious that pelleting process is the most demanding process in energy consumption, it s taking most of the power. Depending of raw materials and particle size energy consumption varies, and it will be shown in the table 3. Table 3. Energy consumption ratio dependent of different kind of raw materials (Trevidy, 2005) Raw material Consumption kwh/ton Raw Materials Consumption kwh/ton Wheat 15.0 Sunflower cake 8.0 Maize 9.0 Soya 5.5 Pea 11.5 Rapeseed cake 3.5 Power consumption and material loss increase with moisture: 1+% moisture=+ 10% more power In terms of power consumption as it was said, pelleting is the highest consuming operation. Pelleting quality is not easy to assess. Pellet binding must have good adhesion to reduce the production of fine particles during transportation, storage and distribution, yet they must not be too hard in order to avoid possible drops in consumption. Maize based feed pelleting is more difficult than that of wheat based feed. Several techiniques are used to improve pellet binding: finer grinding, the addition of high levels of steam, high temperature (80-85 degrees), possible use of an expander, the level of compression (the compresion rate of a dye is calculated by length/diameter=20). These techniques significanlty increase power consumption, but decision should be made upon do they provide quarantees of improved broiler perfomanced or not. Everything should be revised and to see is it profitable or no. 33

35 Figure 4. Costs for grinding and pelleting in French feed mills (Trevidy, 2005) Figure 4, shows everything what was mentioned above, and that s that with increasing of diameter of particles, costs are proportionally increasing in grinding and pelleting process, but when they were observed together, they were stable. In reality, comparing mash and pellet on the basis of the same feed formula is often a one sided exercise, as it should be finer to obtain a quality pellet. To compare pellet with a coarser mash, taking into account the addition grinding and pelleting cost, it is more relevant. There were some studies done in Egypt concerning energy consumption for poultry feed (pelleted or mash feed ). The determination of the energy consumption in manufacturing different type of feeds, rabbit, poultry it was their aim and large animal feeds (Dabbour et al., 2014) This was achieved by determining the energy consumed in each stage of processing to assess the most consumable stage in the different types of feed. but the focus will be on poultry and pelleted or mash feed. 34

36 90% 80% 70% 60% 50% 40% 30% 20% 10% 0% receiving grinding handling mixing cooling pelleting Figure 5. The percentage of energy consumption in manufacturing poultry feed pellets (Dabbour et al., 2014) As we can see, as it was mention above pelleting is obviusly taking part in most of the power consumption, concerning making pellets, the second one is grinding etc. 50% 45% 40% 35% 30% 25% 20% 15% 10% 5% 0% receiving grinding handling mixing Figure 6. percentage of energy consumption in manufacturing mash feed for poultry (Dabbour et al., 2014). 35

37 PC KWH/tonne Fig. 6, shows the percentage of energy consumption in manufacturing mash feed for poultry. Here is obviously different situation than on the Fig. 5, now the grinding has taken the one of highest parts in energy consumption, and it can vary dependent of screen size of hammer mill. Some of debate in the world of agriculture is also how to decrease power consumption in feed mills and certain operations. There are ways for sure, not known to everyone but different researches has been done, so one of the research was done in Norway in feed technology center in As called Fortek. Miladinovic and Salas (2014), did experiment how adding of different enzymes is affecting on power consumption in pelleting and grinding process and also on its pshycal quality, but main focus is on power consumption in pelleting and grinding process without adding any enzymes and water. It was consisted from 2 experiments, and first one was with ring die pelleting, and second one with different mixtures grinded in hammer mill with screen size 3 and 5mm. Experiment , ,5 4,8 5,1 5, t1 t2 t3 t4 t5 t6 t7 t8 Figure 7. Power consumption (PC, mean±s.e.m.) during pelleting with or withouts enzymes (Miladinovic and Salas, 2014). 36

38 For this thesis research, treatment number (T1) is important because there was no addition of enzymes, it is clearly visible that power consumption (PC) has the highest level in T1 and on the other hand in all other treatments treated with enzymes PC has decreased. So from PC view and aspiration on sustainable production and deacreasing the costs, it would be wise to use enzymes for pelleted feed. The situation is same with grinding, other part of their experiment was to see how will 6 different mixtures react with or without adding water and enzymes and it was used hammer mill with screen of 3mm and 5mm. Experiment 2 Figure 8. Power consumption (PC) for six different mixtures milled with 3 and 5 mm screen in a hammer mill (HM). Different letters indicate significant differences (Miladinovic and Salas 2014) Clearly, mix 1 without adding any water and enzymes had higher PC in grinding of 100% barley on screen size 3mm, and obviously with 5mm lower. On the other hand, all other mixtures are showing that with adding of enzymes and water it is possible to deacrese PC which is important, independent of which screen size during grinding is used. 37