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J APPL POULT RES 2006. 15:245-255
© 2006 Poultry Science Association
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Research Reports

Effect of Corn Particle Size and Pellet Texture on Broiler Performance in the Growing Phase

A. S. Parsons, N. P. Buchanan, K. P. Blemings, M. E. Wilson and J. S. Moritz1

Division of Animal and Veterinary Sciences, West Virginia University, Morgantown 26506

Correspondence: 1 Corresponding author: jsmoritz{at}mail.wvu.edu


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
A review of past literature revealed inconsistencies in recommended grain particle size for optimal broiler performance. Changing diet formulation and subsequent processing variables may alter pellet texture and potentially affect broiler performance. In the current study, ground corn, varying in size (781, 950, 1,042, 1,109, and 2,242 µm), was added to a soybean-based premix to create 5 different mash diets. Water and a commercial pellet binder were added separately to corn-soybean-based diets before steam pelleting to create 2 pelleted diets differing in texture (soft and hard, respectively). The objective was to evaluate corn particle size, pellet texture, and feed form variation of compound diets on 3- to 6-wk broiler performance, nutrient retention, carcass characteristics, TMEn, feed passage time, and particle size preference. Soft and hard pellets had similar pellet durability (90.4 and 86.2%, respectively) and fines (44.5 and 40.3%, respectively). Increasing particle size of mash diets improved nutrient retention. However, broiler performance and energy metabolism were decreased when corn particle size exceeded 1,042 µm. This observation was due, in part, to increased size and maintenance requirement of the gastrointestinal tract. Broilers fed hard pellets (1,856 g of pellet breaking force) had improved nutrient retention, TMEn, and subsequent performance compared with broilers fed soft pellets (1,662 g of pellet breaking force). Pellet texture may affect broilers in a manner similar to particle size.

Key Words: particle size • pellet texture • feed form • particle size preference


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Preparing grain by grinding before incorporating it into a compound diet improves broiler performance [1, 2]. However, studies focusing on optimal grain size, specifically corn particle size, have presented conflicting results. Smaller corn particle size has a greater surface area to volume ratio, increasing exposure to digestive enzymes and presumably decreasing energy needed for mastication [3]. Reece et al. [2] and Lott et al. [1] reported improved broiler performance when corn particle size decreased from 1,289 to 987 µm and from 1,173 to 710 µm, respectively. Further decreases (900 to 300 µm) have also resulted in improved performance [4]. In contrast, Nir [5] has shown that increasing corn particle size from 525 to 897 µm increased broiler performance. Feeding large-particle corn may produce beneficial effects similar to reports of whole grain feeding. Whole grain feeding has been associated with increased gut development and health; that is, a more muscular gizzard and less occurrence of proventricular dilatation [6]. Greater development of the broiler gastrointestinal tract suggests that feed may be retained in the upper digestive tract for a longer period allowing for increased enzymatic digestion [6, 7]. Concerning feed manufacture, improved pellet quality has been associated with a smaller grain particle size [8, 9]; however, reducing grain particle size has been shown to increase hammer mill energy consumption and decrease production rate [4, 8]. A comprehensive study exploring large corn particle size does not exist.

Nearly 80% of all US poultry feed is pelleted [10]. Broiler performance benefits associated with pelleting have been well documented [11, 12, 13, 14]. However, benefits are only realized if pellet integrity is maintained to consumption. Zatari et al. [15] showed that pellets of poor quality, simulated by a 25:75 pellet to fines ratio, diminished predicted performance improvements associated with pelleting. Moritz and coauthors [16, 17, 18] determined that incorporating water into feed formulations increased pellet durability, decreased fines, and improved broiler performance when compared with feeding pellets of lower moisture. The authors observed that these high-moisture pellets had a softer texture compared with more conventionally produced pellets. The effects of pellet texture on broiler performance have not been documented.

An understanding of grain particle size and pellet texture is critical for development of feed manufacture strategies that optimize broiler performance. The objectives of the current study were 1) to evaluate the effects of corn particle size, feed form, and pellet texture on broiler performance and carcass characteristics, and 2) to attempt to understand these effects in relation to TMEn, nutrient retention, feed passage time, and particle size preference.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Feed Manufacture and Formulation
Starter and grower mash feeds were manufactured at the West Virginia University pilot feed mill. All diets (Table 1Go) were corn-soybean-based and were formulated to meet or exceed 1994 NRC recommendations [19]. Corn was ground to an average 1,042-µm particle size for the starter feed utilizing a hammer mill with a 1/4-in. (6.35 mm) screen. Five mash grower diets were manufactured, differing only in corn particle size. The mean geometric particle size and log normal geometric standard deviation were calculated. Varying corn particle sizes, categorized as fine (781 ± 2.09 µm), small (950 ± 2.08 µm), medium (1,042 ± 2.13 µm), and large (1,109 ± 2.22 µm) were manufactured using hammer mill screens of 1/8 in. (3.18 mm), 3/16 in. (4.76 mm), 1/4 in. (6.35 mm), and 5/16 in. (7.94 mm), respectively. A coarse (2,242 ± 2.11 µm) corn particle size was created by hammer-milling corn without a screen. Particle size distribution is illustrated in Figure 1Go.


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  		Table 1. Ingredient percentages of diets formulated to NRC [19] specifications. All diets were adjusted in nutrient density for the percentage of added moisture or commercial pellet binder
 

Figure 1
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  		Figure 1. Corn particle size distribution (% of a 100-g corn sample) for fine, small, medium, large, and coarse corn.

 
Two additional grower diets were pelleted at a commercial feed mill using a 7800 series California pellet mill capable of manufacturing 50 ton (45.5 tonne) of feed/h. The corn used for pelleted diets had a particle size of 491 µm. Particle size was determined using a Ro-Tap particle size analyzer [20]. One pelleted diet, designated soft, contained added tap water at 2.5% of dietary inclusion and was manufactured at 5 to 7 ton/h (4.5 to 6.4 tonne/h) as observed in the feed mill control room. The diet formulation was adjusted to prevent nutrient dilution; for example, soybean oil inclusion was increased to prevent energy dilution. The other pelleted diet, designated hard, contained a commercial binder [21] at 0.2% dietary inclusion, and was manufactured at 5 to 6 ton/h (4.5 to 5.4 tonne/h). The source of corn and soybean meal was different for pelleted diets compared with mash.

Pelleted diets were transported 125 miles (201 km) to West Virginia University and tested for pellet durability using standard and modified procedures [22], fines [23], pellet breaking strength [24], bulk density [22], and water activity [25] (Table 2Go). All diets were analyzed for DM [26], CP, and CF [27] after 1 wk of storage (Table 1Go). Pellets were stored for 1 wk before DM analysis and water activity was performed to estimate bound moisture [16, 17, 18].


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  		Table 2. Pellet characteristics and processing variables1
 
Performance and Nutrient Retention
Two thousand, two hundred eight 1-d-old, straight-run 308 x 344 Ross broilers [40] were randomly allotted to 96 floor pens (0.69 x 2.44 m; 23 broilers per pen) located in a cross-ventilated negative pressure house. Pens contained fresh wood shavings, nipple drinkers, and feed pans adapted to hoppers for ad libitum access to water and feed.

Broilers were fed a starter mash pretest containing medium-sized corn for 3 wk. At the conclusion of the third week a representative sample of birds was killed by CO2 (asphyxiation), weighed, and analyzed for nitrogen [27] and lysine [28] to estimate the efficiency of lysine and nitrogen retention by comparative slaughter. The number of chicks per pen was reduced by removing any underdeveloped chicks as determined by visual inspection so that each pen contained 21 broilers (0.7 ft2/bird). Pen weight was then recorded. A pen was designated as an experimental unit. One bird from each pen was weighed and leg-banded for later determination of nitrogen and lysine retention. Lysine levels of mash and pelleted grower diets had analyzed values above 1.5 and 1.8%, respectively. The 7 grower diets were randomly assigned within each of 13 blocks consisting of 7 adjacent pens for a randomized complete block design. Lighting remained at 24 h for wk 1 to 4 and decreased 1 h for each remaining week. Temperature was regulated thermostatically by beginning chicks at 90°F (32.2°C) for the first week and decreasing the temperature by 5 °F (2.8°C) each remaining week.

Mortality was collected twice daily. Upon conclusion of the sixth week, feed consumption and pen live weight were recorded and live weight gain, feed efficiency, and percentage mortality were calculated for the wk 3 to 6 period. One male and 2 females were randomly selected from each pen, killed by CO2 (asphyxiation), and weighed. Boneless/skinless breast tissue, abdominal fat pad, gizzard (sliced open, rinsed, and blotted dry), and intestine (from bottom of gizzard to ileo-cecal junction and stripped of digesta) were weighed. Carcass characteristic weights were recorded relative to bird BW. Leg-banded birds were weighed, terminated by CO2 (asphyxiation), and gastrointestinal contents removed. These carcasses were frozen and ground. Subsamples were taken, quick-frozen in liquid nitrogen, and powdered. Carcass subsamples and feed were analyzed for nitrogen [27] and lysine content using reverse-phase HPLC after precolumn derivatization by phenylisothiocyanate as previously described [28]. Remaining birds were transported to a commercial processing facility.

TMEn
Forty-eight broilers (3 wk of age) initially brooded with birds from the performance study were randomly selected and transferred to a separate room utilizing cross ventilation and negative pressure. Each bird was placed in a 12 x 20 in (305 x 508 cm) raised wire cage containing nipple drinkers and an external feed trough for an adaptation period of 1 wk. An individually caged bird was designated as the experimental unit and blocks were comprised of 8 adjacent cages assigned by location in the room. The same 7 diets utilized in the performance study were randomly assigned to cages within each of 6 blocks. One cage in each block was not assigned a diet and was used to determine endogenous excreta energy. During the adaptation period all birds received ad libitum feed of assigned diets and water. At the conclusion of the adaptation period (fourth week), birds were restricted from feed for 24 h. Following restriction, feed was provided for 45 min, and then removed. Those birds not assigned a diet received no feed during this time. Total excreta were collected for 48 h from the time of feeding, air-dried, weighed, and ground. All samples were analyzed in duplicate for gross energy [29] and nitrogen [27]. Retained nitrogen was calculated and corrected for eventual uric acid formation and oxidation [30]. Nitrogen-corrected TME was calculated using the weight of feed consumed, total excreta, gross energy, and retained nitrogen oxidation values.

Feed Passage Time
One hundred forty-four, 1-d-old, straight-run 308 x 344 Ross broilers were allotted to floor pens (0.69 x 2.44 m) containing fresh wood shavings, nipple drinkers, and a feed pan adapted to a hopper for 0 to 3 wk. Each pen received a pretest mash starter diet (corn particle size of 870 µm) and water for ad libitum consumption. Upon conclusion of the 3-wk period, birds were transferred to a similar room as that utilized in the metabolism study and 3 birds per cage were placed in each of 48 raised wire cages for a 10-d adaptation period. Eight groups of 6 adjacently caged birds comprised blocks for a randomized complete block design. Six mash diets were manufactured utilizing similar formulation and corn particle size as those used in the performance study for each of the 5 mash diets (fine, small, medium, large, and coarse) and the soft pelleted diet. The soft pellet diet was tested to determine any effects of high soybean oil inclusion on feed passage time and was fed in mash form using the fine corn particle size to exclude feed-form effects. Each of the 6 diets was randomly assigned to cages within each block. Diets were fed to birds during the adaptation period and fecal samples were taken to determine percentage acid insoluble ash (AIA) from diets without added AIA. At the end of the adaptation period, birds were feed restricted for 24 h. Birds were fed 200 g/cage of the assigned experimental diets containing 0.5% AIA [31]. Feed was provided for a 2-h period, then removed and weighed to determine feed intake. A diet without added AIA corresponding to diets assigned to each cage was fed upon removal of diets containing added AIA. Fecal collection began 6 h after providing diets containing added AIA and continued every 2 h for the following 12 h, then at 24, 30, and 36 h post-AIA administration. Water was provided for ad libitum consumption throughout the experiment. Collected excreta were stored and analyzed for DM [26] and AIA [32]. Acid insoluble ash measurements were corrected for AIA contained in diets without added AIA.

Particle Size Preference
One hundred twenty 1-d-old, straight-run 308 x 344 Ross broilers were fed a starter mash pretest diet (1,042 µm) from 0 to 3 wk of age. Birds were then transferred to a room similar to that used in the TMEn study and placed in 40 raised wire cages (3 birds/cage) for a 10-d adaptation period. Each cage of 3 birds constituted an experimental unit. Eight groups of 5 adjacent cages provided blocks for a randomized complete block design. Upon conclusion of the adaptation period, birds (4.5 wk of age) were restricted from feed for 24 h. The 5 experimental mash diets that differed in particle size (Table 1Go) were randomly assigned to cages within each block. Experimental diets were supplied in 1.0-kg aliquots. Water was provided ad libitum. A 100-g feed sample was taken from each cage to determine initial diet particle size. Homogeneous feed samples (100 g) were taken following feed administration at 3-h intervals for a 12-h period. Homogeneity of feed samples was created by 30 s of manual stirring. Particle size analysis was performed on all test samples [20]. Preference was determined by comparing the average particle size at each time point with the initial average particle size of the assigned diet. Increases in diet particle size over time indicate a preference for smaller particles and vice versa.

All experimental protocols were approved by the West Virginia University Animal Care and Use Committee (ACUC # 02-1002).

Statistical Analysis
The GLM procedure of SAS [33] was used to determine effects of particle size and pellet texture on performance, carcass characteristics, TMEn, nutrient retention, feed passage time, and preference. Fisher’s least significant difference test was used for multiple comparisons between mean values. Linear and quadratic regression was performed with coefficients for unevenly spaced treatments to determine trends among mash diet variables. Nonsignificant quadratic terms were removed from the model. Trends in particle size preference were determined using a regression model with block and treatment as categorical values and time as a continuous variable. Contrasts were used to compare 3, 6, 9, or 12 h to time zero. In all analyses, {alpha} was 0.05.


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Particle Size
Broiler feed intake (FI) increased (P = 0.0001) and feed efficiency (FE) decreased (P = 0.0013) as dietary corn particle size increased (Table 3Go). Broilers fed diets containing coarse corn had significantly increased FI and decreased FE compared with birds fed most other mash diets. Hetland et al. [7] reported increased FI when feeding diets with high inclusions of whole cereals. The authors remarked that excessive feed wastage contributed to the increased FI. Excessive feed wastage was not observed in the current study. Past literature has also suggested that broilers may not be able to efficiently utilize large corn particles due to underdeveloped gastrointestinal tracts [1, 34]. In the current study, linear regression indicated that increased corn particle size significantly increased nitrogen retention. Similarly, increased corn particle size showed trends toward increased lysine retention (P = 0.0669). Hence, broilers fed larger particle corn did not seem to be affected by underdeveloped gastrointestinal tracts. Broilers fed coarse corn had significantly lower FE compared with broilers fed diets containing fine, small, or medium corn.


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  		Table 3. Influence of particle size and pellet texture on 3- to 6-wk broiler performance and nutrient retention (mean ± SD)
 
Breast weight and breast weight as a percentage of live weight decreased (P = 0.0149 and 0.0250, respectively) as dietary corn particle size increased (Table 4Go). Conversely, gizzard weight and gizzard weight as a percentage of live weight increased (P = 0.0123 and 0.0001, respectively). Fat pad weight per se was not significantly affected; however, fat pad weight as a percentage of live weight increased (P = 0.0289) as dietary corn particle size increased. Differences in fat pad weight as a percentage of live weight may have been confounded by larger changes in live weight, breast weight, and gizzard weight. Nir et al. [35] reported a positive relationship between gizzard weight and dietary particle size. Similarly, Healy [4] reported increased gizzard, proventriculus, and intestinal weights for chicks fed corn ground to 900 µm compared with that ground to 300 µm. In the current study, increased grain particle size seemed to increase the proportion of feed energy utilized for gizzard growth and maintenance as opposed to breast growth. This speculation is also supported by changes in feed efficiency (Table 3Go).


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  		Table 4. Influence of particle size and pellet texture on 6-wk broiler carcass characteristics (mean ± SD)
 
True metabolizable energy values were high relative to the calculated diet ME of 3,200 kcal/kg (Tables 1Go and 5Go). Values might have been high in general due to the fast-growing broiler model, timed feeding regimen, or high soybean oil inclusion of all diets. Increasing dietary corn particle size resulted in a quadratic effect on TMEn (P = 0.0042). Feeding diets containing medium corn particles resulted in the highest TMEn. Hetland et al. [7] reported that starch digestibility increased when broilers were fed whole wheat compared with ground wheat. The authors attributed increased starch digestibility to increased gizzard activity that would increase ingredient grinding and mixing. In the current study, the efficiency of nitrogen and lysine retention of broilers also suggested benefits of large particle feeding (Table 3Go).


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  		Table 5. Influence of particle size and pellet texture on 4.5-wk broiler TMEn (mean ± SD)
 
Feed passage time (FPT) data are illustrated at different collection times by the average percentage AIA of excreta in Table 6Go. Cage FI did not differ among diets (P = 0.4682). The maximum excretion of AIA for all diets occurred during the 6- and 8-h collection periods. Jensen et al. [13] reported maximum excretion of chromic oxide at similar times. Particle size did not significantly affect FPT. However, fine and small particle diets had numerically the highest AIA percentages at 6 h, suggesting increased FPT. Conversely, the coarse particle diet had numerically the lowest AIA percentage at 6, 8, and 10 h suggesting a decreased FPT. Nir et al. [35] reported that content weight of the gizzard was significantly less for diets containing small particles compared with large, suggesting a decreased particle retention time. Larger corn particles may have been retained in the gastrointestinal tract for an increased time that may contribute to increased nutrient digestion and energy metabolism.


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  		Table 6. Influence of particle size and fat inclusion level on passage time as determined by percentage of acid insoluble ash (AIA)
 
Consistent preference trends for feed particles among diets were not apparent (Table 7Go). However, any particle size preference from the initial diet particle size would indicate that birds are not consuming a homogeneous mix of ingredients and, therefore, a nutrient profile different from the calculated formulation. The medium- and large-particle diets illustrated no particle size preference (P > 0.05) for collection times of 3 and 6 h. The lack of particle preference may have contributed to increased performance. However, all mash diets illustrated a significant preference for larger particles for the 12-h collection period. Portella et al. [36] reported decreases in the concentration of larger particles in a crumbled diet over time.


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  		Table 7. Indication of preference determined by average particle size (µm) of diets as consumed over time
 
In summary, broilers obtained digestive benefits from consuming diets containing medium to coarse particle corn (i.e., 1,042 to 2,242 µm). In addition, broilers may consume a more balanced nutrient profile from medium and large particle corn (i.e., 1,042 and 1,109 µm) due to lack of particle size preference. However, feeding coarse corn (i.e., 2,242 µm) may increase gizzard growth and maintenance to an extent that compromises performance.

Pellet Texture
All physical characteristics of the pelleted diets were similar with the exception of texture as determined by breaking force (Table 2Go). Mean breaking force for pellets containing commercial binder was greater than that of pellets containing added water, 1,856.37 and 1,662.45 g respectively, producing a comparatively harder texture. The high percentages of fines for both diets are indicative of commercial pellet manufacture post cooling and transport [37].

Broilers fed hard pellets had significantly greater live weight gain and FE than those fed soft pellets (Table 3Go). Performance benefits of hard pellets compared with soft pellets may be derived by similar mechanisms as observed with increased corn particle size of mash diets. Nitrogen and lysine retention were significantly improved for broilers fed hard pellets compared with broilers fed soft pellets. In addition, Table 5Go illustrates that hard pellets produced a significant increase in TMEn compared with soft pellets. Carcass characteristics were not affected by pellet texture (P > 0.05; Table 4Go). Feed passage time was not performed on pelleted feed. However, the soft pellet formulation made with fine particle corn was assessed for feed passage time, due to its high soy oil inclusion (i.e., 6.3%). Feed passage time did not indicate significant treatment differences; however, the soft mash formulation illustrated numerically decreased feed passage time compared with the fine corn particle diet for 6- and 8-h collection periods (Table 6Go).

The current findings imply that a harder pellet texture may produce beneficial digestive and subsequent performance effects compared with pellets of softer texture. The hard pellet texture (1,856 g of breaking force) was not hard enough to produce carcass characteristic effects that were detrimental to performance but was able to produce favorable digestive effects despite being compared with the soft pelleted diet that had a higher inclusion of fat. Mateos et al. [38] suggest that supplemental fat may enhance the use of dietary energy by slowing the rate of passage of diets, creating an extracaloric effect. The precise mechanism of pellet texture effects on broiler performance remains unclear.


   CONCLUSIONS AND APPLICATIONS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
REFERENCES AND NOTES
 

  1. Feeding broilers medium to coarse particle corn (i.e., 1,042 to 2,242 µm) improved nutrient digestion; however, broilers fed coarse particle corn (i.e., 2,242 µm) demonstrated increased gizzard growth and perceived maintenance requirements that compromised performance. Digestive benefits of feeding medium to coarse particle corn may have resulted due to lack of particle preference during feeding and decreased feed passage time in the gastrointestinal tract.
  2. Broilers fed pellets of hard texture demonstrated improved nutrient retention and subsequent performance compared with broilers fed pellets of soft texture (1,856 and 1,662 g of pellet breaking force, respectively). Pellet texture may affect broilers in a manner similar to particle size.


   ACKNOWLEDGMENTS
 
This study was financed by Hatch funds allocated to West Virginia University, Project No. H-435 and USDA-NRI 2002-35208-11580. The authors acknowledge Fred Roe, Bill Miller, and Bill Jones for assistance with animal welfare. Mark Nazelrodt and Pilgrim’s Pride Corporation are appreciated for feed manufacture and broiler chick support.


   REFERENCES AND NOTES
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 

  1. Lott, B. D., E. J. Day, J. W. Deaton, and J. D. May. 1992. The effect of temperature, dietary energy level, and corn particle size on broiler performance. Poult. Sci. 71:618–624.[ISI][Medline]
  2. Reece, F. N., B. D. Lott, and J. W. Deaton. 1986. The effects of hammer mill screen size on ground corn particle size, pellet durability, and broiler performance. Poult. Sci. 65:1257–1261.
  3. Jurgens, M. H. 1993. Methods of feedstuff preparation. Pages 220–225 in Animal Feeding and Nutrition. 7th ed. Kendall/Hunt Publ. Co., Dubuque, IA.
  4. Healy, B. J. 1992. Nutritional value of selected sorghum grain for swine and poultry and effect of particle size on performance and intestinal morphology in young pigs and broiler chicks. M.S. Thesis. Kansas State Univ., Manhattan.
  5. Nir, I. 1994. Effect of particle size on performance. 1. Corn. Poult. Sci. 73:45–49.
  6. Jones, G. P. D., and R. D. Taylor. 2001. The incorporation of whole grain into pelleted broiler chicken diets: Production and physiological responses. Br. Poult. Sci. 42:477–483.[ISI][Medline]
  7. Hetland, H., B. Svihus, and V. Olaisen. 2002. Effect of feeding whole cereals on performance, starch digestibility and duodenal particle size distribution in broiler chickens. Br. Poult. Sci. 43:416–423.[ISI][Medline]
  8. Reece, F. N., B. D. Lott, and J. W. Deaton. 1986. Effects of environmental temperature and corn particle size on response of broilers to pelleted feed. Poult. Sci. 65:636–641.
  9. Wondra, K. J., J. D. Hancock, K. C. Behnke, R. H. Hines, and C. R. Stark. 1995. Effects of particle size and pelleting on growth performance, nutrient digestibility, and stomach morphology in finishing pigs. J. Anim. Sci. 73:757–763.[Abstract]
  10. Behnke, K. C. 1994. Factors affecting pellet quality. Pages 44–54 in Proc. Maryland Nutr. Conf. Feed Manuf., College Park, MD. Maryland Feed Ind. Counc. and Univ. Maryland, College Park.
  11. Runnels, T. D. 1976. The influence of feed texture on broiler performance. Poult. Sci. 55:1958–1961.
  12. Heywang, B. W., and R. B. Morgan. 1944. A comparison of a pelleted and unpelleted all-mash diet for growing chickens. Poult. Sci. 23:16–20.
  13. Jensen, L. S., L. H. Merill, C. V. Reddy, and J. McGinnis. 1962. Observations on eating patterns and rate of food passage of birds fed pelleted and unpelleted diets. Poult. Sci. 41:1414–1419.
  14. Nir, I., R. Hillel, I. Pitchi, and G. Shefet. 1995. Effect of particle size on performance. 3. Grinding pelleting interaction. Poult. Sci. 74:771–783.[ISI][Medline]
  15. Zatari, I. M., P. R. Ferket, and S. E. Scheideler. 1990. Effect of pellet integrity, calcium lignosulfonate, and dietary energy on the performance of summer-raised broiler chickens. Poult. Sci. 69(Suppl. 1):198. (Abstr.)
  16. Moritz, J. S., R. S. Beyer, K. J. Wilson, K. R. Cramer, L. J. McKinney, and F. J. Fairchild. 2001. Effect of moisture addition at the mixer to a corn-soybean-based diet on broiler performance. J. Appl. Poult. Res. 10:347–353.[Abstract/Free Full Text]
  17. Moritz, J. S., K. J. Wilson, K. R. Cramer, R. S. Beyer, L. J. McKinney, W. B. Cavalcanti, and X. Mo. 2002. Effect of formulation density, moisture and surfactant on feed manufacturing, pellet quality and broiler performance. J. Appl. Poult. Res. 11:155–163.[Abstract/Free Full Text]
  18. Moritz, J. S., K. R. Cramer, K. J. Wilson, and R. S. Beyer. 2003. Feed manufacture and feeding of rations with graded levels of added moisture formulated to different energy densities. J. Appl. Poult. Res. 12:371–381.[Abstract/Free Full Text]
  19. National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC.
  20. Ro-Tap particle size analyzer model RX-29 type 110V 60H2, WS Tyler, Mentor, OH. One hundred grams of ground corn for each diet was placed in a dust-tight enclosed series of stacked (No. 4, 6, ...) American Society for Testing and Materials (ASTM) screens affixed to the Ro-Tap particle size analyzer and shaken for 10 min. The screens were then separated and weighed. Particle size was calculated by subtracting the weight of the screen from the final weight of screen and sample after shaking. The mean geometric particle size and log normal geometric standard deviation were calculated as described by McEllhiney [39].
  21. Maxibond–urea-formaldehyde resin and calcium sulfate to aid in pelleting animal feed and included in the diet at 4 lb/ton.
  22. American Society of Agricultural Engineers. 1997. ASAE S269.4, Cubes, pellets, and crumbles-Definitions and methods for determining density, durability, and moisture. Standards 1997. Am. Soc. Agric. Eng., St. Joseph, MI. Due to the use of a 5/32 x 1.25 in. die, pellets were sifted in a No. 6 American Society for Testing and Materials (ASTM) screen. Five hundred grams of sifted pellets was placed in a dust-tight enclosure and tumbled for 10 min at 50 rpm. The enclosure was of the dimensions 5 x 12 x 12 in., with a 2 x 9 in. plate affixed diagonally along 1 of the 12 x 12 in. sides. The tumbled samples were then sifted again (No. 6 ASTM) and weighed. The pellet durability index was calculated by dividing the weight of pellets after tumbling by the weight of pellets before tumbling, then multiplying by 100. The modified pellet durability index was determined in a similar manner with the exception of adding 5, 13-mm hex nuts to the pretumbled sample to obtain added pellet pressure.
  23. American Society of Agricultural Engineers (ASAE). 1983. Methods of determining and expressing fineness of feed materials by sieving. Page 325 in: American Society of Agricultural Engineers Standard S 319. American Society of Agricultural Engineers Yearbook Standards ASAE, St. Joseph, MI.
  24. Pellet breaking strength was tested using a TA-HDi texture analyzer with a Warner-Bratzler blade.
  25. AOAC. 1990. Official Methods of Analysis. 16th ed. Association of Official Analytical Chemists, Arlington, VA. Water activity was analyzed using an AquaLab model CX2.
  26. American Association of Cereal Chemists. 1995. Moisture Air-Oven Method. AACC Method 44-15A. Approved Methods of the American Association of Analytical Chemists Vol II. St. Paul, MN.
  27. AOAC. 1990. Official Methods of Analysis. 15th ed. Association of Official Analytical Chemists, Arlington, VA.
  28. Stinefelt, B. M., J. C. Eya, K. J. Semmens, and K. P. Blemings. 2004. Effect of diet and strain on growth and performance in hybrid Bluegill. North Am. J. Aquac. 66:312–318.
  29. Isoperibol oxygen bomb calorimeter model 1266, Parr Instrument Company, Moline, IL.
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