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J APPL POULT RES 2008. 17:249-261. doi:10.3382/japr.2007-00081
© 2008 Poultry Science Association
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Research Reports

The Effect of Steam-Conditioning Practices on Pellet Quality and Growing Broiler Nutritional Value

S. E. Cutlip*, J. M. Hott*, N. P. Buchanan*, A. L. Rack*, J. D. Latshaw{dagger} and J. S. Moritz*,1

* Division of Animal and Nutritional Sciences, West Virginia University, Morgantown 26506; and {dagger} Department of Animal Sciences, The Ohio State University, Columbus 43210

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


   SUMMARY
TOP
 SUMMARY
DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Feed currently constitutes 60 to 65% of the total cost of broiler production. Pellets are the primary feed form for commercially reared broilers. Understanding how to optimize pellet quality through precision thermo-mechanical processing may impact broiler performance and nutrient availability, and thus cost of production. Steam conditioning represents a manipulable thermo-mechanical processing variable. Corn-soybean meal-based diets were conditioned with 1 of 4 steam pressure x temperature combinations: 138 kPa at 82.2°C, 138 kPa at 93.3°C, 552 kPa at 82.2°C, or 552 kPa at 93.3°C. High steam pressure and temperature conditioning were shown to increase pellet quality. Three additional diets were prepared: unprocessed mash, the 552 kPa/93.3°C diet reground to mash, and a 50:50 combination of pellets and mash produced from the 552 kPa/93.3°C treatment to simulate a high fine percentage diet. All diets were fed to Cobb 500 broilers from 21 to 38 d, and nutrient availability was determined with Single Comb White Leghorn roosters. Broilers fed pellets conditioned with high steam temperature demonstrated decreased feed intake and feed conversion ratio. Amino acid and energy availability were not affected by variations in steam conditioning.

Key Words: broiler performance • feed manufacturing • steam conditioning • pellet quality


   DESCRIPTION OF PROBLEM
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Universally accepted recommendations for pellet manufacture do not exist. Easily manipulated processing variables include steam pressure and conditioning temperature; the pressures and temperatures utilized for steam conditioning by feed manufacturers vary among mills. The most commonly used values for pressure range from 138 to 552 kPa, whereas conditioning temperature may fluctuate from 76.7 to 93.3°C. Past research has not accounted for these variables in a comprehensive manner. The proper combination of steam pressure and conditioning temperature may affect the nutritional value of a feedstuff and the structural integrity of the pellet being produced. Commercial practices, as well as past research, do not agree on one optimal setting for steam pressure or conditioning temperature.

Some studies demonstrate that the pressure at which a feed is pelleted has no influence on the quality of the pellet or effectiveness of the resultant feedstuff [1, 2]; however, other studies claim an optimal pressure value exists [3–5]. The 2 most studied steam pressures are 138 kPa (20 psig) and 552 kPa (80 psig); these are generally referred to as low and high pressures, respectively. MacBain [3] found that the use of 138 kPa (20 psig) steam pressure during conditioning created higher quality pellets than those processed at 552 kPa (80 psig). Conversely, Leaver [4] found that more durable pellets were created with 552 kPa (80 psig) steam pressure conditioning. Research also exists claiming no difference in pellet quality with either pressure [1, 2]. As recently as 1999, Briggs et al. [5] recommended using a pressure between the low and high values previously studied. The authors concluded that most systems cannot sufficiently remove condensate formed by low pressure conditioning, subsequently creating a wet choke at the die. Moreover, high pressure conditioning was described as energy inefficient [5].

Optimal conditioning temperature is also a debatable pelleting variable. Heat applied during conditioning may aid in the destruction of pathogens (i.e., Salmonella), and anti-nutritive factors found in certain ingredients (i.e., trypsin inhibitor in soybean meal). High temperatures are needed for proper agglomeration of nutrients and are essential for achieving high pellet quality [6]. However, a heat threshold may exist. If pelleting temperatures are too high, then nutrient availability may be compromised, particularly the availability of proteins. In fact, high starch rations have been suggested to be capable of steam conditioning at temperatures higher than diets high in protein or fiber [7]. Bayley and colleagues [8] found that growth performance decreased with a steam conditioning temperature of 90°C (194°F), whereas conditioning at 70°C (158°F) was shown to increase performance. In addition, the moisture content of feed was observed to increase after being conditioned with high temperature steam.

Additional research has claimed that moisture addition during pelleting may have negative effects, such as adding more weight per volume of feed, therefore increasing transportation cost [9]. Moritz and others [10] found that the addition of moisture at the mixer tended to enhance pellet durability and decrease pellet mill energy consumption as a result of the added lubrication at the die. Regardless of moisture addition outcomes, the ability to increase feed moisture through steam conditioning has dependence on ambient atmospheric conditions, as well as the nutrient composition of the diet. Our current understanding of the pellet processing variables, steam pressure, and conditioning temperature is inconclusive, thus requiring more research in the steam conditioning facet of feed manufacture. The following study aimed to provide a general recommendation for optimal pellet processing based on steam pressure and conditioning temperature extremes, replicated milling, Cobb 500 broiler [11] performance, and rooster digestible amino acids and metabolizable energy.


   MATERIALS AND METHODS
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
Experiment 1: Diet Preparation
The experimental design consisted of a conditioning temperature x steam pressure factorial, manufactured using a Latin square. Treatments were blocked by day of manufacture. All treatments within a day of manufacture were from the same corn-soybean meal based diet formulated to 1994 NRC [12] broiler grower recommendations (Table 1Go). A 998.19 kg (2,200 lb) basal diet was mixed for 20 min using a single screw vertical mixer [13] before being dividing into 136.12 kg (300 lb) allotments for manufacture. Soybean oil was incorporated at the mixer.


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  		Table 1. Diet formulations and nutrient parameters (%, as-is basis)
 
All pelleted treatments were first passed through a 1.3-m (4 ft) long conditioner with a diameter of 0.31 m (1 ft) [14]. The feeder screw rate was set to achieve a pellet production rate of slightly less than 0.91 MT/h (1 ton/h). The conditioner contained 21 picks divided into 3 sets of 7 that were set at 10°, parallel and 10° angles relative to the shaft, and was run at a constant speed of 429 rpm. Under these conditions, a retention time of approximately 10 s was maintained for all pelleted treatments. A dedicated Columbia 25 BHP boiler provided saturated steam to the mill [15]. As steam traveled from the boiler into the conditioner, it passed through a series of 4 steam traps to separate excess moisture from the steam. Steam pressure was controlled by a globe value, and further throttled into the conditioner by a ball valve; here steam was injected at 3 separate ports at the center of the conditioner. Once conditioned, mash was then extruded through a 4.76 mm (3/16 in.) x 44.96 mm (1 3/4 in) die using a 40 HP Pellet Mill [14]. The die thickness/length to die hole diameter ratio was 9.45 for all pelleted treatments. A 10:1 ratio has been suggested as optimal for high grain rations [14].

The pellets were cooled with ambient air utilizing a horizontal cooler [16]. Four variations of conditioning temperature and steam pressure variables were integrated into the 2 x 2 factorial design: 138 kPa (20 psig) at 82.2°C (180°F), 138 kPa (20 psig) at 93.3°C (200°F), 552 kPa (80 psig) at 82.2°C (180°F), or 552 kPa (80 psig) at 93.3°C (200°F). These diets herein are referred to as low pressure/low temperature (LPLT), low pressure/high temperature (LPHT), high pressure/low temperature (HPLT), and high pressure/high temperature (HPHT), respectively. The aforementioned treatments were selected because they are attainable variables in most commercial mills and past research exists for comparison. Three additional treatments were created: unprocessed mash, HPHT treatment reground to mash, and a 50:50 mixture of the HPHT pelleted diet and a re-ground version of the same treatment to simulate a high fine percentage diet. The HPHT treatment, having the highest pellet quality, was selected to create the reground treatment as well as the 50:50 to further extrapolate differences associated with feed form. Each treatment was replicated 4 times on 4 consecutive days to comply with the Latin square design. The 4 pelleted diets were analyzed for moisture, mineral, and protein content [17, 18]. Bulk density, pellet durability index (PDI), and modified pellet durability index (MPDI) were measured [19]. Fines were collected and measured from both underneath the horizontal cooler and from a sample of bagged pellets collected at the sack-off bin. These values were combined to obtain an estimation of total fines percentage. The mean ambient temperature and relative humidity during the 4 d of pelleting were 25°C (77°F) and 84.5%, respectively. All treatment feeds were stored in a 7.2°C (45°F) cool room for 2 wk before being fed to the broilers in experiment 2.

Experiment 2: Broiler Performance
Eight hundred ninety-six Cobb x Cobb 500 broilers [11] of mixed sex were fed 1 of the 7 dietary treatments from experiment 1 and evaluated based on performance and carcass quality. Broilers were housed in a negative pressure barn; lighting, temperature, and ventilation were monitored and altered to create optimal rearing conditions. Temperature was initially set at 32°C (90°F) and was decreased each week until the mean room temperature was 21°C (70°F). Throughout the grow-out period, the mean ambient temperature was 23°C (74°F) with an average relative humidity of 72%. Broilers were allotted 23 h of light from 0 to 7 d, 20 h of light from 8 to 14 d, 18 h of light from 15 to 28 d, and returned to 23 h from 29 to 39 d. Each pen contained nipple drinkers, feed pans attached to hoppers and fresh wood shavings. Each of the 7 treatments was fed to 8 replicate pens housing 16 randomly assigned chicks at a density of 0.09 m2 (1 ft2) per bird. Feed and water were provided for ad libitum consumption. The high fines percentage diet was simulated by alternating feeders of pellets and reground pellets every other day.

On d 21 and 39, each pen of broilers was weighed, and feed consumed was calculated. On d 39, bone-in fillets with tender and fat pads were extracted from 2 female broilers within 100 g ± the mean female weight per pen. Only broilers given 1 of the 4 pelleted diets were utilized for the carcass quality analysis.

Experiment 3: Rooster Digestible Amino Acids and Metabolizable Energy
Single Comb White Leghorn roosters (not cecectomized) were fed each diet to calculate true metabolizable energy corrected for zero nitrogen retention (TMEn) and true amino acid digestibility (TAAD). Roosters were fasted for 24 h before being precision fed approximately 25 g of each diet. Control birds were fed corn starch to obtain endogenous protein and energy loss. Twenty-four hours after roosters were precision fed, excreta were collected, weighed, and then dried at 55°C (131°F) for 48 h. Once dry, all excreta were ground with a mortar and pestle. Gross energy, amino acid, and nitrogen content were determined for each sample [20–22].

Statistical Analysis
Feed manufacture treatment structure consisted of a pressure x temperature factorial within a Latin square design. The experimental unit consisted of one 136-kg (300 lb) batch of feed. Pressure and temperature main effects as well as the pressure x temperature interaction were determined. Treatment means were further analyzed using Fisher’s least significant difference test.

Broiler performance and nutrient availability experiments were conducted as a randomized complete block design. The experimental unit consisted of a pen of 16 Cobb 500 broilers or an individually caged Single Comb White Leghorn rooster, respectively. Pressure and temperature main effects as well as the pressure x temperature interaction were determined. Treatment means were further analyzed using Fisher’s least significant difference test; however, these experiments compared all 7 diets. Additionally, linear and quadratic regression analyses were performed among the reground mash, 50/50 re-ground mash and pellets, and all pellets (552 kPa, 93.3°C). Nonsignificant quadratic terms were removed from the model. These analyses were performed to provide a very simple summary of trends in feed form variations produced by similar conditioning practice and were not intended to produce a model for prediction. The broiler performance experiment utilized male to female ratio as a covariate. All data were statistically analyzed using the GLM procedure of the Statistical Analysis System [23]. Alpha was designated as 0.05, and letter superscripts were used to denote differences among treatment means.


   RESULTS AND DISCUSSION
TOP
 SUMMARY
 DESCRIPTION OF PROBLEM
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS AND APPLICATIONS
 REFERENCES AND NOTES
 
The current study emphatically demonstrates the feeding benefits of pellets for broilers in the growing phase. On average, broilers fed pelleted diets increased ending body weight by 433 g and decreased feed conversion ratio by 10 points compared with broilers fed the same diet as unprocessed mash. More importantly, this study demonstrates that small improvements in pellet quality (i.e., a 4 percentage point improvement in the pellet durability index) may significantly improve broiler performance, resulting in a 20-point decrease in feed conversion ratio and maintaining similar broiler weight gain.

Feed Manufacture and Pellet Quality
Increasing conditioning temperature increased pellet mill production rate (P = 0.07), PDI (P = 0.0001), and MPDI (P = 0.0001) as well as decreased the percentage of total fines produced (P = 0.04, Table 2Go). These results were likely associated with increased moisture and heat that provided additional die lubrication and feed particle adhesion [10, 24, 25]. Although total fines were affected by variation in conditioning temperature, percentages of crude protein and ash among sifted pellets and sifted fines were not different (P ≥ 0.05; Table 3Go). However, sifted pellets from HT conditioning illustrated increased moisture levels compared with sifted pellets from LT conditioning (P = 0.005; Table 3Go). High temperature conditioning in the current study was possible due to high ambient temperature (25°C) and low ingredient, thus preprocessed mash moisture content (11%, Figure 1Go). These variables prevented a wet choke or the condition where high conditioned mash moisture levels inhibit the necessary friction between the rolls and conditioned mash that enable the extrusion of mash through the die, thus pellet formation. High temperature conditioning increased PDI and MPDI by 4.0 and 8.5 percentage points, respectively, and decreased total fines by 2.5 percentage points (Table 2Go).


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  		Table 2. Effect of steam conditioning feed on manufacturing variables and pellet quality (Latin square design—using day and processing order for blocking)
 

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  		Table 3. Effect of steam conditioning feed on moisture, protein, and ash content (Latin square design—using day and processing order for blocking)
 

Figure 1
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  		Figure 1. Significant temperature effect on feed moisture.

 
Increasing steam conditioning pressure increased PDI (P = 0.08) and MPDI (P = 0.03, Table 2Go). These results may be associated with increased enthalpy of high pressure steam [26]. High pressure conditioning increased PDI by 0.5 percentage points and MPDI by 1.5 percentage points. Pellet quality differences obtained with variations in steam pressure were not as dramatic as those associated with variations in conditioning temperature.

Pellet quality in the current study was high in all treatments compared with typical integrated broiler operations. This may be attributed to the use of a pellet die of suggested die thickness/length to die hole diameter ratio for high grain diets [14]. In addition, the rate at which feed was conveyed into the conditioner was maintained slightly below maximum capacity for the feed manufacturing system. However, it is important to note that pellets in this experiment did not undergo many of the attrition forces typical to those in an industry setting; therefore a PDI of 94% may not be practical.

Broiler Performance
Broiler weight at the start of the experiment (21 d) did not significantly differ among allotted treatment groups (P ≥ 0.05; Table 4Go). In general, broilers fed pelleted diets had increased feed intake and increased live weight gain compared with broilers fed mash diets (P ≤ 0.05). These results were likely associated with increased productive energy as described in past pelleting/feeding research [24, 27, 28]. Linear and quadratic regressions were performed among the reground mash, 50:50 reground mash and pellets, and all pellets (552 kPa, 93.3°C). This analysis was performed to assess trends in feed form variations produced by similar conditioning practice. Quadratic trends were not observed among these treatments (P ≥ 0.05). However, expected linear trends were observed. Feed intake, live weight gain, and ending body weight increased, whereas feed conversion decreased among birds fed mash, 50:50 reground mash, and pelleted treatments, respectively (P ≤ 0.05). When the unprocessed mash treatment was compared with the 50:50 reground mash and pellets treatment, differences were not apparent (P > 0.05). Perhaps the quality of the 50:50 reground mash and pellet treatment was too similar compared with the reground mash diet to elicit a broiler performance response. This observation suggests that high pellet quality may be necessary to fully obtain benefits of pelleting. In support, broilers fed the HPHT pellets had increased feed intake and live weight gain as well as decreased feed conversion ratio compared with broilers fed reground HPHT pellets (P ≤ 0.05).


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  		Table 4. Effect of steam conditioning and feed form on 21 to 39 d performance (randomized complete block design—using female to male ratio as a covariate)
 
Broilers fed HT pelleted diets demonstrated decreased feed intake (P = 0.06), similar live weight gain (P = 0.3) and decreased feed conversion ratio (P = 0.03) compared with broilers fed LT pelleted diets. These results are likely associated with increased PDI and MPDI, as well as decreased total fines of HT pellets. The HT pelleted diets had only a 4.0 percentage point improvement in PDI, compared with LT pelleted diets; however, feeding resulted in a 20-point decrease in feed conversion ratio. Past research has not shown such large performance benefits with a small improvement in PDI. Moritz and colleagues [10] found that feeding broilers diets differing by 25 percentage points in PDI (61.72 vs. 87.29) decreased feed conversion ratio by 5 points and maintained live weight gain. Additional research by Moritz and colleagues [24] demonstrated that feeding broilers diets differing by 4.0 percentage points in PDI (67.42 vs. 71.75) decreased feed conversion ratio by 2 points and maintained live weight gain. Perhaps feeding benefits of pellets are bettered with increasing pellet quality because the pellets in this study were of higher quality than those previously studied. In addition, high quality pellets may be of longer length than pellets of lesser quality. This observation has been documented in other experiments from our laboratory. In theory, broilers feeding on pellets of greater length would expend less energy in feed prehension compared with broilers feeding on shorter pellets. Pellet length is not sufficiently accounted for when pellet quality is defined by durability and fines percentage. Furthermore, broiler performance benefits were not seen between the HP and LP pelleted diets that differed in PDI by 0.5 percentage point.

Broiler performance appeared to be heavily influenced by feed form because benefits associated with pellets created by HPHT were lost when pellets were reground to mash or when pellet quality was simulated to be reduced. These results are similar to past research that demonstrated that regrinding pellets reduced feed consumption and gain to the level of mash diets [8].

Trends for improved breast yield were associated with broilers fed HP pellets compared with broilers fed LP pellets (P = 0.08; Table 5Go). Variations in conditioning temperature did not affect breast yield (P = 0.5). Fat pad percentage was not influenced by either steam conditioning variable (P ≥ 0.05). Pathogen content of feed before and after manufacture was not determined. Perhaps high temperature and pressure aided in the destruction of pathogens and contributed to improvements in performance and carcass characteristics [29]. However, this explanation was not consistently supported. In addition, all measured performance variables were similar between broilers fed unprocessed mash and broilers fed reground HPHT pellets (P ≥ 0.05, Table 4Go).


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  		Table 5. Effect of steam conditioning and feed form on 39-d breast and fat pad percentage (randomized complete block design—using female to male ratio as a covariate)
 
Nutrient Value
Nitrogen-corrected true ME did not differ among dietary treatments when tested with a Single Comb White Leghorn rooster model (Table 6Go). These results are congruent to past research demonstrating that metabolizable energy values did not differ between processed and unprocessed diets [30–32]. Additionally, TAAD did not differ among dietary treatments when tested with a Single Comb White Leghorn rooster model (Table 6Go). This result conflicts with research by Smith and Circle [33] who claim the availability of several amino acids is negatively affected by steam conditioning, specifically citing reduced lysine digestibility due to the Maillard reaction. This was not observed in the current study. However, consideration should be given to the current study’s use of 3% soybean oil addition at the mixer. Soybean oil has die-lubricating properties that may aid in maintaining energy and amino acid availability.


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  		Table 6. True amino acid digestibility and TMEn of dietary treatments fed to Single-Comb White Leghorn roosters
 
Potassium hydroxide (KOH) and urease assays were also completed on each treatment to determine the state of dietary protein after processing [34, 35]. The results did not differ among treatments, illustrating that the dietary protein was not over- or underprocessed. Perhaps the intact Single Comb White Leghorn rooster was not an adequate model to determine TAAD and TMEn for growing broilers. These roosters were not only mature animals, but differed in breed and productive purpose than the Cobb 500 used to obtain the performance results in the pelleting study. Therefore, metabolism between the 2 breeds may be variable. Additionally, intact roosters typically yield higher TAAD values [36].

Vitamins are susceptible to damage during thermo-mechanical processing. Vitamin A loss has been suggested to increase with pelleting due to high pressure created in the die [37]. According to NRC [12] vitamin A levels should be approximately 1500 IU/kg of feed for meat-type chickens; however, a factor of safety is typically applied. The maximum tolerance for vitamin A has been suggested to be 10 to 30 times higher than the required 1,500 IU/kg of feed [12]. For the current study, vitamin A in the form of retinyl acetate in a gelatin, lactose coat with antioxidant addition (BHT) was added to the basal diet at 7,200 IU/kg of feed, to accommodate losses sustained during pelleting. Two replicate samples of the pelleted diets were analyzed for vitamin A concentrations [38]. Results demonstrated slight oxidative damage occurred during processing. Feed manufacturing utilizing high steam conditioning pressure and temperature (552 kPa at 93.3°C) caused only a 6.7% loss in vitamin A relative to mash feed. However, vitamin A remained above recommended levels for all treatments, regardless of steam conditioning variation; these data are consistent with past research concerning pelleting temperature and coated/stabilized vitamin A retention [39].

In conclusion, the authors recommend using high steam conditioning variables when ambient atmospheric temperatures and ingredient characteristics permit. By thermo-mechanically processing diets using high steam conditioning temperature, feed manufacturers can increase production rate and create high quality pellets with the potential to improve broiler performance, without compromising the nutritional value of a corn-soybean meal based diet.


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

  1. High conditioning temperature (93.3°C or 200°F) increased moisture content, pellet mill production rate, and pellet quality.
  2. The resultant high quality pellets produced by high conditioning temperature (93.3°C or 200°F) decreased broiler feed intake and feed conversion ratio.
  3. A small improvement in pellet quality (i.e., 4.0 percentage point improvement in the pellet durability index) may significantly improve broiler performance (i.e., 20 point decrease in feed conversion ratio) while maintaining similar broiler weight gain.
  4. Varying conditioning temperature and pressure did not affect true amino acid digestibility or nitrogen-corrected true metabolizable energy as determined in roosters.
  5. As a general recommendation to feed mill manufacturers, the use of high temperature conditioning may improve the efficiency of thermo-mechanical processing, pellet quality, and broiler performance when ambient temperatures and ingredient moisture levels are compliant.


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

  1. Stevens, C. A. 1987. Starch gelatinization and the influence of particle size, steam pressure and die speed on the pelleting process. PhD Diss. Kansas State University, Manhattan.
  2. Thompson, E. C. 1968. Steam for the pellet mill. Feed and Farm Supply Dealer. Oct. pp. 26.
  3. MacBain, R. 1966. American Feed Manufacturers Association, Arlington, VA, pp. 1–28.
  4. Leaver, R. H. 1988. The pelleting process. Sprout-Bauer, Muncy, PA.
  5. Briggs, J. L., D. E. Maier, B. A. Watkins, and K. C. Behkne. 1999. Effects of ingredients and processing parameters on pellet quality. Poult. Sci. 78:1464–1471.[Abstract/Free Full Text]
  6. Thomas, M., and A. F. B. van der Poel. 1996. Physical quality of pelleted animal feed. 1. Criteria for pellet quality. Anim. Feed Sci. Technol. 61:89–112.[CrossRef]
  7. Maier, D. E., and J. Gardecki. 1993. Evaluation of pellet conditioning: Understanding steam. Feed Manage. 44:15.
  8. Bayley, H. S., J. D. Summers, and S. J. Slinger. 1968. The effect of steam pelleting feed ingredients on chick performance: Effect on phosphorous availability, metabolizable energy value and carcass composition. Poult. Sci. 47:1140–1148.[Web of Science][Medline]
  9. Dozier, W. A., III. 2001. Cost-effective pellet quality for meat birds. Feed Manage. 52:21–23.
  10. Moritz, J. S., R. S. Beyer, K. J. Wilson, and K. R. Cramer. 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]
  11. Cobb-Vantress Inc, Siloam Springs, AR.
  12. National Research Council. 1994. Nutrient Requirements of Poultry. 9th rev. ed. National Academy Press, Washington, DC.
  13. Avery Weigh-Tronix, Fairmont, MN.
  14. Master Model Pellet Mill, California Pellet Mill Company (CPM). Crawfordsville, IN.
  15. Columbia Boiler Company, Pottstown, PA.
  16. Pyramid Processing Equipment LLC, Stilwell, KS.
  17. Association of Official Analytical Chemists. 1990. Official Methods of Analysis (15th ed.) Association of Official Analytical Chemists, Arlington, VA. Dry matter determinations were completed by weighing two 0.5-g samples of each treatment into crucibles and drying them in an oven at 105°F for 16 h. Ash content was measured by first grinding each diet through a Wiley mill with a 1-mm screen. Approximately 0.5-g samples of each treatment were weighed out in aluminum pans and placed into an ashing oven overnight, cooled to room temperature, and then reweighed. The Kjeldahl method was used to determine crude protein: 0.5-g ground samples of each treatment were used for this analysis. Fat extractions were completed on the ground samples of each diet with petroleum ether in a Soxhlet apparatus. All samples analyzed were replicated for statistical purposes.
  18. American Association of Cereal Chemists. 1995. Moisture Air-Oven Method. AACC Method 44-15 A. Approved Methods of the American Association of Analytical Chemists Vol. II. St. Paul, MN.
  19. American Society for Agricultural Engineers, 1983. Methods for determining and expressing fineness of feed materials by sieving. Page 325 in American Society of Agricultural Engineers Standard S 319. Am. Soc. Agric. Eng. Yearbook Standards, Am. Soc. Am. Eng., St. Joseph, MI. Pellet durability index was determined by sifting 500 g of pellets from a treatment through a No. 6 American Society for Testing and Materials (ASTM) screen before being deposited into a Pfost tumbler. The sifted pellets were then tumbled in the container, dimensions 5 x 12 x 12 in., with a 2 x 9 in. plate fixed diagonally along the 12 x 12 in. side, for approximately 10 min at 50 rpm. The sample was then sifted again through the No. 6 (ASTM) mm screen, weighed, and the percentage of pellets was calculated by dividing the weight of pellets after tumbling by the weight of pellets before tumbling and then multiplying that value by 100. Modified pellet durability index was similarly measured, with the exception of the addition of five 13-mm hexagonal bolts to the 500 g of sample in the tumbler. Both analyses are meant to simulate the deleterious effects of transferring and handling the pellets.
  20. Isoperibol oxygen bomb calorimeter model 1266, Parr Instrument Co., Moline, IL.
  21. Experiment Station Chemical Laboratories, Agricultural Experiment Station, Univ. Missouri, Columbia.
  22. Kjeltec Auto 1030 analyzer, Foss Tecator, Eden Praire, MN.
  23. SAS Institute. 2000. The SAS System for Windows 2000. Release 8.1. SAS Institute Inc., Cary, NC.
  24. 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]
  25. Skoch, E. R., S. F. Binder, C. W. Deyoe, G. L. Allee, and K. C. Behnke. 1983. Effects of steam pelleting conditions and extrusion cooking on a swine diet containing wheat middlings. J. Anim. Sci. 57:929–935.[Abstract/Free Full Text]
  26. Woodruff, E. B., H. B. Lammers, and T. F. Lammers. 2005. Steam Plant Operation. 8th ed. McGraw-Hill Publishing Companies Inc., New York, NY.
  27. Reddy, C. V., L. S. Jensen, L. H. Merrill, and J. McGinnis. 1962. Influence of mechanical alteration of dietary density on energy available for chick growth. J. Nutr. 77:428–432.[Abstract/Free Full Text]
  28. Farrell, D. J. 1974. General principles and assumptions of calorimetry. Pages 1–24 in Energy Requirements for Poultry. T. R. Morris and B. M. Freeman, ed. Br. Poult. Sci., Ltd., Longman Groups Ltd., London, UK.
  29. Allred, J. B., R. E. Fry, L. S. Jensen, and J. McGinnis. 1957. Studies with chicks on the improvement in nutritive value of feed ingredients by pelleting. Poult. Sci. 36:1284–1289.[Web of Science]
  30. McIntosh, J. L., S. J. Slinger, I. R. Sibbald, and G. C. Ashton. 1962. Factors affecting the metabolizable energy content of poultry feeds. Poult. Sci. 41:445–456.[Web of Science]
  31. Bayley, H. S., S. J. Slinger, J. R. Aitken, J. Biely, D. R. Clandinin, J. B. O’Neil, A. R. Robblee, and J. L. Sell. 1968. The influence of method of crumbling diets containing different levels of protein and lysine on chick performance. Poult. Sci. 47:677–685.[Web of Science]
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J. M. Hott, N. P. Buchanan, S. E. Cutlip, and J. S. Moritz
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