Effect of Corn Particle Size and Pellet Texture on
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2006 Poultry Science Association, Inc. 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 Primary Audience: Nutritionists, Feed Manufacturers, Broiler Producers, Researchers SUMMARY 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 m), 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 m. 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 2006 J. Appl. Poult. Res. 15:245–255 DESCRIPTION OF PROBLEM m and from 1,173 to 710 m, respectively. Further decreases (900 to 300 m) have also Preparing grain by grinding before incorpo- resulted in improved performance . In contrast, rating it into a compound diet improves broiler performance [1, 2]. However, studies focusing on Nir  has shown that increasing corn particle optimal grain size, speciﬁcally corn particle size, size from 525 to 897 m increased broiler perfor- have presented conﬂicting results. Smaller corn mance. Feeding large-particle corn may produce particle size has a greater surface area to volume beneﬁcial effects similar to reports of whole grain ratio, increasing exposure to digestive enzymes feeding. Whole grain feeding has been associated and presumably decreasing energy needed for with increased gut development and health; that mastication . Reece et al.  and Lott et al. is, a more muscular gizzard and less occurrence of  reported improved broiler performance when proventricular dilatation . Greater development corn particle size decreased from 1,289 to 987 of the broiler gastrointestinal tract suggests that 1 Corresponding author: email@example.com 246 JAPR: Research Report Figure 1. Corn particle size distribution (% of a 100-g corn sample) for ﬁne, small, medium, large, and coarse corn. feed may be retained in the upper digestive tract Nearly 80% of all US poultry feed is pelleted for a longer period allowing for increased enzy- . Broiler performance beneﬁts associated with matic digestion [6, 7]. Concerning feed manufac- pelleting have been well documented [11, 12, 13, ture, improved pellet quality has been associated 14]. However, beneﬁts are only realized if pellet with a smaller grain particle size [8, 9]; however, integrity is maintained to consumption. Zatari et reducing grain particle size has been shown to al.  showed that pellets of poor quality, simu- increase hammer mill energy consumption and lated by a 25:75 pellet to ﬁnes ratio, diminished decrease production rate [4, 8]. A comprehensive predicted performance improvements associated study exploring large corn particle size does with pelleting. Moritz and coauthors [16, 17, 18] not exist. determined that incorporating water into feed for- PARSONS ET AL.: PARTICLE SIZE AND PERFORMANCE 247 Table 1. Ingredient percentages of diets formulated to NRC  speciﬁcations. All diets were adjusted in nutrient density for the percentage of added moisture or commercial pellet binder Grower Grower Grower Ingredient mash hard pellet soft pellet Yellow corn 62.813 62.405 59.286 Soybean meal (47.5%) 29.832 29.896 31.369 Soybean oil 4.395 4.540 6.314 Deﬂuorinated phosphate 1.578 1.579 1.631 Limestone 0.793 0.792 0.799 Poultry premix1 NB3000 0.250 0.250 0.250 Salt 0.138 0.138 0.142 Methionine 0.067 0.067 0.073 Coban 602 0.075 0.075 0.077 BMD 503 0.050 0.050 0.051 Thiamine premix 0.005 0.005 0.005 Vitamin D3 premix 0.003 0.003 0.003 Water — — 2.5 Maxibond4 — 0.200 — Calculated composition ME (kcal/kg) 3,200 3,200 3,200 CP (%) 19.875 19.871 20.326 CF (%) 7.036 7.165 8.818 Analyzed composition Fine Small Medium Large Coarse CP (%) 22.2 22.3 21.6 21.7 22.7 20.0 21.0 CF (%) 8.4 8.7 7.6 7.9 8.6 5.2 7.7 DM (%) 88.3 88.3 88.3 88.6 89.1 86.0 83.8 1 Supplied per kilogram of diet: manganese, 0.02%; zinc, 0.02%; iron, 0.01%; copper, 0.0025%; iodine, 0.0003%; selenium, 0.00003%; folic acid, 0.69 mg; choline, 386 mg; riboﬂavin, 6.61 mg; biotin, 0.03 mg; vitamin B6, 1.38 mg; niacin, 27.56 mg; pantothenic acid, 6.61 mg; thiamine, 2.20 mg; menadione, 0.83 mg; vitamin B12, 0.01 mg; vitamin E, 16.53 IU; vitamin D3, 2,133 ICU; vitamin A, 7,716 IU. 2 Active drug ingredient is monensin sodium, 60 g/lb (90 g/ton inclusion) as an aid in the prevention of coccidiosis caused by Eimeria necatrix, Eimeria tenella, Eimeria acervulina, Eimeria brunette, Eimeria mivati, and Eimeria maxima; Elanco Animal Health, Indianapolis, IN. 3 Bacitracin methylene disalicylate, 50 g/lb (50 g/ton inclusion) to increase weight gain and improve feed efﬁciency; Alpharma, Fort Lee, NJ. 4 Maxibond = urea-formalydehyde resin and calcium sulfate (4 lb/ton inclusion) as a pelleting aid used in animal feed; AG Research Inc., Joliet, IL. mulations increased pellet durability, decreased TMEn, nutrient retention, feed passage time, and ﬁnes, and improved broiler performance when particle size preference. compared with feeding pellets of lower moisture. The authors observed that these high-moisture MATERIALS AND METHODS pellets had a softer texture compared with more Feed Manufacture and Formulation conventionally produced pellets. The effects of pellet texture on broiler performance have not Starter and grower mash feeds were manufac- been documented. tured at the West Virginia University pilot feed An understanding of grain particle size and mill. All diets (Table 1) were corn-soybean-based pellet texture is critical for development of feed and were formulated to meet or exceed 1994 NRC manufacture strategies that optimize broiler per- recommendations . Corn was ground to an formance. The objectives of the current study average 1,042- m particle size for the starter feed were 1) to evaluate the effects of corn particle utilizing a hammer mill with a 1/4-in. (6.35 mm) size, feed form, and pellet texture on broiler per- screen. Five mash grower diets were manufac- formance and carcass characteristics, and 2) to tured, differing only in corn particle size. The attempt to understand these effects in relation to mean geometric particle size and log normal geo- 248 JAPR: Research Report Table 2. Pellet characteristics and processing variables1 Pellet type Variable Soft (water) Hard (binder) Corn particle size ( m) 491 491 Mean PDI2 (%) 90.4 86.2 Mean modiﬁed PDI3 (%) 82.8 80.4 Mean ﬁnes (%) 44.52 40.37 Mean breaking force4 (g) 1,662.45 1,856.4 Water activity5 0.672 0.653 Bulk density (lb/ft3) [kg/m3] 40.73 [650.28] 42.49 [678.45] P-rate6 (ton/h) [tonne/h] 5–7 [4.5–6.4] 5–6 [4.5–5.4] 1 Values are the average of triplicate determinations. 2 Pellet durability index . 3 Modiﬁed pellet durability index (utilizing 5, 13-mm hex nuts for added pressure on pellets). 4 Breaking force . 5 Water activity = ratio of vapor pressure generated by feed sample compared with that generated by pure water . 6 Production rate of the pellet mill. metric standard deviation were calculated. Vary- cedures , ﬁnes , pellet breaking strength ing corn particle sizes, categorized as ﬁne (781 , bulk density , and water activity  ± 2.09 m), small (950 ± 2.08 m), medium (Table 2). All diets were analyzed for DM , (1,042 ± 2.13 m), and large (1,109 ± 2.22 m) CP, and CF  after 1 wk of storage (Table 1). were manufactured using hammer mill screens Pellets were stored for 1 wk before DM analysis of 1/8 in. (3.18 mm), 3/16 in. (4.76 mm), 1/4 in. and water activity was performed to estimate (6.35 mm), and 5/16 in. (7.94 mm), respectively. bound moisture [16, 17, 18]. A coarse (2,242 ± 2.11 m) corn particle size was created by hammer-milling corn without a Performance and Nutrient Retention screen. Particle size distribution is illustrated in Two thousand, two hundred eight 1-d-old, Figure 1. straight-run 308 × 344 Ross broilers  were Two additional grower diets were pelleted randomly allotted to 96 ﬂoor pens (0.69 × 2.44 m; at a commercial feed mill using a 7800 series 23 broilers per pen) located in a cross-ventilated California pellet mill capable of manufacturing negative pressure house. Pens contained fresh 50 ton (45.5 tonne) of feed/h. The corn used wood shavings, nipple drinkers, and feed pans for pelleted diets had a particle size of 491 m. adapted to hoppers for ad libitum access to water Particle size was determined using a Ro-Tap parti- and feed. cle size analyzer . One pelleted diet, desig- Broilers were fed a starter mash pretest con- nated soft, contained added tap water at 2.5% of taining medium-sized corn for 3 wk. At the con- dietary inclusion and was manufactured at 5 to clusion of the third week a representative sample 7 ton/h (4.5 to 6.4 tonne/h) as observed in the of birds was killed by CO2 (asphyxiation), feed mill control room. The diet formulation was weighed, and analyzed for nitrogen  and ly- adjusted to prevent nutrient dilution; for example, sine  to estimate the efﬁciency of lysine and soybean oil inclusion was increased to prevent nitrogen retention by comparative slaughter. The energy dilution. The other pelleted diet, desig- number of chicks per pen was reduced by remov- nated hard, contained a commercial binder  ing any underdeveloped chicks as determined by at 0.2% dietary inclusion, and was manufactured visual inspection so that each pen contained 21 at 5 to 6 ton/h (4.5 to 5.4 tonne/h). The source broilers (0.7 ft2/bird). Pen weight was then re- of corn and soybean meal was different for pel- corded. A pen was designated as an experimental leted diets compared with mash. unit. One bird from each pen was weighed and Pelleted diets were transported 125 miles (201 leg-banded for later determination of nitrogen and km) to West Virginia University and tested for lysine retention. Lysine levels of mash and pel- pellet durability using standard and modiﬁed pro- leted grower diets had analyzed values above 1.5 PARSONS ET AL.: PARTICLE SIZE AND PERFORMANCE 249 Table 3. Inﬂuence of particle size and pellet texture on 3- to 6-wk broiler performance and nutrient retention (mean ± SD) Performance Nutrient retention2 Live weight Feed intake Feed efﬁciency1 Mortality ENR ELysR gain (kg) (pen) (kg) (kg/kg) (%) (%) (%) Mash treatments Fine corn mash 1.568 ± 0.11 63.004 ± 3.84b 0.520 ± 0.03a 0.732 ± 1.78 4.752 ± 0.79bc 2.619 ± 1.51 Small corn mash 1.590 ± 0.05 66.027 ± 3.63b 0.514 ± 0.02a 0 ± 0 4.294 ± 1.06c 2.227 ± 1.01 Medium corn mash 1.619 ± 0.06 65.602 ± 4.97b 0.517 ± 0.02a 0 ± 0 5.292 ± 0.69ab 3.896 ± 2.42 Large corn mash 1.566 ± 0.03 64.642 ± 4.32b 0.507 ± 0.02ab 0.771 ± 1.89 5.126 ± 0.50ab 3.475 ± 1.88 Coarse corn mash 1.610 ± 0.06 71.831 ± 8.66a 0.481 ± 0.06b 0.366 ± 1.32 5.725 ± 0.98a 3.896 ± 1.57 LSD3 value — 4.4185 0.0273 — 0.6082 — ANOVA 0.1362 0.0030 0.0444 0.2858 0.0003 0.0754 Pelleted treatments Soft pellet 1.604 ± 0.05b 66.075 ± 2.81 0.506 ± 0.02b 1.815 ± 3.08 4.501 ± 0.43b 2.587 ± 0.81b Hard pellet 1.711 ± 0.06a 67.785 ± 3.94 0.526 ± 0.02a 1.465 ± 3.00 5.367 ± 0.93a 4.785 ± 3.27a LSD value 0.0433 — 0.0175 — 0.5614 1.1894 ANOVA 0.0002 0.0793 0.0283 0.7853 0.0057 0.0331 P-values generated for linear regression of mash diets Linear regression 0.2415 0.0001 0.0013 0.9819 0.0009 0.0669 a–c Means within a column without a common superscript differ signiﬁcantly (P ≤ 0.05). 1 Feed efﬁciency was calculated using mortality weight. 2 ENR = efﬁciency of nitrogen retention: (g of nitrogen gained/g of nitrogen consumed) × 100; ElysR = efﬁciency of lysine retention = (g of Lys gained/g of Lys consumed) × 100. 3 Fisher’s least signiﬁcant difference value. and 1.8%, respectively. The 7 grower diets were dered. Carcass subsamples and feed were ana- randomly assigned within each of 13 blocks con- lyzed for nitrogen  and lysine content using sisting of 7 adjacent pens for a randomized com- reverse-phase HPLC after precolumn derivatiza- plete block design. Lighting remained at 24 h for tion by phenylisothiocyanate as previously de- wk 1 to 4 and decreased 1 h for each remaining scribed . Remaining birds were transported week. Temperature was regulated thermostati- to a commercial processing facility. cally by beginning chicks at 90°F (32.2°C) for the ﬁrst week and decreasing the temperature by TMEn 5°F (2.8°C) each remaining week. Forty-eight broilers (3 wk of age) initially Mortality was collected twice daily. Upon brooded with birds from the performance study conclusion of the sixth week, feed consumption were randomly selected and transferred to a sepa- and pen live weight were recorded and live weight rate room utilizing cross ventilation and negative gain, feed efﬁciency, and percentage mortality pressure. Each bird was placed in a 12 × 20 in were calculated for the wk 3 to 6 period. One (305 × 508 cm) raised wire cage containing nipple male and 2 females were randomly selected from drinkers and an external feed trough for an adapta- each pen, killed by CO2 (asphyxiation), and tion period of 1 wk. An individually caged bird weighed. Boneless/skinless breast tissue, abdomi- was designated as the experimental unit and nal fat pad, gizzard (sliced open, rinsed, and blot- blocks were comprised of 8 adjacent cages as- ted dry), and intestine (from bottom of gizzard to signed by location in the room. The same 7 diets ileo-cecal junction and stripped of digesta) were utilized in the performance study were randomly weighed. Carcass characteristic weights were re- assigned to cages within each of 6 blocks. One corded relative to bird BW. Leg-banded birds cage in each block was not assigned a diet and was were weighed, terminated by CO2 (asphyxiation), used to determine endogenous excreta energy. and gastrointestinal contents removed. These car- During the adaptation period all birds received casses were frozen and ground. Subsamples were ad libitum feed of assigned diets and water. At taken, quick-frozen in liquid nitrogen, and pow- the conclusion of the adaptation period (fourth 250 Table 4. Inﬂuence of particle size and pellet texture on 6-wk broiler carcass characteristics (mean ± SD) Carcass characteristics Breast Breast Gizzard Gizzard Fat pad Fat pad Intestine Intestine2 (kg) (%LW)1 (kg) (%LW) (kg) (%LW) (kg) (%LW) Mash treatments Fine corn mash 0.401 ± 0.05 17.34 ± 1.33 0.035 ± 0.01b 1.51 ± 0.25b 0.040 ± 0.01 1.74 ± 0.47 0.057 ± 0.01 2.49 ± 0.31 Small corn mash 0.420 ± 0.07 17.17 ± 1.49 0.038 ± 0.01ab 1.54 ± 0.17b 0.042 ± 0.01 1.74 ± 0.50 0.059 ± 0.01 2.41 ± 0.34 Medium corn mash 0.383 ± 0.09 17.00 ± 2.30 0.036 ± 0.01b 1.60 ± 0.24b 0.040 ± 0.01 1.77 ± 0.35 0.056 ± 0.01 2.50 ± 0.43 Large corn mash 0.390 ± 0.07 17.29 ± 1.80 0.036 ± 0.01b 1.61 ± 0.28b 0.041 ± 0.01 1.86 ± 0.61 0.055 ± 0.01 2.42 ± 0.27 Coarse corn mash 0.362 ± 0.06 15.97 ± 1.80 0.041 ± 0.01a 1.81 ± 0.22a 0.046 ± 0.01 2.03 ± 0.48 0.057 ± 0.01 2.54 ± 0.29 LSD3 value — — 0.0054 0.1358 — — — — ANOVA 0.0579 0.0535 0.0107 0.0002 0.3750 0.2221 0.7292 0.6322 Pelleted treatments Soft pellet 0.410 ± 0.06 17.95 ± 1.23 0.027 ± 0.01 1.20 ± 0.18 0.038 ± 0.01 1.66 ± 0.33 0.057 ± 0.01 2.51 ± 0.37 Hard pellet 0.410 ± 0.07 17.34 ± 2.06 0.029 ± 0.01 1.28 ± 0.24 0.042 ± 0.02 1.84 ± 0.86 0.063 ± 0.01 2.66 ± 0.34 LSD value — — — — — — — — ANOVA 0.9129 0.2283 0.0666 0.2079 0.2381 0.3520 0.1034 0.1900 P-values generated for linear regression of mash diets Linear regression 0.0149 0.0250 0.0123 0.0001 0.1505 0.0289 0.5896 0.5848 a,b Means within a column without a common superscript differ signiﬁcantly (P ≤ 0.05). 1 Boneless, skinless breast weight as a percentage of live weight. 2 Small intestine weight (from the gizzard to the ileo-cecal junction) as a percentage of live weight. 3 Fisher’s least signiﬁcant difference value. JAPR: Research Report PARSONS ET AL.: PARTICLE SIZE AND PERFORMANCE 251 Table 5. Inﬂuence of particle size and pellet texture on Feed Passage Time 4.5-wk broiler TMEn (mean ± SD) One hundred forty-four, 1-d-old, straight-run TMEn (kcal/kg) 308 × 344 Ross broilers were allotted to ﬂoor pens Mash treatments (0.69 × 2.44 m) containing fresh wood shavings, Fine corn mash 3,546 ± 67 nipple drinkers, and a feed pan adapted to a hop- Small corn mash 3,625 ± 163 per for 0 to 3 wk. Each pen received a pretest Medium corn mash 3,853 ± 286 Large corn mash 3,689 ± 225 mash starter diet (corn particle size of 870 m) Coarse corn mash 3,476 ± 207 and water for ad libitum consumption. Upon con- LSD1 value — clusion of the 3-wk period, birds were transferred ANOVA 0.0713 to a similar room as that utilized in the metabolism Pelleted treatments Soft pellet 3,256 ± 150b study and 3 birds per cage were placed in each Hard pellet 3,419 ± 93a of 48 raised wire cages for a 10-d adaptation LSD value 162 period. Eight groups of 6 adjacently caged birds ANOVA 0.0492 comprised blocks for a randomized complete P-value for quadratic block design. Six mash diets were manufactured regression of mash diets Quadratic regression 0.0042 utilizing similar formulation and corn particle size a,b as those used in the performance study for each Means within a column without a common superscript differ signiﬁcantly (P ≤ 0.05). of the 5 mash diets (ﬁne, small, medium, large, 1 Fisher’s least signiﬁcant difference value. 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 week), birds were restricted from feed for 24 h. and was fed in mash form using the ﬁne corn Following restriction, feed was provided for 45 particle size to exclude feed-form effects. Each min, and then removed. Those birds not assigned of the 6 diets was randomly assigned to cages a diet received no feed during this time. Total within each block. Diets were fed to birds during excreta were collected for 48 h from the time the adaptation period and fecal samples were of feeding, air-dried, weighed, and ground. All taken to determine percentage acid insoluble ash samples were analyzed in duplicate for gross en- (AIA) from diets without added AIA. At the end ergy  and nitrogen . Retained nitrogen of the adaptation period, birds were feed restricted was calculated and corrected for eventual uric for 24 h. Birds were fed 200 g/cage of the assigned acid formation and oxidation . Nitrogen-cor- experimental diets containing 0.5% AIA . rected TME was calculated using the weight of Feed was provided for a 2-h period, then removed feed consumed, total excreta, gross energy, and and weighed to determine feed intake. A diet retained nitrogen oxidation values. without added AIA corresponding to diets as- Table 6. Inﬂuence of particle size and fat inclusion level on passage time as determined by percentage of acid insoluble ash (AIA) Passage time (h) 1 2 Treatment FI (g) 0 6 8 10 12 14 16 24 30 36 Fine 74.13 0.1332 15.814 10.473 2.630 0.638 1.108 0.522 0.222 0.617 0.399 Small 78.93 0.0270 16.705 10.101 2.543 0.943 0.733 0.213 0.159 0.430 0.384 Medium 65.53 0.0174 13.865 10.466 2.176 0.750 0.965 0.248 0.130 0.428 0.432 Large 80.25 0.0196 15.193 10.704 2.094 1.068 0.738 0.151 0.040 0.669 0.394 Coarse 87.78 0.1872 13.030 7.350 1.795 0.891 0.701 0.249 0.070 0.383 0.339 Soft mash 72.73 0.2549 13.747 9.502 2.765 1.282 0.636 0.124 0.078 0.356 0.233 ANOVA P-values3 0.4682 0.5453 0.2100 0.4982 0.8054 0.6639 0.6731 0.2393 0.1035 0.4258 0.8352 1 Feed intake of diets containing 0.5% AIA per cage. 2 Percentage AIA of excreta resulting from unmarked diets. 3 There were no signiﬁcant differences (P > 0.05). 252 JAPR: Research Report signed to each cage was fed upon removal of diets preference. Fisher’s least signiﬁcant difference containing added AIA. Fecal collection began 6 test was used for multiple comparisons between h after providing diets containing added AIA and mean values. Linear and quadratic regression was continued every 2 h for the following 12 h, then performed with coefﬁcients for unevenly spaced at 24, 30, and 36 h post-AIA administration. Wa- treatments to determine trends among mash diet ter was provided for ad libitum consumption variables. Nonsigniﬁcant quadratic terms were re- throughout the experiment. Collected excreta moved from the model. Trends in particle size were stored and analyzed for DM  and AIA preference were determined using a regression . Acid insoluble ash measurements were cor- model with block and treatment as categorical rected for AIA contained in diets without values and time as a continuous variable. Con- added AIA. trasts were used to compare 3, 6, 9, or 12 h to time zero. In all analyses, α was 0.05. Particle Size Preference RESULTS AND DISCUSSION One hundred twenty 1-d-old, straight-run 308 × 344 Ross broilers were fed a starter mash pretest Particle Size diet (1,042 m) from 0 to 3 wk of age. Birds Broiler feed intake (FI) increased (P = were then transferred to a room similar to that 0.0001) and feed efﬁciency (FE) decreased (P = used in the TMEn study and placed in 40 raised 0.0013) as dietary corn particle size increased wire cages (3 birds/cage) for a 10-d adaptation (Table 3). Broilers fed diets containing coarse period. Each cage of 3 birds constituted an experi- corn had signiﬁcantly increased FI and decreased mental unit. Eight groups of 5 adjacent cages FE compared with birds fed most other mash provided blocks for a randomized complete block diets. Hetland et al.  reported increased FI design. Upon conclusion of the adaptation period, when feeding diets with high inclusions of whole birds (4.5 wk of age) were restricted from feed cereals. The authors remarked that excessive feed for 24 h. The 5 experimental mash diets that wastage contributed to the increased FI. Exces- differed in particle size (Table 1) were randomly sive feed wastage was not observed in the current assigned to cages within each block. Experimen- study. Past literature has also suggested that broil- tal diets were supplied in 1.0-kg aliquots. Water ers may not be able to efﬁciently utilize large corn was provided ad libitum. A 100-g feed sample particles due to underdeveloped gastrointestinal was taken from each cage to determine initial diet tracts [1, 34]. In the current study, linear regres- particle size. Homogeneous feed samples (100 g) sion indicated that increased corn particle size were taken following feed administration at 3-h signiﬁcantly increased nitrogen retention. Simi- intervals for a 12-h period. Homogeneity of feed larly, increased corn particle size showed trends samples was created by 30 s of manual stirring. toward increased lysine retention (P = 0.0669). Particle size analysis was performed on all test Hence, broilers fed larger particle corn did not samples . Preference was determined by com- seem to be affected by underdeveloped gastroin- paring the average particle size at each time point testinal tracts. Broilers fed coarse corn had sig- with the initial average particle size of the as- niﬁcantly lower FE compared with broilers fed signed diet. Increases in diet particle size over diets containing ﬁne, small, or medium corn. time indicate a preference for smaller particles Breast weight and breast weight as a percent- and vice versa. age of live weight decreased (P = 0.0149 and All experimental protocols were approved by 0.0250, respectively) as dietary corn particle size the West Virginia University Animal Care and increased (Table 4). Conversely, gizzard weight Use Committee (ACUC # 02-1002). and gizzard weight as a percentage of live weight increased (P = 0.0123 and 0.0001, respectively). Statistical Analysis Fat pad weight per se was not signiﬁcantly af- The GLM procedure of SAS  was used fected; however, fat pad weight as a percentage to determine effects of particle size and pellet of live weight increased (P = 0.0289) as dietary texture on performance, carcass characteristics, corn particle size increased. Differences in fat pad TMEn, nutrient retention, feed passage time, and weight as a percentage of live weight may have PARSONS ET AL.: PARTICLE SIZE AND PERFORMANCE 253 Table 7. Indication of preference determined by average particle size ( m) of diets as consumed over time Time of collection (h) Treatment Initial 3 6 9 12 Fine 863.875 885.875* 868.625 848.5 797.375* Small 926.5 975.125* 934.125 907.5 857.625* Medium 943.125 957 932.625 897* 832.75* Large 1,065.25 1,073.25 1,034.625 997.125* 932.375* Coarse 1,514.875 1,496* 1,495.5 1,556.875 1,405.25* *Means differ signiﬁcantly from the initial average particle size for that row (P < 0.05). been confounded by larger changes in live weight, had numerically the highest AIA percentages at breast weight, and gizzard weight. Nir et al.  6 h, suggesting increased FPT. Conversely, the reported a positive relationship between gizzard coarse particle diet had numerically the lowest weight and dietary particle size. Similarly, Healy AIA percentage at 6, 8, and 10 h suggesting a  reported increased gizzard, proventriculus, decreased FPT. Nir et al.  reported that con- and intestinal weights for chicks fed corn ground tent weight of the gizzard was signiﬁcantly less to 900 m compared with that ground to 300 for diets containing small particles compared with m. In the current study, increased grain particle large, suggesting a decreased particle retention size seemed to increase the proportion of feed time. Larger corn particles may have been re- energy utilized for gizzard growth and mainte- tained in the gastrointestinal tract for an increased nance as opposed to breast growth. This specula- time that may contribute to increased nutrient tion is also supported by changes in feed efﬁ- digestion and energy metabolism. ciency (Table 3). Consistent preference trends for feed particles True metabolizable energy values were high among diets were not apparent (Table 7). How- relative to the calculated diet ME of 3,200 kcal/ ever, any particle size preference from the initial kg (Tables 1 and 5). Values might have been high diet particle size would indicate that birds are not in general due to the fast-growing broiler model, consuming a homogeneous mix of ingredients and, therefore, a nutrient proﬁle different from the timed feeding regimen, or high soybean oil inclu- calculated formulation. The medium- and large- sion of all diets. Increasing dietary corn particle particle diets illustrated no particle size preference size resulted in a quadratic effect on TMEn (P = (P > 0.05) for collection times of 3 and 6 h. The 0.0042). Feeding diets containing medium corn lack of particle preference may have contributed particles resulted in the highest TMEn. Hetland et to increased performance. However, all mash al.  reported that starch digestibility increased diets illustrated a signiﬁcant preference for larger when broilers were fed whole wheat compared particles for the 12-h collection period. Portella with ground wheat. The authors attributed in- et al.  reported decreases in the concentration creased starch digestibility to increased gizzard of larger particles in a crumbled diet over time. activity that would increase ingredient grinding In summary, broilers obtained digestive bene- and mixing. In the current study, the efﬁciency ﬁts from consuming diets containing medium to of nitrogen and lysine retention of broilers also coarse particle corn (i.e., 1,042 to 2,242 m). In suggested beneﬁts of large particle feeding (Ta- addition, broilers may consume a more balanced ble 3). nutrient proﬁle from medium and large particle Feed passage time (FPT) data are illustrated corn (i.e., 1,042 and 1,109 m) due to lack of at different collection times by the average per- particle size preference. However, feeding coarse centage AIA of excreta in Table 6. Cage FI did not corn (i.e., 2,242 m) may increase gizzard growth differ among diets (P = 0.4682). The maximum and maintenance to an extent that compromises excretion of AIA for all diets occurred during the performance. 6- and 8-h collection periods. Jensen et al.  reported maximum excretion of chromic oxide at Pellet Texture similar times. Particle size did not signiﬁcantly All physical characteristics of the pelleted affect FPT. However, ﬁne and small particle diets diets were similar with the exception of texture 254 JAPR: Research Report as determined by breaking force (Table 2). Mean corn was assessed for feed passage time, due to breaking force for pellets containing commercial its high soy oil inclusion (i.e., 6.3%). Feed pas- binder was greater than that of pellets containing sage time did not indicate signiﬁcant treatment added water, 1,856.37 and 1,662.45 g respec- differences; however, the soft mash formulation tively, producing a comparatively harder texture. illustrated numerically decreased feed passage The high percentages of ﬁnes for both diets are time compared with the ﬁne corn particle diet for indicative of commercial pellet manufacture post 6- and 8-h collection periods (Table 6). cooling and transport . The current ﬁndings imply that a harder pellet Broilers fed hard pellets had signiﬁcantly texture may produce beneﬁcial digestive and sub- greater live weight gain and FE than those fed sequent performance effects compared with pel- soft pellets (Table 3). Performance beneﬁts of lets of softer texture. The hard pellet texture hard pellets compared with soft pellets may be (1,856 g of breaking force) was not hard enough derived by similar mechanisms as observed with to produce carcass characteristic effects that were increased corn particle size of mash diets. Nitro- gen and lysine retention were signiﬁcantly im- detrimental to performance but was able to pro- proved for broilers fed hard pellets compared with duce favorable digestive effects despite being broilers fed soft pellets. In addition, Table 5 illus- compared with the soft pelleted diet that had a trates that hard pellets produced a signiﬁcant in- higher inclusion of fat. Mateos et al.  suggest crease in TMEn compared with soft pellets. Car- that supplemental fat may enhance the use of cass characteristics were not affected by pellet dietary energy by slowing the rate of passage of texture (P > 0.05; Table 4). Feed passage time diets, creating an extracaloric effect. The precise was not performed on pelleted feed. However, mechanism of pellet texture effects on broiler the soft pellet formulation made with ﬁne particle performance remains unclear. CONCLUSIONS AND APPLICATIONS 1. Feeding broilers medium to coarse particle corn (i.e., 1,042 to 2,242 m) improved nutrient digestion; however, broilers fed coarse particle corn (i.e., 2,242 m) 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. REFERENCES AND NOTES 1. Lott, B. D., E. J. Day, J. W. Deaton, and J. D. 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The mean geometric particle size feed particle size preference by broilers. Can. J. Anim. Sci. 68:923–930. and log normal geometric standard deviation were calculated as de- scribed by McEllhiney . 37. Scheideler, S. E. 1991. Pelleting is important for broilers. Pages 1–7 in Proc. 18th Annu. Carolina Poult. Nutr. Conf., Charlotte, 21. Maxibond–urea-formaldehyde resin and calcium sulfate to aid NC. North Carolina State Univ., Raleigh. in pelleting animal feed and included in the diet at 4 lb/ton. 38. Mateos, G. G., J. L. Sell, and J. A. Eastwood. 1982. Rate of 22. American Society of Agricultural Engineers. 1997. ASAE food passage (transit time) as inﬂuenced by level of supplemental fat. S269.4, Cubes, pellets, and crumbles-Deﬁnitions and methods for Poult. Sci. 61:94–100. determining density, durability, and moisture. Standards 1997. Am. Soc. Agric. Eng., St. Joseph, MI. Due to the use of a 5/32 × 1.25 in. 39. McEllhiney, R. R. 1994. Determining and expressing particle die, pellets were sifted in a No. 6 American Society for Testing and size. Pages 545–547 in Feed Manufacture Technology IV. American Materials (ASTM) screen. Five hundred grams of sifted pellets was Feed Industry Association, Inc., Arlington, VA. placed in a dust-tight enclosure and tumbled for 10 min at 50 rpm. The enclosure was of the dimensions 5 × 12 × 12 in., with a 2 × 9 40. Avaigen, Hunstville, AL. in. plate afﬁxed diagonally along 1 of the 12 × 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 Acknowledgments pellets after tumbling by the weight of pellets before tumbling, then This study was ﬁnanced by Hatch funds allocated to West Virginia multiplying by 100. The modiﬁed pellet durability index was deter- University, Project No. H-435 and USDA-NRI 2002-35208-11580. mined in a similar manner with the exception of adding 5, 13-mm The authors acknowledge Fred Roe, Bill Miller, and Bill Jones for hex nuts to the pretumbled sample to obtain added pellet pressure. assistance with animal welfare. Mark Nazelrodt and Pilgrim’s Pride 23. American Society of Agricultural Engineers (ASAE). 1983. Corporation are appreciated for feed manufacture and broiler chick Methods of determining and expressing ﬁneness of feed materials by support.