Grinding and Pelleting Responses of Pearl Millet-Based Diets 1

2005 Poultry Science Association, Inc. Grinding and Pelleting Responses of Pearl Millet-Based Diets 1 W. A. Dozier, III,*,2 W. Hanna, and K. Behnke *United States Department of Agriculture, Agriculture Research Service, Poultry Research Unit, PO Box 5367, Mississippi State, Mississippi 39762-5367; Department of Crop and Soil Sciences, University of Georgia, Tifton, Georgia 31793-7448; and Department of Grain Science and Industry, Kansas State University, Manhattan, Kansas 66506 Primary Audience: Feed Mill Managers, Live Production Personnel, Nutritionists, Quality Control Personnel SUMMARY Pearl millet grain has been reported as an alternative feed ingredient for broiler chickens, but little information exists on the feed processing parameters associated with this cereal grain. This study examined grinding and pelleting responses of pearl millet-based diets. Four treatments were used in the grinding phase, which consisted of grinding corn through a hammer mill screen hole of 4.0 mm and pearl millet ground through a hammer mill screen hole of 4.0, 3.2, or 2.4 mm. In the pelleting phase, a broiler grower diet (20% CP) was manufactured. The treatment structure was a 2 (pearl millet inclusion rate) 3 (particle sizes of ground pearl millet) factorial arrangement with a corn-soybean meal positive control. The main factors consisted of 2 concentrations of millet in the diet at 25 or 50% pearl millet feed and grinding pearl millet through a 4.0-, 3.2-, or 2.4- mm hammer mill screen hole. All grain used during pelleting was derived from the grinding process. Electrical usage during grinding was greater with corn compared with pearl millet. Reducing the hammer mill screen hole size of pearl millet increased electrical usage and decreased the mean particle diameter of pearl millet. Particle size was not affected by grain type. Decreasing the grind size of pearl millet improved pellet durability index and percentage of fines. We concluded that pearl millet-based diets have acceptable grinding and pelleting performance compared with a typical corn-soybean meal diet. Key words: feed processing, grinding, particle size, pearl millet, pellet quality 2005 J. Appl. Poult. Res. 14:269 274 DESCRIPTION OF PROBLEM Pearl millet is a drought-tolerant grain crop [1]. It is very efficient in producing acceptable grain yields during drought conditions, whereas a limited amount of rainfall typically impairs grain yield of corn. Unlike other cereal grains, pearl millet appears to be tolerant of acidic soils with low fertility. In the southeastern United States, the soils are acidic and droughts are common. These less-than-favorable growing conditions could potentially increase the demand for pearl millet production under dry-land systems compared with corn or grain sorghum. 1 Mention of trade names or commercial products in this publication is solely for the purpose of providing specific information and does not imply recommendation or endorsement by the USDA. 2 To whom correspondence should be addressed: bdozier@msa-msstate.ars.usda.gov.

270 Pearl millet contains a higher content of CP than corn [2, 3, 4], whereas the metabolizable energy value is similar between the 2 cereal grains [5]. Growth response of broilers fed pearl millet-based diets is similar when compared in birds provided corn-based diets [4, 5, 6, 7]. Because pearl millet has been demonstrated as an alternative feed ingredient for broiler diets, commercial production of pearl millet is warranted. Nearly all feeds provided to broiler chickens are in whole pellet or crumble form [8]. Utility usage represents a significant proportion of the associated costs with feed manufacturing [9]. The whole grain size of pearl millet is much less than corn. This difference in grain size may influence energy usage during feed manufacturing. To our knowledge, however, grinding and pelleting responses of pearl milletbased diets has not been reported in the literature. The objective of this study was to examine the effects of grinding and pelleting responses of pearl millet-based diets. Grinding measurements consisted of production rate, electrical consumption, and particle size, whereas production rate, electrical consumption, and pellet quality assessments were determined in the pelleting phase of the study. MATERIALS AND METHODS Grinding Procedures Three tons of pearl millet grain (TiftGrain 102) were shipped to the Grain Science Department at Kansas State University (Manhattan, KS) from the Coastal Plain Experiment Station (Tifton, GA). During the grinding process, grain was ground through a 22.4-kW Jacobson hammer mill [10] using a screen with 4.0-, 3.2-, or 2.4-mm holes. The treatments consisted of grinding corn using a hammer mill screen with holes of 4.0 mm and reducing the grain size of pearl millet with 4.0-, 3.2-, and 2.4-mm screen holes (Table 1). The average particle size (d gw ) was determined by previously established standards [11]. Electrical consumption was measured with a recording amp-volt meter [12]. Temperature change was determined by the difference between temperature of whole grain and the temperature of the ground grain immediately after grinding. JAPR: Research Report TABLE 1. Experimental treatments during the grinding and pelleting processes Grain and process Hammer mill hole size (mm) Grinding 1 Corn 4.0 Pearl millet 4.0 Pearl millet 3.2 Pearl millet 2.4 Pelleting 2 Diet Control 3 4.0 Low pearl millet 4 4.0 Low pearl millet 4 3.2 Low pearl millet 4 2.4 High pearl millet 5 4.0 High pearl millet 5 3.2 High pearl millet 5 2.4 1 Each treatment was replicated 4 times. 2 Each treatment was replicated 3 times. 3 Corn-based diet. 4 Diet was formulated to contain 25% pearl millet. 5 Diet was formulated to contain 50% pearl millet. Pelleting Procedures and Treatments Diets used in the pelleting phase are presented in Table 2. Seven treatments were used that consisted of a corn-based diet and pearl millet included in the diet at 25 or 50% with the pearl millet being ground through hammer mill screen holes of 4.0, 3.2, or 2.4 mm (Table 1). After the grinding process, ingredients were batched and mixed in a horizontal double ribbon mixer for 120 s of dry mixing followed by 180 s of wet mixing. Each batch consisted of 295 kg. Mash feed was conditioned (shaft speed = 100 revolutions per min) and pelleted with a CPM [13] pellet mill. The pellet mill was equipped with a 31.8 mm thick die and 4.8- mm hole diameter. Fines were screened from the whole pellets and weighed. Electrical consumption was measured with a recording amp-volt meter [12]. To compute temperature change after conditioning, the temperature of pellets placed in an insulated container was subtracted from the conditioning temperature. The pellet durability index (PDI) was determined based on a procedure reported previously [14]. Statistical Analysis The analysis of variance procedure of SAS was performed on the experimental data using

DOZIER, III ET AL.: PROCESSING OF PEARL MILLET-BASED DIETS 271 TABLE 2. Composition of the experimental diets Ingredient (%, as is) Control Low pearl millet High pearl millet Ground yellow corn 61.76 38.73 15.85 Soybean meal (48% CP) 32.00 29.83 27.50 Pearl millet 0.00 25.00 50.00 Soy oil 3.25 3.51 3.77 Dicalcium phosphate 1.49 1.49 1.50 Calcium carbonate 0.75 0.73 0.71 Sodium chloride 0.35 0.33 0.31 DL-Methionine 0.15 0.11 0.07 L-Lysine HCl 0.00 0.02 0.04 Mineral-vitamin premix 1 0.25 0.25 0.25 Total 100.00 100.00 100.00 Calculated nutrient analyses CP (%) 20.0 20.0 20.0 Metabolizable energy (kcal/kg) 3,160 3,160 3,160 Calcium (%) 0.86 0.86 0.86 Available phosphorus (%) 0.40 0.40 0.40 Methionine plus cystine (%) 0.80 0.80 0.80 Lysine (%) 1.08 1.08 1.08 1 Guaranteed analysis per kilogram of premix: selenium, 27 mg; manganese, 40,000 mg; iron, 20,000 mg; iodine, 272 mg, zinc, 40,000 mg; retinyl acetate, 635,035 IU; cholecalciferol, 136,085 IU; α-tocopherol acetate, 136 IU; menadione sodium bisulfate, 68 mg; cyano-cobalamin, 1 mg; thiamine mononitrate, 91 mg; riboflavin, 544 mg; pyridoxine hydrochloride, 113 mg; nicotinic acid amine, 268 mg; D-calcium pantothenate, 544 mg; folic acid, 57 mg; D-biotin, 3 mg; choline chloride, 31,750 mg. the general linear models procedure [15]. The design structure in the grinding and pelleting phases used a completely randomized design. In the grinding phase, the treatments were corn (positive control) ground through hammer mill screen holes of 4.0 mm and pearl millet ground through hammer mill screen holes of 4.0, 3.2, and 2.4 mm. Each treatment was replicated 4 times. In the pelleting phase, the treatment structure of 7 experimental diets consisted of a corn base (positive control) and factorial arrangement (pearl millet inclusion rate and hammer mill screen hole) with each treatment being represented by 3 replications. TABLE 3. Effects of hammer mill screen hole size of pearl millet on the grinding process 1 Treatment Electrical Hammer mill screen Production rate consumption 2 Particle Temperature Grain hole size (mm) (kg/h) (kw h/ton) size 3 (µm) change 4 ( C) Corn 4.0 2,171 c 8.5 a 561 b 2.2 c Pearl millet 4.0 3,268 b 4.7 c 628 a 2.6 b Pearl millet 3.2 3,495 a 4.6 c 611 a 2.9 b Pearl millet 2.4 3,257 b 6.0 b 492 c 3.4 a SEM 31 0.1 12 0.1 Planned comparisons Probability Corn vs. average pearl millet (1 df) 0.001 0.001 0.223 0.001 Hammer mill screen size (2 df) 0.001 0.001 0.001 0.004 Linear (1 df) 0.808 0.001 0.001 0.001 Lack of fit (1 df) 0.001 0.001 0.004 0.859 a c Means not followed by a common letter differ significantly based on least significant difference comparisons at P 0.05. 1 Values are least squares means of 4 replications. 2 Electrical consumption was computed based on kw h/ton = (V A 1.73 power factor)/production rate (ton/h) 1,000. The power factor used was 0.85. 3 Particle size determination was conducted based upon the procedure of Baker and Herrman [20]. 4 Temperature change represents the difference in temperature of the grain before and after the grinding process.

272 JAPR: Research Report TABLE 4. Effects of hammer mill screen hole size of pearl millet formulated at 2 dietary inclusion rates on the pelleting process 1 Treatment Hammer Production Electrical Temperature mill screen rate PDI 2 Fines consumption 3 change 4 Diets size (mm) (kg/h) (%) (%) (kw h/ton) ( D) Control 5 4.0 1,681 a 75.2 c 11.0 abc 6.9 b 2.4 Low pearl millet 6 4.0 1,578 b 73.5 c 12.8 ab 7.5 ab 2.9 Low pearl millet 6 3.2 1,735 a 78.9 ab 10.7 bc 7.3 ab 2.5 Low pearl millet 6 2.4 1,672 a 75.9 bc 10.8 abc 7.2 ab 3.2 High pearl millet 7 4.0 1,680 a 75.6 c 11.5 abc 6.9 b 3.0 High pearl millet 7 3.2 1,742 a 76.3 abc 13.0 a 7.4 ab 2.6 High pearl millet 7 2.4 1,667 a 79.4 a 9.8 c 8.0 a 2.4 SEM 36 1.3 0.7 0.3 0.4 Planned comparisons Probability Treatment effect (6 df) 0.013 0.014 0.138 0.364 0.082 Corn vs. average pearl millet (1 df) 0.959 0.240 0.626 0.201 0.232 Pearl millet percentage (1 df) 0.152 0.252 0.968 0.543 0.324 Linear trend of hammer mill screen size (1 df) 0.171 0.013 0.027 0.196 0.640 Linear pearl millet percentage 0.080 0.527 0.850 0.036 0.176 hammer mill screen size (1 df) Lack of fit (2 df) 0.008 0.018 0.043 0.987 0.343 a c Means not followed by a common letter differ significantly based on least significant difference comparisons at P 0.05. 1 Values are least squares means of 3 replications. 2 PDI = pellet durability index. Each sample was sieved for 5 min with a Ro-Tap Shaker; 10-min tumble at 50 revolutions per min; 5 min of sieving; whole pellets were retained on US #8 sieve. 3 Electrical consumption was computed based on kw h/ton = (V A 1.73 power factor)/production rate (ton/h) 1,000. The power factor used was 0.85. 4 Temperature change represents the difference in temperature of the mash during conditioning and the temperature of the pellets after pelleting. 5 Corn-based diet. 6 Diet was formulated to contain 25% pearl millet. 7 Diet was formulated to contain 50% pearl millet. Orthogonal contrasts and least significant difference means comparison procedures [16] were used to interpret differences among treatment means. In the grinding phase, orthogonal contrasts were used to divide treatment effects with 3 df into 1) corn vs. average pearl millet (1 df), 2) linear effect of hammer mill screen hole size on pearl millet (1 df), and 3) lack of fit (differences in 3 hammer mill screen sizes not explained by linear effect; 1 df). In the pelleting phase, the treatment effects with 6 df were divided into 1) corn vs. pearl millet (1 df), 2) pearl millet composition in the diet of 25 vs. 50% (1 df), 3) linear effect of hammer mill screen hole size averaged over both pearl millet inclusion percentages (1 df), 4) linear hammer mill screen hole size pearl millet composition in the diet (1 df), and 6) lack of fit (2 df). Statistical significance was established at P < 0.05. RESULTS AND DISCUSSION Grinding Grinding pearl millet increased (P < 0.001) production rate while using less (P < 0.001) energy as compared with corn (Table 3). In addition, the temperature rise was greater (P < 0.001) after grinding than for corn. Decreasing the hammer mill screen hole diameter to 2.4 mm increased (P < 0.05) electric consumption and temperature (P < 0.05) and decreased (P < 0.05) particle diameter of pearl millet compared with hammer mill screen holes of 3.2 and 4.0 mm. McEllhiney [17] evaluated the effects of grinding corn through hammer mill screen holes of 3.2 and 2.4 mm in a commercial mill on grinding and pelleting measurements. Reducing the hammer mill screen hole sizes from 3.2 to 2.4 mm decreased production rate by

DOZIER, III ET AL.: PROCESSING OF PEARL MILLET-BASED DIETS 273 51% (12.5 vs. 6.1 tons/h), increased energy consumption by 59% (4.3 vs. 10.5 kw h/ton), and increased the temperature by 45% (6 to 11 C). In the present study, decreasing the hammer mill screen hole sizes from 4.0 to 2.4 mm, increased electrical consumption and the temperature by 22 and 23%, respectively, for processing pearl millet grain. Pearl millet grain is much smaller than whole corn grain prior to grinding. Therefore, a small amount of the whole grain of pearl millet was not ground due to the small size of the grain. As a result, less friction might have occurred during the grinding process, leading to reduced energy consumption and temperature rise compared with corn. The average particle size of whole pearl millet prior to grinding was 1.913 mm, and the percentage of whole grain found in the mash after grinding was approximately 10%. Pelleting The inclusion of pearl millet did not alter pellet quality or energy usage compared with the corn-based diet (Table 4). Increasing the amount of pearl millet in the diet did not affect any of the measurements during pelleting. Reducing the particle diameter of pearl millet increased (P < 0.02) the PDI percentage and decreased (P < 0.03) the percentage of fines, but the production rate was unaffected. However, the lack of fit was significant for these 3 variables, which meant the linear trend did not explain the treatment differences well. The re- sponse of decreasing the particle size of pearl millet was influenced by pearl millet inclusion rate, resulting in a significant interaction for electrical consumption (P < 0.04). Cramer et al. [18] reported a relative electrical energy value of 1.60 kw h/ton and a PDI of 42% with a grain sorghum-based diet. These authors did not mention the hammer mill screen hole size that was used to process the grain sorghum. Skoch et al. [19] determined that pelleting a corn-soybean meal diet had a PDI of 87% and energy consumption of 12.7 kwh/ton. The corn had been ground through a hammer mill screen hole size of 3.2 mm. In the present study, the overall average PDI and electrical consumption for the pearl millet-based diets were 76.6% and 7.4 kw h/ton, respectively. When comparing these results with those of Cramer et al. [18] and Skoch et al. [19], it is worthwhile to note that the amount of dietary fat added varied among these studies. Cramer et al. [18] added 5.0% oil to the diet; Skoch et al. [19] did not add fat, and this study used 3.5 to 3.7% added in the diet. Supplemental fat added in the mixer beyond 1% adversely affects pellet quality exponentially; thus, a 1.5% difference in added fat can have a large impact on pellet quality [8]. To our knowledge, published research does not exist on feed milling parameters of pearl millet for comparison. The research of Cramer et al. [18] and Skoch et al. [19] cannot be directly compared with the results presented herein due to dietary fat differences. CONCLUSIONS AND APPLICATIONS 1. Pearl millet had an increased grinding rate and required less energy for grinding compared with corn. 2. Decreasing the particle size with pearl millet resulted in improved PDI percentage and reduced the percentage of fines. 3. Pearl millet-based diets had similar pelleting performance compared with a typical cornsoybean meal control. REFERENCES AND NOTES 1. Lee, D., and W. Hanna. 2002. Pearl millet for grain. Extension Bulletin 1216. University of Georgia, Athens, GA. 2. Burton, G., H. T. Wallace, and K. O. Rachie. 1972. Chemical composition and nutritive value of pearl millet (Pennisetum typhoides (Burm.) Staph. and E. C. Hubbard grain. Crop Sci. 12:187 188. 3. Adeola, O., and J. C. Rogler. 1994. Pearl millet in diets of White Pekin ducks. Poult. Sci. 73:425 435.

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