Development and evaluation of a pelleted feedstuff containing condensed corn steep liquor and raw soybean hulls for dairy cattle diets

Animal Feed Science and Technology 107 (2003) 75–86 Development and evaluation of a pelleted feedstuff containing condensed corn steep liquor and raw...
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Animal Feed Science and Technology 107 (2003) 75–86

Development and evaluation of a pelleted feedstuff containing condensed corn steep liquor and raw soybean hulls for dairy cattle diets夽 J.M. DeFrain a,1 , J.E. Shirley a,∗ , K.C. Behnke b , E.C. Titgemeyer a , R.T. Ethington c a

Department of Animal Sciences and Industry, Kansas State University, Manhattan, KS 66506, USA Department of Grain Science and Industry, Kansas State University, Manhattan, KS 66506, USA c Minnesota Corn Processors, LLC, Marshall, MN 56258, USA

b

Received 5 February 2002; received in revised form 18 February 2003; accepted 18 February 2003

Abstract A novel product containing raw soybean hulls (RSH) and corn steep liquor (CSL) was developed and evaluated. Feed processing techniques evaluated were: (1) CSL inclusions (0, 50, 80, 100, 120, 150, 200, and 250 g/kg of pellet dry matter [DM]) at the pellet mill conditioner; (2) CSL inclusions (100, 150, and 200 g/kg of pellet DM) using an expander as the sole source of thermal processing; and (3) treating a 200 g/kg CSL inclusion (DM basis) with expander cone pressures of 10.5, 14.0, 17.6, and 21.0 kg/cm2 . Improvements in pellet quality were observed with increasing amounts of CSL independent of processing method. However, both pellet durability and electrical energy efficiencies during processing were optimized when CSL was applied at the pellet mill conditioner at a rate to produce pellets containing 750 g/kg RSH and 250 g/kg CSL (raw soybean hull-condensed corn steep liquor pellet (SHSL), DM basis). Increasing the concentration of CSL (up to 250 g/kg of pellet DM) resulted in higher pellet equilibrium moisture contents (EMCs) and reduced the urease activity in RSH. The chemical compositions of RSH, CSL, and SHSL are presented. © 2003 Elsevier Science B.V. All rights reserved. Keywords: Soybean hulls; Condensed corn steep liquor; Byproduct

Abbreviations: CSL, corn steep liquor; DM, dry matter; EMC, equilibrium moisture content; NFC, non-fiber carbohydrate using 100 − (%CP + %NDF + %ether extract + %ash); PDI, pellet durability index; RH, relative humidity; RSH, raw soybean hulls; SHSL, raw soybean hull-condensed corn steep liquor pellet 夽 Contribution number 02-220-J from the Kansas Agricultural Experiment Station, Manhattan, KS, USA. ∗ Corresponding author. Tel.: +1-785-532-1218; fax: +1-785-532-5681. E-mail address: [email protected] (J.E. Shirley). 1 Present address: Dairy Science Department, South Dakota State University, Brookings, SD 57007-0647, USA. 0377-8401/03/$ – see front matter © 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0377-8401(03)00068-3

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1. Introduction In the Midwest United States, 20% of lactating dairy cattle diets contain byproduct feedstuffs (Mowrey and Spain, 1999), thus, dairy cattle play an integral role in the ecosystem by serving as nature’s biological recyclers. Incorporating byproducts into dairy diets may also increase ration quality and reduce feed costs. Factors negating the advantages of byproducts in dairy diets include local availability, seasonality of supply, shipping costs, storage life, and variability in chemical composition. Most of the grain processing byproducts produced in the Midwest United States originate from corn, soybeans, and wheat. Two major byproducts are raw soybean hulls (RSH) and condensed corn steep liquor (CSL), a liquid byproduct comprised of steep water (water containing the soluble materials from the steeping process) and distillers solubles. Raw soybean hulls are a highly digestible source of structural fiber, containing minimal amounts of lignin (Garleb et al., 1988). Previous research with soybean hulls in dairy diets suggests they possess an energetic value similar to corn (Nakamura and Owen, 1989), and others have described their ability to replace forage fiber (Grant, 1997). On the other hand, CSL contains inexpensive sources of carbohydrates, soluble protein, vitamins, and minerals (Hull et al., 1996). Corn steep liquor has improved body weight and condition when used as a protein supplement for beef cattle grazing dormant native range (Wagner et al., 1983). In vitro work by Filho (1999) indicated CSL increases starch digestion but decreases cellulose digestion. The chemical composition of these two byproducts (RSH and CSL) appear to be complementary to each other. Combining them would likely reduce transportation costs and provide an energy dense, fibrous co-product for lactating dairy cattle diets. We are unaware of previous attempts to combine these two byproducts into a pelleted feedstuff for dairy cattle diets. The objectives of our study were to determine the optimal processing method for combining CSL and RSH into a pelleted feedstuff and characterize the chemical properties of pellets containing different concentrations of RSH and CSL.

2. Materials and methods 2.1. Feed processing experiments Four experiments were conducted at the Kansas State University pilot feed mill (Manhattan, KS) to determine the optimal procedure to combine CSL and RSH into a pelleted feedstuff. All experiments were conducted using a 30 hp California Pellet Mill 1000 series “Master HD” model (Crawfordsville, IN) equipped with a standard conditioner and a 4.76 × 31.75 mm die (hole diameter × effective die thickness). A liquid pump (Robins and Myers, Inc., Springfield, OH) was used to propel CSL into the pellet mill conditioner (or expander). All pellets were conveyed to a California Pellet Mill horizontal cooler equipped with a steam heat exchanger, which generated a temperature of 104 ◦ C to assist in drying of the pellets. The pellets remained in the horizontal cooler for approximately 6.5 min after which they were conveyed by bucket elevator to a sack-off bin, packaged into paper bags (approximately 18 kg per bag), placed on pallets, and shipped to the KSU Dairy Teaching and Research Center, Manhattan, KS.

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The pellet mill feeder was calibrated by incrementally increasing the flow rate of RSH and recording the respective rpm using a photo/contact digital tachometer (Fisher Scientific, 05-028-23, Pittsburgh, PA). Throughput was recorded in 10 s intervals, in triplicate, at four different feeder screw speeds. A linear trend line was established by regressing throughput on rpm of the feeder screw. This model was used to predict flow rates of RSH and mixer mash to the pellet mill conditioner at speeds within the linear range. The liquid pump was calibrated in the same manner to determine the flow rate of CSL to the pellet mill conditioner and expander. Corn steep liquor was pumped into a tared weigh bucket at various pump speeds. The rpm of the liquid pump and CSL output (kg/10 s) was recorded in triplicate at various rpm and a trend line was fit to the data, which allowed the model to predict flow rates at pump speeds within the linear range. Pellet quality was measured using the standard determination for pellet durability index (PDI; ASAE, S269.3, 1987) and a modified procedure using five, 13 mm hexagonal nuts added with the pellets. This durability index describes the percentage of whole pellets that are not degraded to fines after a 10 min agitation. The purpose of the agitation is to simulate handling and conveying of the feed. Electrical data were recorded using an amp–volt meter (Model DMI, Amprobe Instrument, Lynbrook, NY). 2.1.1. Pellet mill conditioner Corn steep liquor was pumped into the pellet mill conditioner where it was blended with RSH. Conditioning speed and temperature remained constant at 28 rpm and 66 ◦ C, respectively. To alter pellet composition, the flow rate of CSL to the pellet mill conditioner was adjusted while the flow rate of RSH remained constant. The speed of the liquid pump was adjusted to produce pellets containing 0, 50, 80, 100, 120, and 150 g/kg CSL on a dry matter (DM) basis. 2.1.2. Mixer mash/conditioner The results from the pellet mill conditioner experiment suggested CSL inclusion levels greater than 150 g/kg (DM basis) could be attained because pellet quality was not compromised by CSL inclusions up to 150 g/kg of pellet DM. However, the liquid pump was not capable of inclusion rates exceeding 150 g/kg of pellet DM so a Forberg paddle mixer (Ontario, Canada) was utilized to mix CSL and RSH at 100 and 900 g/kg (DM basis), respectively. This mixer mash was conveyed to the pellet mill and the pellet mill feeder screw was re-calibrated in the manner previously described. To manufacture pellets containing CSL concentrations of 150, 200, and 250 g/kg on a DM basis, additional CSL was applied to the mixer mash at the pellet mill conditioner. Conditioning speed and temperature were maintained as described for the pellet mill conditioner experiment. 2.1.3. Expander The use of a 100 hp expander (Model OE15.2, Amandus-Kahl, Hamburg, Germany) was evaluated as an alternative method of thermal processing CSL and RSH prior to pelleting. An expander operates similar to a single screw extruder but requires less energy input and less maintenance. The feed is first conditioned and then passed through a thin gap between a cone-shaped device and a cone ring, which provides a secondary, high shear, conditioning process. The amount of thermal processing due to frictional force is controlled

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using a hydraulic cylinder to adjust the width of the gap. A Forberg paddle mixer was used to blend CSL as described for the mixer mash/conditioner experiment. The mixer mash was conveyed to the expander and cone pressure was maintained at 7.0 kg/cm2 . The flow rate (electronically controlled) of the mixer mash (100 g/kg CSL, 900 g/kg RSH on a DM basis) through the expander remained constant and changes in the flow rate of CSL produced expander mash containing 100, 150, and 200 g/kg CSL (DM basis). The expander mash bypassed the pellet mill conditioner and was deposited directly into the pellet die chamber. The final experiment evaluated the effect of expander cone pressure on pellet quality and processing parameters. The flow rate of CSL remained constant, so that expander mash contained 800 g/kg RSH and 200 g/kg CSL (DM basis). The expander mash was then treated with cone pressures of 10.5, 14.0, 17.6, and 21.0 kg/cm2 prior to delivery to the pellet die chamber. 2.2. Product evaluation 2.2.1. Chemical composition Random samples of RSH, CSL, and a pellet containing 750 g/kg RSH and 250 g/kg CSL (raw soybean hull-condensed corn steep liquor pellet (SHSL), DM basis) were collected at approximately 15 min intervals during the mixer mash/conditioner experiment and analyzed by Northeast DHI Forage Testing Laboratory, Ithaca, NY. Crude protein was measured as Kjeldahl N × 6.25. Streptomyces griseus enzymatic technique was used to measure protein degradability using the method of Roe and Sniffen (1990). In addition, NDF, ADF, and lignin were measured using the ANKOM A200 (ANKOM Technology Corp., Fairport, NY) filter bag technique. Acid detergent fiber solutions were according to AOAC (973.18 C, 1997) whereas NDF was according to Van Soest et al. (1991) with the addition of 4 ml of alpha amylase and 20 g sodium sulfite. Ether extract was measured using the automated Tecator Soxtec System HT6 (FOSS North America, Eden Prairie, MN). Non-fiber carbohydrate (NFC) was calculated by difference using the equation NFC(%) = 100−(%CP +%NDF + %ether extract + %ash). Ingredient TDN was calculated using the equations of Weiss et al. (1992). The NEL of concentrates was calculated according to NRC (1988). Separate samples were hydrolyzed in 6N HCl for 24 h at 105 ◦ C, and concentrations of individual amino acids measured. Amino acids were separated using cation exchange chromatography, and measured by fluorimetry following post-column o-phthalaldehyde derivitization (Beckman System Gold; Beckman, Inc., Palo Alto, CA). 2.2.2. Urease activity Samples containing 0, 50, 100, 150, 200, and 250 g/kg CSL (DM basis) obtained from the pellet mill and mixer mash conditioner experiments were measured for urease activity using SOY-CHEK (Alteca Ltd., Manhattan, KS). A 2 g sample was saturated with SOY-CHEK, gently stirred, and allowed to stand for 5 min. Samples were then scored using the scale provided (1 = very active; 6 = fully cooked). Furthermore, samples were ground using a Wiley mill (1 mm screen), and urease activity was measured using the AACC method for urease activity (AACC, Method 22-90, 1983). This procedure is based upon change in pH (relative to blank), a higher pH change indicating higher urease activity.

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2.2.3. Equilibrium moisture content Equilibrium moisture content (EMC) was determined on pellet samples obtained from the mixer mash/conditioner experiment. Samples contained four levels of CSL (100, 150, 200, and 250 g/kg DM). Two environmentally controlled chambers, located at the Kansas State University Grain Storage Research Center, Manhattan, KS, were maintained at 10 and 30 ◦ C to simulate winter and summer conditions. Ten dessicators were used to maintain five different relative humidity (RH) levels within each chamber (in duplicate). Saturated salt solutions used to control RH were prepared according to Winston and Bates (1960). Relative humidity levels and (salts) used were 67% (NaBr), 75% (NH4 NO3 ), 82% (NH4 NO3 + AgNO3 ), 85% ((NH4 )2 SO4 ), 90% (KCl) in the 10 ◦ C chamber and 69% (NaNO2 ), 71% (Na2 CrO4 ·4H2 O), 77% (NaCl+KCl), 81% (NaCl), 86% ((NH4 )2 SO4 ) in the 30 ◦ C chamber. Pellet samples were air-equilibrated in the laboratory at 20 ◦ C to establish a homogeneous DM (93 g/kg). Samples (∼9.5 g) of each CSL inclusion level were placed in baskets made from fine wire screen. Each CSL inclusion level was represented in duplicate within each chamber and dessicator. Weights of the sample and wire basket were recorded at the start of the experiment and at 3 days intervals. When the weight change was less than 0.005 g, EMC was calculated as ((initial weight − equilibrated weight)/equilibrated weight) × 100. Average EMC was calculated for each level of CSL within each temperature and RH.

3. Results and discussion 3.1. Feed milling experiments The inclusion of CSL (up to 250 g/kg DM) during the pellet mill and mixer mash/conditioner experiments improved both standard and modified PDI (Tables 1 and 2). Generally, ingredients high in protein and fiber are more easily pelleted (Boerner, 1992), hence the protein and fiber of CSL and RSH likely complemented each other during the pelleting process. Researchers have recognized the importance of protein in the binding properties of feeds. Briggs et al. (1999) reported an increase in pellet quality when protein was Table 1 Effect of corn steep liquor on feed mill performance and pellet quality during the pellet mill conditioner experiment Item

Condensed corn steep liquor (g/kg of dry matter) 0

50

80

100

120

150

Production rate (kg/h)

489

534

565

587

609

644

Electrical energy Amperes Volts MJ/tonne

18.2 436.4 76.9

17.2 436.3 66.6

16.4 436.4 60.2

15.6 436.4 54.9

15.1 435.8 51.4

14.6 435.7 46.8

91.3 88.6

95.6 94.8

96.2 95.0

96.6 96.2

96.1 96.6

96.7 96.2

PDIa PDImb a b

Standard pellet durability index. Modified pellet durability index using five 13 mm hexagonal nuts.

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Table 2 Effect of corn steep liquor on feed mill performance and pellet quality during the mixer mash/conditioner experiment Item

Condensed corn steep liquor (g/kg of dry matter) 100

150

200

250

Production rate (kg/h)

387

424

467

515

Electrical energy Amperes Volts MJ/tonne

15.9 438.2 85.4

14.8 438.9 72.6

14.2 438.9 63.1

13.2 438.7 53.1

96.7 97.0

97.1 96.5

97.1 96.8

97.8 97.2

PDIa PDImb a b

Standard pellet durability index. Modified pellet durability index using five 13 mm hexagonal nuts.

increased from 180 to 240 g/kg of pellet DM. Protein’s effect on pellet durability was also observed by Wood (1987). Wood (1987) reported improvements in pellet durability when using raw soya protein as opposed to denatured soya protein. The addition of water also improves pellet quality. Moritz et al. (2001) reported improvements in PDI when water was added to broiler diets based on corn and soybean meal. The CSL in our study contained approximately 450 g/kg moisture, thus it too likely contributed to the observed improvements in PDI. Energy consumption for the pellet mill was 21.7 and 15 kWh/tonne for pellets containing 0 and 250 g/kg CSL (DM basis), respectively. Moisture contributed by CSL and steam derived from steam conditioning would provide lubrication during pelleting that would reduce roll wear, reduce electrical energy expenditure, and extend the life of the die. Corn steep liquor additions up to 250 g/kg DM increased production rate without sacrificing pellet quality during the pellet mill conditioner and mixer mash/conditioner experiments. Increasing the level of CSL improved standard and modified PDI during the expander experiment (Table 3). Expanders are known to improve pellet quality, production capacity, and feed hygiene (Fairchild, 1994). During the expander experiment, standard PDI was minimally affected by CSL, but modified PDI increased from 93.4 to 97.3% for pellets containing 100 and 200 g/kg CSL, respectively. Similar to the pellet mill conditioner experiments, pellet mill energy consumption was 14.4 and 11.1 kWh/tonne for 100 and 200 g/kg CSL (DM basis) inclusions, respectively, but expander energy use was not affected. As expected, increasing expander cone pressure resulted in an increase in energy consumption by the expander whereas pellet mill energy consumption was unaffected by increasing cone pressure (Table 4). Increasing expander cone pressure did not influence standard and modified PDI. Traylor et al. (1999) reported increases in standard PDI (P < 0.05) and minimal improvements in modified PDI when high fiber (500 g/kg wheat middlings, as-fed) diets were treated with cone pressures of 0, 11.7, 24.4, and 35.2 kg/cm2 . Contrary to our results, Traylor et al. (1999) reported a linear decrease in pellet mill electrical energy consumption as cone pressure increased. Differences between our results and those of Traylor et al. (1999) could be attributed to differences in mois-

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Table 3 Effect of corn steep liquor on feed mill performance and pellet quality during the expander experiment Item

Corn steep liquor inclusion (g/kg of dry matter) 100

150

200

Production rate (kg/h)

636

698

768

Electrical energy Expander Amperes Volts MJ/tonne

54.7 442.0 180.0

59.7 441.8 178.6

55.3 442.1 150.6

Pellet mill Amperes Volts MJ/tonne

15.7 437.4 51.0

14.9 437.6 44.3

14.6 437.5 39.3

94.7 93.4

96.3 95.8

97.6 97.3

PDIa PDImb a b

Standard pellet durability index. Modified pellet durability index using five 13 mm hexagonal nuts.

ture content of the expander mash entering the pelleting die chamber. Our results suggest expander technology is not the most energy-efficient method to produce a pelleted feedstuff containing RSH and CSL and may not be feasible under these operating conditions.

Table 4 Effect of expander cone pressure on feed mill performance and pellet quality during the expander cone pressure experiment Item

Expander cone pressure (kg/cm2 ) 7.0

10.5

14.0

17.6

21.0

Production rate (kg/h)

768

768

768

768

768

Electrical energy Expander Amperes Volts MJ/tonne

55.3 442.1 150.6

60.5 443.7 165.4

63.8 443.5 174.3

72.1 443.3 197.0

90.8 442.5 247.3

Pellet mill Amperes Volts MJ/tonne

14.6 437.5 39.3

14.9 439.5 40.4

14.8 439.4 40.0

14.9 439.4 40.4

13.9 439.1 37.6

97.6 97.3

97.2 96.8

97.4 97.0

97.7 97.4

98.0 97.3

PDIa PDImb a b

Standard pellet durability index. Modified pellet durability index using five 13 mm hexagonal nuts.

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Table 5 Nutrient composition of raw soybean hulls, corn steep liquor, and a pellet containing 750 g/kg raw soybean hulls, 250 g/kg condensed corn steep liquor (SHSL, dry matter basis) Item

Raw soybean hulls

NEL (MJ/kg)

6.27

Condensed corn steep liquor

7.81

SHSL Predicteda

Measured

6.64

6.72

DM (g/kg) CP (g/kg) Soluble proteinb RUP (g/kg) ADF (g/kg) NDF (g/kg) Ether extract (g/kg) Ash (g/kg) NFC (g/kg) Ca (g/kg) P (g/kg) Mg (g/kg) K (g/kg) Na (g/kg) S (g/kg)

910 135 320 440 433 587 29 54 195 6.8 1.8 2.7 14.2 0.4 1.2

525 442 920 90 7 23 8 105 424 0.8 20.4 7.5 28.9 1.7 19

814 212 470 323 327 446 24 67 252 5.3 6.5 3.9 17.8 0.7 5.7

870 242 398 360 289 367 25 75 282 4.5 7.5 4.4 19.6 1.8 4.8

Fe (mg/kg) Zn (mg/kg) Mn (mg/kg) Cu (mg/kg)

592 44 30 11

119 101 40 6

474 58 32 10

402 68 36 9

a b

(75% × raw soybean hull nutrient content) + (25% × corn steep liquor nutrient content). Expressed as g/kg of CP.

3.2. Product characterization 3.2.1. Product analysis Nutrient composition of RSH, CSL, and SHSL are presented in Table 5. Raw soybean hulls possessed a nutrient profile similar to that described by NRC (2001). The CSL in our study contained equal proportions of byproducts from starch extraction and ethanol production facilities (Minnesota Corn Processors, Inc., Columbus, NE). According to the nutrient profile, SHSL is best described as a ruminally degradable protein source that is high in fiber. The amino acid composition of RSH, CSL, and SHSL are presented in Table 6. The Leu and Lys concentration of RSH were higher than those reported by NRC (2001). Proportions of essential and non-essential amino acids within RSH and CSL, respectively, were similar, but concentrations of most AA in CSL were at least two times those of RSH. In addition, the Met content of CSL was much greater than that of RSH. According to NRC (2001), the SHSL product is higher in Met than RSH and corn grain but lower than alfalfa hay. Methionine is often the first limiting amino acid in lactating dairy diets (Schwab et al., 1992) and SHSL appears to be a good source, particularly if the product is substituted for a portion of the corn grain in the diet. The effect of CSL on urease activity is shown in Fig. 1. Urease activity, measured using either SOY-CHEK or AACC (1983) method, was reduced as the level of CSL increased in the

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Table 6 Amino acid profiles of raw soybean hulls, corn steep liquor, and a pellet containing 750 g/kg raw soybean hulls, 250 g/kg condensed corn steep liquor (SHSL, dry matter basis) Amino acid

Raw soybean hulls

Condensed corn steep liquor

SHSL Predicteda

Essential Lys His Arg Thr Val Met Ile Leu Phe

Measured

13.4 5.2 10.6 6.9 8.8 8.0 7.7 13.7 7.8

21.9 16.6 27.1 18.0 27.4 10.7 17.6 42.5 17.9

15.5 8.1 14.7 9.7 13.5 3.3 10.2 20.9 10.3

18.5 11.1 18.6 11.4 15.8 2.3 13.1 25.0 13.6

Total EAA

74.9

199.7

106.1

129.4

Non-essential Asx Ser Glx Gly Ala Tyr

20.3 12.0 24.0 14.9 9.1 7.5

41.5 24.2 79.1 26.4 36.9 15.6

25.6 15.1 37.8 17.8 16.1 9.5

32.4 17.6 49.5 19.0 18.1 10.7

Total NEAA

87.8

223.7

121.8

147.3

Total amino acids

162.7

423.4

227.9

276.7

The values are in g/kg of DM. EAA: essential amino acids; NEAA: non-essential amino acids. a (75% × raw soybean hull AA content) + (25% × corn steep liquor AA content).

Fig. 1. Effect of corn steep liquor on urease activity of raw soybean hulls as measured by change in pH (䊊, AACC, 1983) and SOY-CHEK index ( , Alteca Ltd., Manhattan, KS).

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Fig. 2. Equilibrated moisture content of pellets containing raw soybean hulls and 10 (䉫), 15 (䊊), 20 (+), and 25 ( ) g/kg CSL (DM basis) at 10 ◦ C. Standard errors were 0.20, 0.15, 0.32, and 0.11, respectively.

RSH/CSL mixture. Feed moisture content and duration of thermal processing are known to denature protein and reduce or inhibit urease activity in soybean products (McNaughton and Reece, 1980). Because the conditioning temperature and time were maintained throughout all CSL inclusions, their effects on urease activity were deemed negligible. The addition of 250 g/kg CSL lowered pellet pH from 6.5 to 4.7, which may be responsible for the inhibitory effect of CSL on urease activity. 3.2.2. Equilibrium moisture content Equilibrium moisture content of pellets containing 100, 150, 200, and 250 g/kg CSL (DM basis) at 10 and 30 ◦ C are shown in Figs. 2 and 3, respectively. Hygroscopicity is the tendency of a product to absorb or take up water, largely influenced by surrounding environmental conditions. Determining the EMC of feedstuffs allows feed manufacturers

Fig. 3. Equilibrated moisture content of pellets containing raw soybean hulls and 10 (䉫), 15 (䊊), 20 (+), and 25 ( ) g/kg CSL (DM basis) at 30 ◦ C. Standard errors were 0.21, 0.02, 0.25, and 0.01, respectively.

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and distributors to approximate the amount of moisture a given feed might absorb when exposed to different environmental conditions during storage and/or transport. When feeds are highly hygroscopic, they become more susceptible to mold growth and development. Furthermore, increases in moisture content have also led to reductions in pellet and cube durabilities (Fasina and Sokhansanj, 1992). Throughout our EMC determinations, visible observations were made to detect appearance of mold formation on pellet surfaces. Mold was particularly evident on pellets stored at higher temperatures and RH. Pellets, independent of CSL inclusion level, stored at 30 ◦ C with RH > 77% molded 15 days after initiation of the study and were not included in EMC calculations. Pellets stored at 10 ◦ C yielded higher EMC at similar RH and pellet CSL concentrations when compared to pellets stored at 30 ◦ C. Higher CSL inclusions resulted in higher EMC as RH increased, suggesting that the hygroscopicity of CSL is relatively high. However, data from Lamond and Graham (1993) showed that EMC estimations at higher (>70%) RH are more sensitive to error. Further research is needed to investigate the application of mold inhibitory products during the production of SHSL.

4. Conclusions Adding CSL (up to 250 g/kg DM basis) during the pelleting of RSH using a standard conditioner decreased electrical energy expenditure during the pelleting process, increased production rates and pellet durability index, and reduced the urease activity of RSH. Although similar improvements in production rates and pellet quality were observed from the use of expander technology, the additional electrical energy expenditure did not justify its use as an alternative method of thermal processing. Independent of processing method, CSL additions reduced the urease activity of RSH. Equilibrium moisture content evaluations suggest that the hygroscopicity of CSL is relatively high and mold inhibitory studies are warranted.

Acknowledgements Funding was provided by Minnesota Corn Processors, LLC, Marshall, MN and the Kansas Agricultural Experiment Station. The authors express appreciation to Cheryl K. Armendariz for laboratory assistance and personnel at the Kansas State University Feed Processing Center and Grain Storage Center for their contributions during the completion of these experiments.

References AACC, 1983. Approved Methods of the American Association of Cereal Chemists, vol. I. St. Paul, MN. ASAE, 1987. Wafers, pellets, crumbles—definitions and methods for determining density, durability, and moisture content. ASAE Standard S269.3, Agricultural Engineers Yearbook of Standards. American Society of Agricultural Engineers, St. Joseph, MI, p. 318.

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