J. Dairy Sci. 2009. 92:732-738. doi:10.3168/jds.2007-0780
© 2009 American Dairy Science Association ®
Effects of an esterase-producing inoculant on fermentation, aerobic stability, and neutral detergent fiber digestibility of corn silage
T. W. Kang*,
,
A. T. Adesogan*,
S. C. Kim*,,1 and
S. S. Lee
* Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, PO Box 110910, Gainesville, 32611
Division of Applied Life Science and Technology, College of Agriculture, Gyeongsang National University, Jinju 660-701, Korea
1 Corresponding author: kim0113{at}ufl.edu
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ABSTRACT
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This experiment evaluated effects of an inoculant containing esterase-producing bacteria on fermentation, aerobic stability, in situ dry matter digestibility (DMD), and neutral detergent fiber (NDF) digestibility (NDFD) of corn silage. Two corn hybrids grown on adjacent fields [Croplan Genetics 851RR2 (CS1) and Vigoro 61R36 (CS2)] were harvested at approximately 39% dry matter. Each forage was conserved in quadruplicate in 20-L mini silos with or without application of an inoculant at a level to achieve 1.0 x 104 cfu/g of Lactobacillus casei and 1.0 x 105 cfu/g of Lactobacillus buchneri. After 110 d of ensiling, silos were opened and silages were analyzed for chemical composition, fermentation indices, microbial counts, and aerobic stability. In situ DMD, 24-h and 48-h DMD, and NDFD were measured by incubating ground (6-mm) samples in triplicate in each of 2 lactating, fistulated dairy cows fed a corn silage-based diet. Inoculation decreased concentrations of total fermentation acids and lactate, as well as lactate to acetate ratio, and increased propionate concentration compared with the uninoculated control in CS1 but not CS2. Inoculation tended to decrease yeast counts of CS1 but increased yeast counts and tended to increase the mold counts of CS2. Consequently, inoculation improved the aerobic stability of CS1 by 57.3 h (98%) but decreased that of CS2 by 20.5 h (20%). Inoculation also increased the potentially degradable fraction of CS1 and the total degradable fraction, 24-h and 48-h DMD, and 48-h NDFD of CS2. Inoculation of CS1 modified the fermentation, improved the aerobic stability, and increased the potentially degradable DM fraction. Inoculation of CS2 did not affect fermentation, but decreased the aerobic stability and increased the total degradable DM fraction, 24-h and 48-h DMD, and 48-h NDFD.
Key Words: aerobic stability • esterase • neutral detergent fiber digestibility • Lactobacillus buchneri
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INTRODUCTION
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Corn silage is one of the major forage fiber sources in diets of dairy cows in the United States. Because of differences in variety, maturity, growth environment, and management, the NDF concentration of corn silage ranges from about 38 to 52% of DM, and the 48-h NDF digestibility (NDFD) ranges from about 55 to 65% (Dairy One Laboratories, 2008). A 1-percentage-unit increase in NDFD of corn silage has been proposed to elicit a 0.17-kg increase in DM intake and a 0.25-kg increase in 4% FCM yield (Oba and Allen, 1999). Dietary enzyme treatment often increases NDFD and milk production by dairy cows but the results have not been consistent. Based on a review of 41 treatments from 19 published experiments conducted between 1999 and 2006, supplementation with fiber-digesting enzymes increased milk production by 2.3 to 2.7 kg/d when effective, but only 40% of such treatments increased (P < 0.05) or tended (0.05 < P < 0.10) to increase milk production (Adesogan et al., 2007). Virtually all enzyme mixtures tested contained xylanase or cellulase but they had inconsistent effects on fiber digestion. Eun and Beauchemin (2006) reported that addition of a xylanase-esterase enzyme mixture to corn silage increased NDF digestibility by 31%. This mixture increased milk production from dairy cows by 2.7 kg/d when added to dairy cow diets (Adesogan et al., 2007). Recent studies suggest that ferulic acid esterase activity also may improve enzyme-mediated fiber digestion (Yu et al., 2005; Eun and Beauchemin, 2006; Krueger and Adesogan, 2008). More research is needed on effects of esterase addition to forages and dairy cow diets.
Aerobic instability decreases the value of corn silage in dairy cow diets, particularly if silage is fed at a relatively slow rate. This problem can be prevented by addition of Lactobacillus buchneri 40788 at ensiling (Ranjit and Kung, 2000; Driehuis et al., 2001; Adesogan et al., 2003). However, because L. buchneri has been associated with small increases in DM losses and pH in some studies (Kleinschmit and Kung, 2006), homofermentative bacteria have been included with L. buchneri to prevent such problems in certain inoculants (Filya, 2003; Adesogan et al., 2004). An inoculant containing homofermentative bacteria plus ferulic acid esterase-secreting L. buchneri strain PTA 6138 increased NDF digestion and aerobic stability in preliminary studies (Nsereko et al., 2006a, b). The objective of this study was to determine how this inoculant would affect fermentation indices, fiber digestibility, and aerobic stability of 2 corn silages.
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MATERIALS AND METHODS
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Silage Production
Two corn silages were produced from 2 corn hybrids [Croplan Genetics 851RR2 (CS1), Croplan Genetics, St. Paul, MN; and Vigoro 61R36 (CS2), Vigoro Seeds, Galesburg, IL] grown on adjacent fields. The forages were harvested at approximately 39% DM, chopped to a length of about 1.5 cm using a Claas Jaguar 850 forage harvester (Claas of America, Columbus, IN), and dumped in separate 500-kg piles. Representative 70-kg subsamples were taken from each pile and spread on separate tarpaulin sheets. The subsample of forage on each tarpaulin sheet was sprayed, with constant manual mixing, with 154 mL of either distilled water (control) or Pioneer 11CFT inoculant solution (Pioneer Hi-Bred, A DuPont Business, Johnston, IA). The inoculant was applied at the recommended rate of 2 mL/kg to supply 1.0 x 104 cfu/g of Lactobacillus casei strain PTA6135 and 1.0 x 105 cfu/g of Lactobacillus buchneri strain PTA6138. Subsequently, four 10-kg subsamples of treated forage from each tarpaulin sheet were weighed into plastic bags within 20-L plastic mini silos at an approximate packing density of 230 kg/m3 (DM basis). The bags were sealed with plastic ties, and the mini silos were covered, weighed, and held in an enclosed barn at ambient temperature (25 to 30°C) for 110 d. In addition, three 0.5-kg representative forage samples taken from each tarpaulin sheet after inoculant application and mixing were stored on ice and later (about 1.5 h) frozen (–20°C) for subsequent chemical analysis. At 110 d after ensiling, each mini silo was weighed and opened, and a representative subsample was obtained for chemical and fermentation product analysis (1 kg), in situ degradability analysis (3 kg), microbial enumeration (1 kg), aerobic stability (1 kg), and storage at –20°C. Silage samples destined for microbial analysis were heat-sealed within gas-impermeable bags (Kapak/ Scotch Pak, Kapak Corp., Minneapolis, MN) and immediately dispatched on ice to ABC Research Corp. (Gainesville, FL) for enumeration of lactic acid bacteria and to Dairyland Laboratories Inc. (Sauk Rapids, MN) for counting of yeasts and molds. Samples reserved for analysis of silage fermentation products and chemical composition were sent to Dairyland Laboratories for analysis of VFA, NH3-N, pH, DM, CP, ash, NDF, ADF, and water-soluble carbohydrates (WSC).
In Situ Trial
Care of animals used in this study followed protocols approved by the University of Florida Institutional Animal Care and Use Committee. Forage samples from each mini silo were dried at 60°C for 48 h, ground through a 6-mm screen in a Wiley mill (A. H. Thomas, Philadelphia, PA), and sextuplicate samples were weighed (1.8 g) into in situ 5.5 x 5.5 cm, 40 ± 15 µm Dacron bags(Ankom Technology, Macedon, NY). Bags were incubated for 0, 4, 8, 16, 24, or 48 h in each of 2 lactating rumen-fistulated dairy cows given ad libitum access to a ration consisting of 49% corn silage, 14% alfalfa hay, and 37% concentrate (DM basis). At each incubation period, 6 replicates per mini silo (2 cows x 3 replicates/cow) were incubated. After incubation, bags were washed in a washing machine (Kenmore Series 70, Sears, Roebuck & Co., Hoffman Estates, IL) using a cool rinse cycle, dried at 60°C for 48 h, and weighed; DMD was then calculated. Contents of bags incubated for 24 and 48 h were composited by cow and incubation period, ground through a 1-mm screen with a cyclone mill (3010-030, Udy Corp., Fort Collins, CO), and analyzed for DM and NDF concentration; 24-h and 48-h DMD and NDFD were calculated.
Laboratory Analysis
Oven DM concentration was determined in a forced-draft oven at 60°C for 48 h. Crude protein was calculated as N x 6.25; N was measured using a modification of the Kjeldahl procedure described by Noel and Hambleton (1976) that includes colorimetric N quantification rather than distillation. Ash content was determined as residue remaining after samples were placed in a muffle furnace at 550°C for 5 h. Concentrations of NDF and ADF were determined (Van Soest et al., 1991) using an Ankom200 Fiber Analyzer (Ankom Technology). Water-soluble carbohydrate concentration was colorimetrically determined after acid hydrolysis (Hall et al., 1999). Silage fluid was extracted by blending 15 g of silage in 200 mL of distilled water for 2 min. The pH was measured using a pH meter (Orion 410A, Allometrics Inc., Baton Rouge, LA). The filtrate was centrifuged at 4°C and 21,500 x g for 20 min; lactate, 1,2 propanediol, VFA, and ethanol were measured in the supernatant fluid using the method of Muck and Dickerson (1988) and a high-performance liquid chromatograph (L7485, Hitachi, Tokyo, Japan) fitted with a UV detector (Spectroflow 757, ABI Analytical Kratos Division, Ramsey, NJ).
Yeasts and molds were enumerated by pour-plating in standard methods (M124) agar, to which 40 mg/ kg of chloramphenicol and chlortetracycline were added (Tournas et al., 1998). Plates were incubated aerobically at 25°C for 5 d. Lactic acid bacteria were enumerated by pour-plating in Elliker agar using the method of Downes and Ito (2001). Aerobic stability was measured by placing thermocouple wires at the center of a bag containing 800 g of silage within an open-top polystyrene box that was covered with 2 layers of cheesecloth to prevent drying of the silages. The thermocouple wires were connected to data loggers (Campbell Scientific Inc., North Logan, UT) that recorded the temperature every 30 min for 30 d. Aerobic stability was denoted as the time (h) interval before silage temperatures increased by 2°C above ambient temperature (23 to 27°C).
Statistical Analysis
The data for each corn silage were separately analyzed; data were from concurrent experiments with completely randomized designs. Chemical and microbial data from both experiments were analyzed with the GLM procedure (SAS Institute, 2002). The model included effect of the inoculant. In situ rumen degradation data were fitted to the model of McDonald (1981) with the resulting parameters analyzed using the NLIN and GLM procedures (SAS Institute, 2002), respectively. Statistical significance was declared at the 5% level with trends being noted at the 6 to 10% significance level.
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RESULTS AND DISCUSSION
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Chemical Composition of Pre-Ensiled Corn Forages
The chemical composition of the freshly treated corn forages before ensiling is shown in Table 1
. Inoculant application did not affect chemical composition although a slight difference (P = 0.004) in the DM concentration of control and inoculated CS1 samples was evident. The chemical compositions of both hybrids were within the expected range for corn grown in Florida (Arriola et al., 2005; Kim and Adesogan, 2006).
Chemical Composition of Corn Silage
Inoculated CS1 silages tended to have greater (P = 0.055) DM and lesser ash (P = 0.053) concentrations versus the controls; otherwise, inoculant application did not affect (P > 0.1) the chemical composition of either silage (Table 2). Compared with CS1, CS2 had slightly greater CP, ash, NDF, and ADF concentrations and lesser WSC concentration, reflecting differences between the hybrids or in their growth environments. Differences between pre-ensiled and ensiled NDF concentrations of these silages suggest that greater cell-wall hydrolysis had occurred during fermentation of CS1 (loss of 6.7 vs. 1.8 percentage points in NDF due primarily to loss of 7.5 vs. 0.8 percentage points in hemicellulose for CS1 and CS2, respectively).
Fermentation Characteristics of Corn Silage
Silage pH was unaffected (P > 0.1) by inoculation (Table 3) and the low pH values achieved indicated that all silages had fermented adequately. Inoculation did not affect (P > 0.1) the concentration of NH3-N (% of DM) of CS1 but decreased (P = 0.004) that of CS2. Unlike in CS2, inoculation of CS1 decreased (P < 0.01) concentrations of total fermentation acids and lactate as well as lactate to acetate ratio and increased (P < 0.05) concentrations of ethanol and propionate. Epiphytic microorganisms such as Lactobacillus diolivorans can convert the 1,2 propanediol formed during lactate degradation by L. buchneri into propionate (Oude Elferink et al., 2001; Krooneman et al., 2002). However, their role in increasing the propionate concentration in this study is not conclusive because 1,2 propanediol concentration was unaffected by inoculation. The absence of an acetate response to inoculation is noteworthy because L. buchneri inoculants typically increase aerobic stability by increasing acetate concentration and thereby inhibiting the growth of spoilage-initiating molds (Driehuis et al., 1999; Ranjit and Kung, 2000; Kleinschmit et al., 2005). Lactobacillus buchneri-related increases in acetate concentration have been less pronounced in a few studies with dual-purpose inoculants that contain a mixture of active homolactic bacteria and L. buchneri (Filya, 2003; Adesogan et al., 2004). A review of the effects of applying dual-purpose inoculants to forages revealed that acetate concentration was increased about 69% of the time, not affected about 25% of the time, and decreased about 6% of the time (Adesogan, 2008). Because greater rates of inoculation have been more effective (Kleinschmit and Kung, 2006), application of 105 cfu/g of L. buchneri in this study may explain why inoculation did not increase the concentration of lactate degradation products such as acetate, 1,2 propanediol, and ethanol. The fact that inoculation did not affect the fermentation acid concentration of CS2 forage may partly reflect its lesser WSC concentration.
Dual-purpose inoculants typically contain heterolactic L. buchneri bacteria to improve aerobic stability and homolactic bacteria to prevent the small increases in DM losses and pH that typically result when L. buchneri alone is applied to forages (Kleinschmit and Kung, 2006). The presence of L. casei in the dual-purpose inoculant used in this study appears to be justified because pH and DM losses were not increased by inoculation.
Microbial Counts and Aerobic Stability of Corn Silage
Inoculation tended (P = 0.082) to reduce yeast counts and increase (P = 0.001) aerobic stability of CS1 by 57.3 h (98%; Table 4). In contrast, inoculated CS2 silages had greater (P = 0.003) yeast counts, tended to have greater mold counts (P = 0.067), and were 20% less (P = 0.035) aerobically stable than the corresponding control silages. The aerobic stability data reflected differences in counts of yeasts, which usually initiate aerobic deterioration of silages (Higginbotham et al., 1998). The inoculant-induced improvement in aerobic stability of CS1 may be attributable at least partly to the increase in propionic acid concentration. Increased stability of L. buchneri-treated corn silage is consistent with other reports and is attributable to increases in concentrations of acetate or propionate, or both (Ranjit and Kung, 2000; Krooneman et al., 2002; Filya, 2003). The reason why inoculation had different effects on fungal counts and stability of the silages is unknown.
In Situ Degradation
Inoculation increased (P = 0.027) the potentially degradable fraction of CS1 and increased (P < 0.05) the total degradable fraction, 24-h DMD, 48-h DMD, and 48-h NDFD of CS2 (Table 5). Therefore, the inoculant was less successful at increasing the DMD and NDFD of CS1. The reason for this difference is unclear but it may reflect differences in lignin concentration. The 11% increase in 48-h NDFD of CS2 in this study is greater than that reported for corn silage (7%) and at the upper range of that for ryegrass silage (9 to 11%) treated with ferulic acid esterase-producing L. buchneri (Nsereko et al., 2006a). Ferulic acid esterase releases ferulic acid from cell-wall arabinoxylans and may thereby directly increase fiber digestion or increase the susceptibility of the cell wall to further cellulolytic or xylanatic hydrolysis. Several recent studies have demonstrated that addition of esterase to xylanase and cellulase enzyme mixtures increases in vitro forage fiber digestion (Eun and Beauchemin, 2006; Krueger and Adesogan, 2008; Krueger et al., 2008).
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Table 5. Effect of inoculant1 application on kinetics of in situ ruminal DM degradability and 24-h and 48-h DM and NDF degradability (%) of 2 corn silages
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In general, this study reveals that effects of inoculation differed with the silage for unknown reasons. Factors that may have contributed to the different effects include differences in epiphytic bacterial population, water activity, WSC concentration, and cell-wall component concentrations (McDonald et al., 1991).
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CONCLUSIONS
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Inoculation reduced the lactate to acetate ratio and increased propionate concentration, aerobic stability, and total degradable fraction of one corn silage. Inoculation also increased the potentially degradable DM fraction, 24-h and 48-h DMD, and 48-h NDFD of the other silage, but also increased yeast counts and decreased the aerobic stability of the second silage. Future studies should investigate the effects of this inoculant on other corn silages and on feed intake and milk production by dairy cows.
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ACKNOWLEDGEMENTS
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This study was funded by Pioneer Hi-Bred, a Du-Pont Business (Johnston, IA). The authors gratefully acknowledge the assistantship to T. W. Kang provided by Brain Korea 21, Gyeongsang National University, South Korea.
Received for publication October 15, 2007.
Accepted for publication August 1, 2008.
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ABSTRACT
INTRODUCTION
