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Published online 24 January 2006
Published in Crop Sci 46:337-344 (2006)
© 2006 Crop Science Society of America
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FORAGE & GRAZINGLANDS

Effects of Forage Length and Bale Chamber Pressure on Pearl Millet Silage

K. J. Han*,a, M. Collinsb, M. C. Newmanc and C. T. Doughertyd

a Forage Improvement Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, OK 73401
b Dep. of Plant and Soil Sciences, Mississippi State University, 117 Dorman Hall, Box 9555, Mississippi State, MS 39762
c Dep. of Animal Sciences, Univ. of Kentucky, Lexington, KY
d Dep. of Plant and Soil Sciences, 500 S. Limestone St., Univ. of Kentucky, Agric. Science Center- North, Lexington, KY 40546-0091.40546

* Corresponding author (kjhan{at}noble.org)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULT AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Pearl millet [Pennisetum americanum (L.) Leeke] is an annual warm season (C4) grass that has a high yield potential during summers when cool season species are heat-stressed and unproductive. In two field trials, 650 kg round bales were made from long (>100 cm) or short (chopped) ({approx}15 cm) forage and at bale chamber pressures of 421 or 842 x 103 Pa. After 24 h of wilting, forage moisture concentrations at Trial 1 and Trial 2 were 771 and 583 g kg–1, respectively. The higher baling pressure increased both mass and density of bales (P < 0.05). Length of cut had no effect on bale weight or density. Core temperatures were lower in higher density bales when the concentration of forage moisture was lower. Water-soluble carbohydrate concentrations were lower in silages made from the shorter forages (P = 0.013). Nutritive value of silage decreased during 8 mo of storage regardless of treatment. Baling chamber pressure and forage chopping treatments did not affect neutral detergent fiber (NDF) or in vitro dry matter digestibility (IVDMD) of post-storage silage. Acidity of silage ranged from pH 4.13 to 5.31. Lactic acid concentrations were lowest in silage in Trial 1 made from the wetter forage (771 g kg–1) when chopped to 100 cm. Listeria was present in bales made from the wetter forage. Clostridium botulinum was detected in silage made from chopped forage when baled at low chamber pressure.

Abbreviations: WSC, water soluble carbohydrate • CP, crude protein • DM, dry matter • IVDMD, in vitro dry matter digestibility • NDF, neutral detergent fiber • VFA, volatile fatty acids


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULT AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
PEARL MILLET is an annual warm-season (C4) species with annual dry matter (DM) yields ranging from 3.6 to 8.1 Mg ha–1 (Maiti and Wesche-Ebeling, 1997). Pearl millet is more tolerant of low soil fertility and drought, and often has higher crude protein (CP) concentrations, than sorghum [Sorghum bicolor (L.) Moench] or corn (Zea mays L.) (Pearson, 1985; Ojeda et al., 1990; Woodruff et al., 1995). In cattle feeding trials, DM intake of pearl millet silage may be equal to or superior to DM intake of maize silage (Miaki et al., 1990; Ward et al., 2001).

Pearl millet may be inferior in nutritive value to sorghum or maize as a silage crop because grain accounts for only 12% of whole crop DM (Hattendorf et al., 1988; Ward et al., 2001) and because of low concentrations of water soluble carbohydrate (WSC). The rate of conversion of starch to soluble carbohydrates is also an important factor influencing the rate and totality of fermentation of forage crops (Wilson and Collins, 1980). Consequently, pearl millet silage may have higher final pH than sorghum silage or maize silage (Miaki et al., 1990; Hill et al., 1999; Ward et al., 2001).

Preservation of forage as silage in round bales may use existing haymaking equipment and minimize investment in silage infrastructure as well as reduce field losses of nutrients. In the UK, regulations on silage effluent management have also encouraged conservation of forages as baled silage (Sargison, 1993).

Silage in large bales usually has lower DM density than chopped, well-consolidated forage in conventional silos and may have more aerobic spoilage as a consequence (Givens et al., 1993). Forage DM concentrations above 500 g kg–1 are usually associated with lower DM density, in contrast bulk density peaks around 350 g kg–1 DM (Rohner and Wyss, 1995). McGechan (1990) found that reducing forage particle size from 100 to 20 mm increased DM density by 20%. Shinners et al. (1994) reported 16% increase in DM density when particle size decreased from 25 to 9 mm. Marsh (1978) observed that reducing particle size increased concentrations of fermentation products and lowered silage pH. Charmley et al. (1999) observed that macerating forage before baling improved feed conversion rate of round bale silage. Wilting and processing of forage before baling, thus may be used to manipulate fermentation of round bale silage.

Animals ingesting silage in round bales may be exposed to listeriosis, botulism, and abortifacients (Ricketts et al., 1984; Fenlon, 1985; Fenlon et al., 1989; Sargison, 1993; Ruxton and Gibson, 1995; Skaar and Stenwig, 1996), especially in silage made during cool weather when suboptimal populations of homo-fermentative lactobacilli may achieve only partial fermentation. The incidence of Listeria monocytogenes in moldy, bale silage was 44% (Fenlon, 1985). Round bale silage spoiled by aerobic deterioration may harbor Listeria. Ricketts et al. (1984) associated death and illnesses of livestock with the presence of C. botulinum in baled silage. Roberts (1988) reported that pH, temperature, and water activity of silages affected populations of C. botulinum.

The objective of these studies were to determine if processing of forage before baling and increasing bale density could improve forage quality and fermentation characteristics and lower pathogenicity of round bale silage.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULT AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
This study was conducted at the University of Kentucky Spindletop Farm, near Lexington, KY (38°8' N; 84°31' W). ‘Millex 32’ pearl millet was drilled in rows 17.8-cm rows on 15 May 2001 at a rate of 20 kg pure live seeds ha–1 on a Maury silt loam soil (Typic Paleudalfs). Nitrogen, applied as ammonium nitrate, was broadcast at 168 kg ha–1 of N at planting. Forage was cut to a 10-cm stubble height with a sickle-bar mower-conditioner at early bloom (31 July 2001, Trial 1) and again on 30 Sept. 2001(Trial 2). Crop height at the time of harvest was approximately 185 cm for Trial 1 and 110 cm for Trial 2. Pearl millet forage was mowed, conditioned, and wilted more than 24 h before baling.

Bales (1.5 x 1.2 m in length) were made with a New Holland model 648 baler (New Holland North America, Inc., New Holland, PA). Forage was baled directly (185 cm in Trial 1, 110 cm in Trial 2) or chopped to 15 cm during the baling operation. Dry matter density treatments were achieved by setting bale chamber pressures at 421 or 842 x 103 Pa.

Randomly selected windrows were used to make 12 bales for each treatment of Trial 1 and six bales for each treatment of Trial 2. Two core samples were taken from each short axes to center of the bales with a 50-mm i.d. x 1.2-m sampling probe with a serrated cutting tip. The sampling cavities were plugged with paper towels. One-half of each core sample was freeze-dried for determination of WSC concentration and the rest was dried at 60°C for 72 h for the estimation of DM concentration and feed value. Dried samples were milled through a 2-mm screen and then again through a 1-mm screen.

Silage bales were wrapped within 4 h after baling with four layers of 76 cm wide stretch film (Sunfilm, AEP Industries, Inc., South Hackensack, NJ) with a New Holland B27P bale wrapper (New Holland North America, Inc., New Holland, PA). Bales were weighed after wrapping. Bale diameters were measured at 0 to 6 h and 3 to 9 h on both round faces and bale length was determined. Thermocouples (copper-constantan) were inserted in the center of bales from a round face end and core temperatures read at 1300 h everyday until temperatures had stabilized.

After 8 mo of storage on grass sod, film wraps were removed from the bales and weights, diameters, and lengths of bales were retaken. Core samples of silage were handled and processed as before. Silage samples for microbial analysis were taken from the bottom 30 cm of bales and transferred to microbiology laboratory for immediate analysis.

WSC was determined from acidic methanol extract of freeze-dried silage samples (Harvey et al., 1969). NDF was determined with an ANKOM Model 200 fiber analyzer (ANKOM Technology, Macedon, NY) using the sodium sulfite modification of Robertson and Van Soest (1981). Total nitrogen was measured using a semimicro-Kjeldahl procedure of Bremner and Breitenbeck (1983) and CP was calculated as N x 6.25. Duplicate 0.25-g samples were used to determine IVDMD by the method of Goering and Van Soest (1970).

Wet silage was homogenized for 30 s in distilled water (10:1 w/w). Silage pH was measured on the homogenate after filtering through four layers of cheesecloth. Aliquots of 1-mL filtrate were mixed with 0.2 mL of 25% (v/v) metaphophoric acid and centrifuged at 5°C at 21 600 g for 20 min. Volatile fatty acids in the supernatant were determined by gas chromatography (PerkinElmer Inc., Foster City, CA) as described by Baumgardt (1964) and Brotz and Schaefer (1986). Lactate concentrations were determined by an enzymatic method (Hohorst, 1963) using DL-lactic acid lithium salt (Sigma-Aldrich, St. Louis, MO).

Isolation media and identification methods were as described by Bacteriological Analytical Manual (U.S. Food & Drug Administration, 2001). For detection of mold and yeast, 25-g silage samples were diluted with 225 mL of peptone solution (pH 7.4) and stomached for 60 s. Serial dilutions were plated on Czapek-Dox (Difco, Becton Dickinson and Company, Franklin Lakes, NJ) agar and incubated at 26°C for 5 d. For Trial 1, Listeria spp. were counted on Modified Oxford agar (MOX; Difco, Becton Dickinson and Company, Franklin Lakes, NJ) after 48 h of incubation at 35°C.

In Trial 2, approximately 25 g of each silage sample was stomached in 225 mL of UVM-modified Listeria enrichment broth (Difco; pH 7.2) for 60 s and transferred into tubes for incubation at 35°C for 24 h. The extract was also transferred to Fraser Listeria Enrichment Broth Base (Difco) and incubated for 24 to 48 h. After incubation, the enrichment was streaked onto MOX plates then incubated at 36°C for 24 h. Primary detection of Listeria spp. was based on the number of black colonies on the plates. Colonies from presumptive positive plates were transferred to tubes containing Brain Heart Infusion (BHI; Difco) and incubated for 24 h. Cultured cells were then gram-stained and biochemical tests were performed to confirm the isolates as Listeria spp.

For the determination of Clostridium spp., 1 g of silage was incubated at 35°C in chopped meat broth (Difco) for 48 h. Cultured cells were streaked on Shahidi-Ferguson Perfringens agar (SFP agar) plates (Difco) and incubated anaerobically 24 h at 35°C. Black colonies were selected and evaluated for motility and nitrate reduction. The presence of gram-positive, spore-forming rods that were gelatin-positive and nitrate-positive were considered presumptive positive for Clostridium spp. in Trial 1. In Trial 2 Clostridium spp. were identified with the aid of an API-20A kit (bioMerieux, Durham, NC).

Pre-and post-storage silage data were analyzed by the mixed model procedure (Littell et al., 1996) of SAS (SAS Inst., 2001). Data were analyzed as a completely randomized design with 12 (Trial 1) or six (Trial 2) replicates of a 2 x 2 factorial of bale chamber pressure and forage length. Bale chamber pressure and forage length were considered fixed effects and trial was treated as a random effect. Bale temperature data were analyzed by repeated measures analysis of variance procedures of SAS with date as the repeated factor. The autoregressive order 1 covariance structure was used in the repeated measures analysis. A pairwise t test was used for means comparison. Statistical significance is at the 0.05 level, unless otherwise stated.


   RESULT AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULT AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Properties of Wilted Forage
One full day of wilting reduced moisture concentration of pearl millet to 771 and 583 g kg–1 in Trial 1 and 2, respectively (Table 1). In Trial 1, concentrations of CP and WSC within pearl millet forage were 21 g kg–1 DM and 54 g kg–1 DM higher than respective concentration of CP and WSC in Trial 2. Wilted forage from Trial 1 had higher NDF (43 g kg–1 DM) and slightly lower IVDMD (17 g kg–1 DM) than the drier forages of Trial 2. The availability of substrates for fermentation of wilted forage was adequate for the production of high quality silage. First harvest pearl millet forage required more swath manipulation and longer wilting time for the production of baled silage than second growth because of greater biomass.


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  		Table 1. Moisture, water soluble carbohydrate (WSC), crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF), and in vitro dry mater digestibility (IVDMD), of wilted pearl millet in Trials 1 and 2.

 
Interactions and Properties of Silage Bales
Significant interactions for Trial (T) x chamber pressure (C) for bale weight, DM bale weight, and DM density (Table 2) indicated interactions between forage moisture content and bale chamber pressure. Increasing bale chamber pressure from 421 to 842 x103 Pa raised bale density by 60% (52 kg DM m–3) in Trial 1 and by 33% (47 kg DM m–3) in Trial 2 (Table 3). The effect of chamber pressure on bale properties was less when silage was made from drier forage. Other T x C interactions for pH (Table 4), lactic, propionic, isobutyric, butyric, and isovaleric acids (Table 5) reflect the effect of forage moisture content and bale physical properties on fermentation, possibly related to differences in air entrapment. Significant interactions for T x C x forage length (L) for WSC (P < 0.05) and propionic acid concentrations (P < 0.05) (Table 4 and 5) indicated that chopping promoted fermentation.


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  		Table 2. Significance of trials x treatment interactions for moisture concentration, bale weight, dry bale weight, and dry matter recovery of pearl millet round bale silage.

 

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  		Table 3. Influence of bale chamber pressure (High: 842 vs. Low: 421 x 103 Pa) and forage length (Long: ≥ 110 cm vs. Short: {approx}15 cm) on post storage bale characteristics of pearl millet round bale silage in Trials 1 and 2.

 

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  		Table 4. Significance of trials x treatment interactions for pH, water soluble carbohydrate (WSC), crude protein (CP), neutral detergent fiber (NDF), and in vitro dry mater digestibility (IVDMD) of pearl millet round bale silage.

 

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  		Table 5. Significance of trials x treatment interactions for lactic acid and volatile fatty acid (VFA) of pearl millet round bale silage.

 
Huhnke et al. (1997) noted that high quality silage resulted when forage was baled at <500 g kg–1 moisture. These researchers suggested that ensiling low moisture forage prevented deformation of silage bales and helped maintain the integrity of the plastic wrap. Although there were no significant treatment differences in bale dimensions during storage in Trial 1, bale height and bale length decreased 8.8 and 6.3 cm, respectively (SE = 1.43 and 1.42). In Trial 2, bale height declined by 6.29 cm and bale length increased by 1.9 cm. Baling wilted pearl millet forage near 550 g kg–1 moisture produced uniform round bales that retained shape during storage.

Silage density varies widely (Givens et al., 1993; Shinners et al., 1994; Rohner and Wyss, 1995). Ruppel et al. (1995) suggested 225 kg m–3 as a minimum bulk density for silage in bunker silos. Muck and Holmes (1998) reported that bulk density and forage length affected the amount of air inclusion in silage. In our trial, chopping long forage (80–100 cm) to 15-cm lengths did not increase bulk density.

Dry matter recovery, based on the difference of pre- and post-storage DM mass, varied with treatment in Trial 1 but not in Trial 2 (Table 3). In properly sealed bales of silage, fermentation products are retained in solution or in headspace; Pitt (1990) estimated stoichiometrically that 60% of the mass of respired carbohydrate was retained in the silage as water.

Bale temperature during the storage period increased rapidly during the first 3 d of ensiling then declined slowly to ambient temperature within 3 wk (Fig. 1 and 2) . Treatments did not affect maximum bale temperatures in Trial 1 (Table 3). In Trial 2, however, the peak temperatures reached in bales made at the lower chamber pressure were higher than peak temperatures of bales made at the higher pressure. Although moisture concentration of the ensiled forage was lower in Trial 2 than in Trial 1, bale temperatures were much higher in Trial 1 than Trial 2. In the latter trial, when pearl millet was baled at 400 g kg–1 DM at lower ambient air temperatures, there was no significant heating. Rotz and Muck (1994) observed the Maillard reaction in bunker silos when core temperatures were above 35°C, apparently because of slow heat dissipation. The high surface area to weight ratio of round bales appears to facilitate heat dissipation and relieve heat accumulation compared with larger silage units. In Trial 2, bale temperatures reached a peak of 31°C within 3 d, but these temperatures were not sustained for more than 24 h. Furthermore, heat-generating aerobic degradation may have been gradually suppressed by the progressive development of anaerobic conditions. Properly wilted and well-packed round bale silage may have less spoilage and heat-generated degradation than conventional forage silage systems.


Figure 1
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  		Fig. 1. Bale temperature change of pearl millet round bale silages (HS: high chamber pressure {approx} 842 x 103 Pa and short forage length {approx} 15 cm, HL: high chamber pressure {approx} 842 x 103 Pa and long forage length {approx} 185 cm, LS: low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm, and LL: low chamber pressure {approx} 421 x 103 Pa and long forage length {approx} 185 cm) in Trial 1.

 

Figure 2
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  		Fig. 2. Bale temperature change of pearl millet round bale silages (HS: high chamber pressure {approx} 842 x 103 Pa and short forage length {approx} 15 cm, HL: high chamber pressure {approx} 842 x 103 Pa and long forage length {approx} 110 cm, LS: low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm, and LL: low chamber pressure {approx} 421 x 103 Pa and long forage length {approx} 110 cm) in Trial 2.

 
The t tests for the parameters of temperature models were all significant in Trial 1 (Table 6). The starting temperatures (y intercepts) of bales were similar for treatments. The linear coefficients for day variables were negative for all treatment with slopes ranged from –1.53 to –0.87. However, the coefficients of quadratic effects of day were positive with a small slope indicating slower temperature declines over days. In Trial 2, the models of bale temperatures of HL (842 x 103 Pa and long forage length {approx} 110 cm) and LS (low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm) had similar linear and quadratic coefficients to each other. The LL treatment (bale chamber pressure {approx} 421 x 103 Pa and {approx} 110 cm long forage) indicated a significant linear trend with time day effect (p < 0.001).


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  		Table 6. Regression analyses for bale temperature of pearl millet round bale silages in Trial 1 (HL: high chamber pressure {approx} 842 x 103 Pa and long forage length {approx} 185 cm, HS: high chamber pressure {approx} 842 x 103 Pa and short forage length {approx} 15 cm, LL: low chamber pressure {approx} 421 x 103 Pa and long forage length {approx} 185 cm, and LS: low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm) and Trial 2 (HL: high chamber pressure {approx} 842 x 103 Pa and long forage length {approx} 110 cm, HS: high chamber pressure {approx} 842 x 103 Pa and short forage length {approx} 15 cm, LL: low chamber pressure {approx} 421 x 103 Pa and long forage length {approx} 110 cm, and LS: low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm).

 
Chemical Composition and Digestibility of Post-Storage Silage
Chopping pearl millet forage before baling lowered post-storage WSC compared with silage produced from unchopped forage in both trials (P < 0.05; Table 7). Chopping may have facilitated the conversion of starch to WSC and promoted fermentation. The presence of appreciable levels of WSC in silage after storage may indicate that WSC was not limiting fermentation in our trials. In Trial 2, only CP increased with bale density (P < 0.01). Although the NDF in post-storage silage was higher than that pearl millet forage, NDF values were not affected by bale density and chopping treatments regardless of moisture concentration of pearl millet.


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  		Table 7. Influence of bale chamber pressure (High: 842 vs. Low: 421 x 103 Pa) and forage length (Long: ≥ 110 cm vs. Short: {approx}15 cm) on post-storage water soluble carbohydrate (WSC), crude protein (CP), neutral detergent fiber (NDF), and in vitro dry mater digestibility (IVDMD) of pearl millet round bale silage in Trials 1 and 2 (g kg–1 DM).

 
Fermentation Products
The pH of pearl millet silage was significantly lowered by increasing bale density in Trial 1 but not in Trial 2 (Table 8). Hill et al. (1999) reported that pH of chopped pearl millet silage ranged from 4.12 to 6.04. McCullough (1978) suggested that pH 4.2 could be used as a benchmark for well-preserved silage, and Edwards and McDonald (1978) found more putrefaction of silage when pH was above 4.2 and moisture concentration was above 820 g kg–1. Although pH of silages from Trial 1 was above 4.2, fermentation was satisfactory because lactic acid accounted for most of the VFAs and because butyric acid concentrations were low (Table 8). Pearl millet silage had higher concentrations of lactic acid when the source forage was chopped into smaller particles (Trial 1), but this was not reflected in bale pH. The differential moisture content of forages accounts for the difference in silage pH between the two harvests. Charmley and Firth (2004) reported more complete fermentation in silos filled with flail cut unwilted forage (163 g kg–1 DM) than in baled silage made from wilted (468 g kg–1 DM) forage. They also indicated that fermentation of flail cut forage stored in silos was less affected by low forage DM than that ensiled in bales. Our trials indicate that higher forage DM concentration is desirable when it is preserved in round bales. Moisture control in forage before baling seems to be even more important than additives or particle size in the production of high quality silage. From comparisons of pearl millet, sorghum, or corn silage, Hill et al. (1999) and Ward et al. (2001) concluded that pearl millet was a weak candidate for high quality silage because of low WSC content of source forage. Our trials, in contrast, show that wilted, drier pearl-millet forage (Trial 2) may be preserved as lactic acid-stabilized silage in large round bales without severe quality degradation. The WSC would not be a limiting factor in fermentation of pearl millet.


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  		Table 8. Influence of bale chamber pressure (High: 842 vs. Low: 421 x 103 Pa) and forage length (Long: ≥110 cm vs. Short: {approx}15 cm) on pH, lactic acid, and volatile fatty acid (VFA) concentration of pearl millet round bale silage in Trials 1 and 2 (g kg–1 DM).

 
Baling pearl millet forage at high chamber pressures increased density and lactic acid concentrations in silage especially that made from high moisture forage. Pauly and Lingvall (1999) reported that increasing bale density from 107 to 182 kg DM m–3 increased lactic acid production and decreased silage pH in timothy (Phleum pratense L.)–meadow fescue (Lolium pratensis Huds) silage. High concentrations of lactic acid and low concentrations of propionic acid and butyric acid indicate that homofermentation was favored by higher bale density. The lactic acid to acetic acid ratio averaged 3.06 and 8.40 in Trials 1 and 2, respectively. Charmley et al. (1999) reported lactic acid to acetic acid ratios of 5.7 and 8.7 for conditioned and macerated round bale silages, respectively. Silage at Trial 2 showed no significant difference in concentrations of lactic acid and acetic acids among treatments. Isobutyric acid was not detected and low concentrations of butyric acid were detected in Trial 2 (Table 8). Ward et al. (2001) reported higher concentrations of isobutyric acid than n-butyric acid when proteolytic clostridia were dominant. If this relationship holds, then pearl millet silage made in our trials should have limited proteolysis from clostridial activity. Although treatment effects were not found for pH and fermentation products measured in Trial 2, high concentrations of lactic acid and low concentrations of butyric acid indicated forage quality of pearl millet might be maintained in round bale silage for at least 8 mo.

Microbial Analyses
Microbial analyses were conducted on pearl millet balage from Trial 1. Bale deformation during storage may break the stretch film seals and invite air infiltration and aerobic deterioration leading to degradation of lactic acid and reduction in acidity. Deformed bales typically were made from forage with more than 800 g kg–1 moisture. Mold counts for pearl millet silage from Trial 1 (Table 9) were similar to the range of 8.9 to 9.3 x 105 CFU reported by Skaar and Stenwig (1996) for grass silage bales. Assays using selective media revealed the presence of Listeria spp. in bales made from low density, long forage baled silage; however, the catalase assay confirmed the presence of Listeria in only one bale.


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  		Table 9. Summary of microbial analyses of pearl millet round bale silages (HL: high chamber pressure {approx} 842 x 103 Pa and long forage length {approx} 185 cm, HS: high chamber pressure {approx} 842 x 103 Pa and short forage length {approx} 15 cm, LL: low chamber pressure {approx} 421 x 103 Pa and long forage length {approx} 185 cm, and LS: low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm) in Trial 1.

 
In Trial 2, assay of silage from one bale made at low chamber pressure and unchopped forage and one bale made at low chamber pressure and from chopped forage indicated the presence of C. botulinum (Table 10). These bales of silage had pH above 4.5. Listeria spp. were not detected in pH 4.2 silage made from high DM forage. In that trial, bales were better formed and retained their cylindrical shape and had better seals between overlapping stretch films. Ricketts et al. (1984) reported clostridial growth in silages at pH 4.5 and 850 g kg–1 moisture. The detection of several species of Clostridium in high pH silage may indicate potential pathogenicity.


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  		Table 10. Summary of microbial analyses of pearl millet round bale silages (HL: high chamber pressure {approx} 842 x 103 Pa and long forage length {approx} 110 cm, HS: high chamber pressure {approx} 842 x 103 Pa and short forage length {approx} 15 cm, LL: low chamber pressure {approx} 421 x 103 Pa and long forage length {approx} 110 cm, and LS: low chamber pressure {approx} 421 x 103 Pa and short forage length {approx} 15 cm) in Trial 2.

 

   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULT AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
Storing pearl millet as round bale silage is a feasible method of forage preservation. High yields, low dry matter content, and slow drying conditions, as may be experienced during the first harvest, may require more than 24 h of wilting. Raising bale chamber pressures may promote favorable conditions for fermentation of pearl millet when the forage moisture concentration is in the range of 550 to 750 g kg–1. Chopping forage may enhance fermentation by accelerating the release of substrates. Pathogenic organisms, such as Listeria spp. and C. botulinum, may grow in silages made from high moisture forages or in deformed bales when air penetrates broken, shrink wrap seals.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULT AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Supported in part by USDA CSREES grant funds. Published with the approval of the Director, KY Agric. Exp. Stn. as publication 05-06-020.

Received for publication February 22, 2005.


   REFERENCES
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULT AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 





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