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Published online 1 February 2006
Published in Crop Sci 46:688-694 (2006)
© 2006 Crop Science Society of America
677 S. Segoe Rd., Madison, WI 53711 USA
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FORAGE & GRAZINGLANDS

Forage Preservation Method Influences Alfalfa Nutritive Value and Feeding Characteristics

D.W. Hancock*,a and M. Collinsb

a Dep. of Biosystems and Agricultural Engineering, 119 C.E. Barnhart Building, Univ. of Kentucky, Lexington, KY 40546
b Dep. of Plant and Soil Sciences, 113 Dorman Hall, Mississippi State, MS 39762

* Corresponding author (dhancock{at}bae.uky.edu)


   ABSTRACT
TOP
 NOTES
 ABSTRACT
INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Forage preserved as baled silage can reduce dry matter and quality losses compared with hay systems if sufficient stretch wrap is layered to adequately exclude oxygen. The objectives of this study were to determine the optimum film amount for alfalfa (Medicago sativa L.) preserved as round bale silage and to compare the forage quality and losses to that of dry hay. Two field trials compared alfalfa silages wrapped in two, four, or six layers of plastic film and hay controls. Bales wrapped with four or six layers had significantly lower temperatures than two layer treatments. In Trial 1 (July harvest), silage with two layers had higher post-storage neutral detergent fiber (NDF), acid detergent fiber (ADF), and acid detergent lignin (ADL) concentrations than did silage prepared with either four or six layers. No consistent differences in forage quality parameters were observed among silage treatments in Trial 2 (September harvest). After 5 mo, concentrations of ADF, NDF, and ADL in the silages with four or six layers of film were lower than hay in both trials; however, crude protein (CP) did not differ across preservation treatments. In a preference trial, cows (Bos taurus) offered all treatments from Trial 2 preferred silages preserved with four or six layers of film to the two-layer treatment and hay control. We conclude that more than two layers of film are needed for consistent preservation of alfalfa round bale silage. The results demonstrated the potential advantage in quality for alfalfa baled silage compared with conventionally harvested and stored hay.

Abbreviations: ADF, acid detergent fiber • ADL, acid detergent lignin • CP, crude protein • DM, dry matter • NDF, neutral detergent fiber • NPN, nonprotein nitrogen • TS, total sugars


   INTRODUCTION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
PRESERVING FORAGE CROPS as silage in humid regions can improve DM retention and forage quality compared with hay by reducing field and storage losses. Physical losses to leaf shatter from legume forages can be reduced substantially with silage because moist leaves are less brittle. The rain damage frequently encountered during hay production in these regions (Collins, 1985) is nearly eliminated with silage harvest because of the shorter exposure time needed to wilt forage in the field compared with curing hay (Rotz and Abrams, 1988).

The majority of stored forage in the central and southeastern parts of the USA is presently preserved as round bale hay that typically is stored outside without cover. Equipment and structures needed for production of chopped silage are not widely available in this region, but a system that uses readily available harvest equipment and employs low-density polyethylene plastic stretch film to cover round bales has been developed recently (Robinson et al., 1988; McCormick et al., 1998; Vough and Glick, 1993; Fraser et al., 1999). Round bale silage is prepared by wrapping moist forage in multiple layers of polyethylene stretch film to exclude oxygen and create nearly anaerobic conditions (Redman and Knight, 1992; Lingvall, 1995), providing a suitable environment for growth of silage microorganisms (Honig and Woolford, 1980; Collins and Owens, 2003).

Failure to adequately exclude oxygen in chopped silage systems limits fermentation and can lead to aerobic deterioration, including mold growth, clostridial spoilage, and a decrease in silage palatability (Honig and Woolford, 1980; O'Kiely et al., 1986). Typical plastic films for stretch-wrap silage production are blown or coextruded, low-density polyethylene plastics that are 25.4 µm thick before being stretched 55% or more during application (Cromwell et al., 1994a; Krohn and Jordy, 1997). Their relatively low density of 0.921 g cm–3 causes these polyethylene films to be relatively permeable to oxygen and other gases (Krohn and Jordy, 1997). Cromwell et al. (1994b) found that the oxygen permeability of a single layer of polyethylene film, stretched to 50% of its original length ranged from 0.775 to 0.981 cm3 cm–2 d–1 and varied with film manufacturer. Multiple layers are needed to achieve successful silage preservation (Cromwell et al., 1994b). Producer decisions regarding the optimum amount of film for round bale silage production must balance costs with risks associated with spoilage if anaerobic conditions are not maintained. The primary objective of this work was to determine the optimum amount of film for maximum fermentation with minimum DM and quality losses for alfalfa round bale silage by comparing bale temperatures, deterioration, DM losses, deformation during storage, pre- and post-storage forage quality, silage quality, and animal preference. A secondary objective was to compare the round bale silage and hay forage preservation systems on the basis of DM and forage quality retention and animal preference.


   MATERIALS AND METHODS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Two field trials were conducted. In Trial 1, a 4-ha monoculture of ‘Multistar’ alfalfa on the University of Kentucky Maine Chance Research Farm (84° 29' 16.54'' W long, 38° 6' 13.54'' N lat) was used. Alfalfa was mowed at the mid-bud maturity stage directly into windrows on 7 July 1997 between 1300 and 1500 h with a 2.75-m disc-mower–conditioner (New Idea- Model 5200, AGCO Inc., Atlanta, GA). In Trial 2, a monoculture of ‘Cimarron’ alfalfa grown on a Maury silt loam soil on the University of Kentucky Spindletop Research Farm (84° 29' 40.76'' W long, 38° 7' 15.76'' N lat) was mowed directly into windrows at the mid-bud maturity stage between 1300 and 1500 h on 7 Sept. 1997.

Treatments in Trial 1 consisted of factorial combinations of two levels of moisture at baling, averaging 502 and 373 g kg–1, and two, four, or six layers of plastic film, plus a dry hay control (166 g kg –1 moisture). Swaths were randomly assigned to treatments and four replicates were prepared. Trial 2 was conducted as described for Trial 1 except that the lower-moisture silage treatment was omitted.

Bales for the high-moisture silage treatment were produced the morning after mowing. Bales for low-moisture silage were produced during the afternoon of the day after mowing. Windrows randomly designated for hay production were tedded the morning after they were mowed. Hay production required 3 and 4 d of curing in Trials 1 and 2, respectively. In Trial 2, two rainfall events during the hay-curing period occurred 1 d after baling the silage bales. The first event resulted in 10.9 mm of rain at an average intensity of 1.3 mm h–1 and the second rain deposited 4.3 mm at a rate of 0.9 mm h–1. All bales were formed with a New Holland Model 640 variable-chamber, belt-type round baler (New Holland North America, Inc., New Holland, PA). Ambraco's (American Brazilian Company, Houston, TX) Orangeline 20 000–140 (tensile strength: 965 kPa) and Clearfield 20 000–115 (tensile strength: 793 kPa) plastic twines were used as the binding material for all bales in Trials 1 and 2, respectively. Bale weights were recorded to the nearest 2 kg and one 0.6-m core sample per bale was collected with a hydraulically powered coring tube with serrated tips (2.5 cm inside diameter) within 2 h after baling. Core samples were dried to constant weight at 60°C in a forced air dryer.

Film was applied within 5 h after baling with a platform wrapper (Model UN7517, Kverneland ASA, Kverneland, Norway). Bales received two, four, or six layers of stretch-wrap plastic film (Sunfilm, AEPI Industries, South Hackensack, NJ), and all bales were placed in a single layer on a well-drained grass sod for storage. Copper-constantan thermocouples (TH-65 TC Thermometer System, Wescor International, Logan, UT) were inserted 0.4 m into each bale for temperature measurement and exit holes were sealed. Bale and ambient air temperatures were recorded daily during the first 2 wk, then at longer intervals during the remainder of the storage period. Bale dimensions were recorded on both the horizontal and vertical axes. To quantify the cylindrical variability of the bale, deformation was calculated for each bale as the ratio of the mean vertical to mean horizontal length (m m–1) (Mohsenin, 1970).

Bales from Trials 1 and 2 were weighed and sampled again on 11 December and 27 January, respectively, after a 5-mo storage period. Post-storage silage-bale core samples were split and one-half of the material was frozen for later determination of pH, lactic acid, volatile fatty acid, and nonprotein nitrogen (NPN). The remainder was dried at 60°C for 72 h and used for forage quality analysis. The depth of the weathered layer was measured for hay at the 12, 3, 6, and 9 o'clock positions on both ends of each bale. Bale bottom samples (6 o'clock) were processed and analyzed separately; the other positions were composited for each bale.

Dried samples were ground to pass a 4-mm screen, split to reduce sample volume, and reground to pass a 1-mm screen. Near infrared reflectance (NIR) spectra were obtained with a Pacific-Scientific (NIR Systems, Inc., Silver Spring, MD) Model 6250 reflectance scanning monochromator. Calibration equations were developed from one-half of the samples, analyzed for total nitrogen (N) with a semimicro Kjeldahl procedure (Bremner and Breitenbeck, 1983; Bradstreet, 1965) and for NDF, ADF, and ADL by the method of Goering and Van Soest (1970) as modified by Van Soest et al. (1991) and Komarek (1993). Crude protein was calculated as total N x 6.25. Total sugars (TS) were determined on a filtered water extract after mild acid hydrolysis by measuring reducing power by a ferricyanide-reduction method (Chatterton et al., 1987). Calibration statistics for NIR equations were as follows: NDF, SEC = 10.1, R2 = 0.976; SECV = 17.0, R2 = 0.93; ADF, SEC = 11.2, R2 = 0.96; SECV = 14.1, R2 = 0.93; ADL, SEC = 6.9, R2 = 0.91; SECV = 8.6, R2 = 0.85; CP, SEC = 2.3, R2 = 0.99; SECV = 1.8, R2 = 0.95; TS, SEC = 6.9, R2 0.91; SECV = 8.2, R2 = 0.87; where SEC = standard error of calibration and SECV = standard error of validation, in g kg–1 on a DM basis. Whole-bale values for hay forage quality constituents were weighted averages of quality data from both weathered and non-weathered fractions and were based on the proportion of the bale mass in each fraction.

Silage extracts were prepared by adding deionized water to 10 g of the silage samples (10:1 w/w), homogenizing for 30 s, and filtering through four layers of cheesecloth. Silage pH was determined on these water extracts immediately following filtration. The water extracts were then split to provide aliquots for analysis of lactic acid, volatile fatty acids, and NPN content. Lactic acid was determined on aliquots by an enzymatic method (Hohorst, 1963). Concentrations of acetate, propionate, isobutyrate, butyrate, isovalerate, and valerate were determined by gas chromatography using aliquots of these water extracts. Five milliliters of 25% (w/v) trichloroacetic acid (TCA) was added to a 20-mL aliquot of the filtrate to precipitate the protein from the sample. After 1 h at room temperature, the solution was centrifuged (25 000 x g for 25 min). Nitrogen in the centrate was determined by the micro-Kjeldahl method of Bremner and Breitenbeck (1983).

Shortly after post-storage sampling, the 12 bales from Trial 2 were used in a completely randomized feeding trial to assess the animal acceptance of the hay control compared with baled silage covered with different increments of plastic. Twelve overwintering 3-yr-old Angus beef cows, each weighing approximately 550 to 600 kg, were confined in a 2-ha paddock and given simultaneous, cafeteria-style access to four pre-weighed bales on tared pallets, one from each silage treatment and hay control. Before each feeding period, a single bale was randomly selected to include in the test of animal preference from each of the remaining bales in a treatment (feeding period confounded with replicate). Feeding periods commenced on 29 January, 19 February, 26 February, and 16 March. No other feed or supplements were made available, and the grass within the paddock remained dormant during the animal preference trial. Heavy-duty metal bale feeders (Tractor Supply Co., Brentwood, TN) of 2.4-m diameter were used to restrict animal access to bales. A feeding location of approximately 40 m2 was randomly chosen within the paddock, with the constraint that subsequent locations were placed in an area that provided stable footing and did not overlap. Bales were randomly arranged within the feeding location, with the constraint that bales were spaced at least 6 m apart. Twine and film were removed before feeding, but bales were not processed further. Unconsumed forage was weighed after a 5-d feeding period and sampled for dry matter analysis as previously described. Dry matter consumption was expressed as a percentage of initial bale dry weight.

Hay and silage data were analyzed by the MIXED procedure of SAS (SAS Institute, 1996). Pre-storage and post-storage silage data were analyzed as a completely random experiment with four replicates of a 2 x 3 factorial of moisture and film-amount treatments, with a hay control. Moisture concentration and film amount were considered fixed effects and trial was treated as a random effect. The autoregressive of order 1 covariance structure was used in the repeated measures analysis. Statistical significance was declared at the 0.05 level of confidence unless otherwise stated. Repeated measures analysis of variance was used to analyze time effects for bale temperatures and pre- and post-storage effects for forage quality constituents in hay and silage (SAS Institute, 1996). Significant (P < 0.05) trial x treatment interactions were present for several variables. Therefore, data from the two trials were analyzed and are presented separately.


   RESULTS AND DISCUSSION
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
CONCLUSIONS
 REFERENCES
 
Bale Temperature during Storage
Temporal variation and preservation treatment effects on bale temperatures were significant in both trials. In Trial 1, hay had lower (P < 0.05) temperatures than silage during Days 2 to 5 of storage (Fig. 1 ). Later, between Days 10 and 21 and beyond Day 35, hay had higher (P < 0.05) temperatures than did silage. After Day 2, hay in Trial 2 had higher temperatures (P < 0.05) than silage treatments until Day 59 of storage (Fig. 2 ). In Trials 1 and 2, hay temperature followed trends similar to the ambient air temperature (Fig. 1 and 2). Among silage treatments in Trial 1, bales with two layers of film maintained higher temperatures (P < 0.05) than bales with four or six layers of film regardless of moisture level, after an initial period of 10 d in which there were no differences (P > 0.10). Silage bales in Trial 2 prepared with two layers of film generally had higher temperatures than bales prepared with four or six layers of film. Layers of plastic film affected (P < 0.05) temperatures between Day 10 of storage and the end of the measurement period, except for Day 14 and 22. Elevated temperatures for bales covered with two layers of film suggest that higher levels of aerobic microbial activity or plant enzymatic respiration (Muck, 1999) occurred in these bales compared with those prepared with four or six layers of film. A few stems protruded through the film for bales wrapped with two layers of film but not for the four or six layer treatments.


Figure 1
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  		Fig. 1. Temperature profiles of alfalfa round bale silage prepared with two, four, and six layers of plastic film ensiled at two forage moisture levels, and a field-dried hay control in Trial 1, as compared with the ambient air temperature. Hay was baled at 166 g kg–1 dry matter.

 

Figure 2
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  		Fig. 2. Temperature profiles of alfalfa round bale silage prepared with two, four, and six layers of plastic film, and a field-dried hay control in Trial 2, as compared with the ambient air temperature. Bales were ensiled at 613 g kg–1 moisture and hay was baled at 198 g kg–1 moisture.

 
Dry Matter Losses and Bale Deformation during Storage
Dry matter losses during outside storage of hay averaged 153 g kg–1 in Trial 1 and 179 g kg–1 in Trial 2, somewhat less than losses previously reported by Belyea et al. (1985) for alfalfa hay packaged in round bales stored outside. Dry matter losses for round bale silage were generally low but highly variable, averaging 63 ± 64 g kg–1 in Trial 1 and 31 ± 47 g kg–1 in Trial 2 and confirm the advantage of silage over outside-stored hay for preserving crop DM in humid environments (McGechan, 1990). Treatment effects were absent for silage DM losses. Previous research with conventional or baled silage found somewhat higher storage losses of DM for silage than those measured in the present study (Robinson et al., 1988; McCormick et al., 1998). McCormick et al. (1998) reported DM losses of 89 g kg–1 for annual ryegrass (Lolium multiflorum L.) round bale silage of similar moisture to that in the present trials.

The average depth of weathered hay present at the end of Trial 1 was 5.1 cm, which was significantly (P < 0.01) less than the 9.8-cm depth measured at the end of Trial 2. Precipitation during the 5 mo storage periods for Trials 1 and 2 were 357 and 332 mm, respectively, but conditions for moisture evaporation were considerably better during Trial 1 (364 mm total open-pan evaporation) than during Trial 2 (102 mm). Both the silage and hay bales prepared for this experiment were relatively dense, 207 kg DM m–3 in Trial 1 and 187 kg DM m–3 in Trial 2. These values are similar to those reported for high-density bales by Russell et al. (1990), who reported greater hay storage losses for bales with lower density.

Maintenance of the original cylindrical shape of round bales stored on the ground is desirable as it minimizes the hay-soil interface and avoids tensile stresses on the plastic. In Trial 1, pre-storage hay bales exhibited greater deformation (P < 0.05) than bales wrapped in plastic with the exception of a similarity between the bales of the hay control, the two-layer film treatment for silage at 374 g kg–1 moisture and four layer treatment for silage at 502 g kg–1 moisture in Trial 1 (Table 1). In Trial 2, pre-storage hay bales were significantly more deformed (P < 0.05) than the six-layer treatment for silage, though the differences between the hay and two- or four-layer silage treatments were significant at P < 0.10. After storage, only the six-layer treatment of the 374 g kg–1 moisture silage was significantly (P < 0.05) less deformed than the hay control in Trial 1, and no differences were observed in Trial 2. All treatments in Trial 2 were significantly (P < 0.01) more deformed after storage than before storage. In Trial 1, there were no changes in deformation during storage. A closer evaluation revealed that, despite a similar (P > 0.10) decrease in vertical bale lengths in treatments in Trial 1 relative to those in Trial 2, the proportional changes in horizontal length were slightly greater (P < 0.10) in Trial 2 than in Trial 1 (data not shown). This discrepancy likely resulted from a difference in the tensile strength of the twines used in the two trials.


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  		Table 1. Pre-storage and post-storage bale deformation in alfalfa round bale silage and dry hay.

 
Forage Quality
Preservation treatment effects were absent for pre-storage concentrations of NDF, ADF, ADL, and CP in hay and silage bales in Trial 1 (P > 0.05) (Table 2). Pre-storage concentrations of TS in hay and silage from Trial 1 were also unaffected by subsequent preservation treatment and averaged 80 g kg–1. For Trial 2, hay had considerably higher (P < 0.01) concentrations of NDF, ADF, and ADL and lower concentrations of CP immediately after baling than pre-storage silage. This response was associated with two rainfall events (10.9 and 4.3 mm) that occurred during the intervening period between silage and hay baling for Trial 2. The negative effects of rain during curing on alfalfa hay yield and quality are well documented (Collins 1990, 1991) and are best demonstrated by the lower (P < 0.05) pre-storage concentrations of TS in hay (43.4 g kg–1) compared with silage bales for Trial 2 (64.7 g kg–1).


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  		Table 2. Pre-storage concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and crude protein (CP) for the treatment combinations in Trials 1 and 2.

 
The magnitude and direction of changes in forage quality during storage varied among preservation treatments, trials, and quality constituents (Tables 2 and 3). Neutral detergent fiber, ADF, and ADL increased more during storage in Trial 1 for hay and for silage with two layers of film than for other silages, causing significant differences between post-storage treatments, though none existed in pre-storage samples from the same trial. However, concentrations of ADL did not change during storage for any treatment (P > 0.05) in Trial 2, and slight decreases were measured during the storage period for NDF and ADF in silage and for ADF in hay. Concentrations of CP in the silage significantly increased (P < 0.05) in both two-layer treatments of Trial 1 during storage, but this change was not significantly affected (P > 0.05) by moisture concentration and was not significant (P > 0.05) in Trial 2. However, CP concentration in the hay control increased significantly during storage in both Trial 1 and 2 (155 vs. 164 g kg–1 and 182 vs. 193 g kg–1, respectively).


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  		Table 3. Post-storage concentrations of neutral detergent fiber (NDF), acid detergent fiber (ADF), acid detergent lignin (ADL), and crude protein (CP) for the treatment combinations in Trials 1 and 2.

 
Hay consistently had higher (P < 0.05) post-storage concentrations of NDF, ADF, and ADL than silage with four or six layers of film (Table 3). These data support other work that indicates that post-storage forage quality is better for silage than for round-baled hay made from the same crop (Johnson et al., 1984; Fraser et al., 1999). It should be noted that the loss of DM and reductions in forage quality during hay storage are greatly affected by the storage methods chosen (Collins et al., 1995). Collins et al. (1995) suggested that protection of hay from weathering reduces quality changes during storage. Outside storage was chosen in our studies to provide comparisons of silage with the typical hay storage methods used in the southeastern region of the USA.

Post-storage concentrations of NDF, ADF, and ADL in silage from Trial 1 were not affected by pre-storage moisture (P > 0.05). Averaged over silage moisture treatments in Trial 1, silage with two layers of film had higher (P < 0.01) post-storage concentrations of NDF, ADF, and ADL than silage prepared with more film. The lower forage quality, on the basis of NDF, ADF, and ADL concentrations, of the silage wrapped with two layers of film in Trial 1 is consistent with its bale temperature data, which indicated greater entry of oxygen during storage compared with silages prepared using four or six layers of film (Buckmaster et al., 1990, Huhnke et al., 1997). In contrast, film effects on post-storage concentrations of NDF, ADF, ADL, and CP in silage were absent (P > 0.05) in Trial 2. The cooler ambient temperatures prevailing in silage storage during Trial 2, which began in September, compared with those following the July initiation date of Trial 1 may have been a factor in this response. Additionally, silage fermentation data (Table 3) suggest that the slightly higher moisture concentrations of silage prepared for Trial 2 (relative to that of the moist silage treatment in Trial 1) may have led to enhanced fermentation of two-layer silage.

No significant treatment effect (P > 0.05) on post-storage concentrations of CP was observed in either trial (Tables 1 and 2). The absence of post-storage treatment differences in CP for Trial 2, in contrast to the pre-storage situation, illustrates a previously documented phenomenon in which CP concentration increases following heavy losses of other more readily removed non-protein constituents from hay (Rotz and Abrams, 1988).

Silage Quality
Silage pH was higher (P < 0.05) in the lower-moisture silage that was wrapped with two layers of film in Trial 1 (Table 4) compared with other silages. Otherwise, there were no preservation treatment effects on silage pH in either trial.


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  		Table 4. Silage quality parameters of alfalfa round bale silage of varying moisture concentrations and wrapped with two, four, or six layers of polyethlyelene plastic film.

 
There was a large difference (P < 0.001) in the NPN concentration of Trials 1 and 2 (359 vs. 590 g kg–1 total N, respectively). This can largely be explained by the difference in moisture at ensiling, described by Muck (1987), but differences in the relative amount of CP in the two trials may have also contributed to this observation. In Trial 1, there was a significant effect (P < 0.05) of moisture on NPN concentration, as the 502 g kg–1 moisture treatment was consistently higher than the 374 g kg–1 moisture treatment (391 vs. 328 g kg–1 total N, respectively). The effect of increasing plastic coverage was only slightly significant (P < 0.10), but the two-layer treatments had slightly lower NPN levels than the four- or six-layer treatments (315 vs. 386 and 377 g kg–1 total N, respectively) in Trial 1. This is in agreement with Muck (1999) who found lower concentrations of NPN at a 5-cm depth beneath an air-exposed surface of alfalfa silage compared with concentrations at greater depths where oxygen levels were lower. Concentrations of NPN for the four and six-layer treatments in Trial 2 are consistent with values for ensiled alfalfa reported by Owens et al. (1999), while the two-layer treatment in Trial 2 and all treatments in Trial 1 were lower.

Moisture effects on the concentration of lactic acid were largely absent (P > 0.05) in Trial 1. In the 374 g kg–1 moisture treatment, silage prepared with two layers of film had higher (P < 0.05) lactic acid concentrations than silage wrapped with more film (Table 4). However, the opposite effect of plastic occurred in the silage prepared at 502 g kg–1 moisture. Lactic acid concentrations were considerably higher, but unaffected by preservation treatment, in Trial 2 compared with Trial 1. Kung et al. (2003) reported similar values for lactic acid (41.2 g kg–1 DM) and pH (4.38) for non-inoculated, chopped alfalfa ensiled at a similar concentration of moisture (610 g kg–1).

Propionic and acetic acids were the major volatile fatty acid constituents of silages from both trials (Table 3). Butyric acid concentrations varied widely (0.24 to 1.00 g kg–1) among trials and preservation treatments and showed no consistent treatment response.

Animal Preference Evaluation
Cows consumed more (P < 0.05) DM and a larger (P < 0.001) proportion of the available DM from the silage bales prepared with four or six layers of film than that prepared as dry hay during successive 5-d feeding periods when provided these forages cafeteria-style (Table 5). Work by Han et al. (2004) evaluated the intake of outside-stored alfalfa hay relative to baled alfalfa silage and showed a similar reduction in DM intake as hay. Among silage treatments, bales wrapped with four or six layers of film were consumed to a greater (P < 0.001) extent than silages wrapped with two layers of film. No difference (P > 0.05) was found between consumption of silages wrapped with four and six layers of film. Thus, even though laboratory analyses failed to show differences in pH, lactic acid, propionic acid, or acetic acid among the silages produced in Trial 2, these data show that the animals distinguished and discriminated (P < 0.001) against silages with two layers of film compared with four or six layers and preferred silage prepared with at least four layers of plastic.


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  		Table 5. The mean actual dry matter and percentage of available dry matter consumed of each bale by 12 Angus cows during a 5 d feeding trial comparing silage bales wrapped with two, four, or six layers of plastic film and dry hay.

 

   CONCLUSIONS
TOP
 NOTES
 ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
REFERENCES
 
On the basis of forage quality, silage quality, and animal consumption data, we conclude that two layers of film are not adequate for preservation of alfalfa round bale silage. The absence of consistent differences between silages wrapped with four and six layers of film leads us to conclude that four layers optimizes coverage under conditions similar to those of our trials. Further work is needed to determine whether differences exist between baled silages prepared with four or six layers of film over longer storage periods or at other moisture levels.

We conclude that alfalfa round bale silage is superior in forage quality and animal preference to alfalfa hay stored outside without cover. The silage preservation system was superior to hay in DM retention during storage and in forage quality available for feeding.


   ACKNOWLEDGMENTS
 
The authors thank Dr. Charles Dougherty for the use of his cows in the feeding trial. The advice and consultation of Dr. Glen Aiken, Research Animal Scientist with the USDA-ARS Forage-Animal Production Research Unit in Lexington, KY, and Dr. Paul Cornelius, Professor of Statistics jointly in the Plant and Soil Sciences and Statistics departments at the University of Kentucky, is gratefully acknowledged.


   NOTES
TOP
 NOTES
ABSTRACT
 INTRODUCTION
 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 
Submitted with the approval of the Director, KY Agric. Exp. Stn. as publication 05-05-002.

Received for publication March 3, 2005.


   REFERENCES
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 NOTES
 ABSTRACT
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 MATERIALS AND METHODS
 RESULTS AND DISCUSSION
 CONCLUSIONS
 REFERENCES
 




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The SCI Journals Agronomy Journal Vadose Zone Journal
Journal of Natural Resources
and Life Sciences Education		 Soil Science Society of America Journal
Journal of Plant Registrations Journal of
Environmental Quality		 The Plant Genome