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Corn Silage Management: Effects of Hybrid, Maturity, Inoculation, and Mechanical Processing on Fermentation Characteristics

L. M. Johnson^*, J. H. Harrison^*, D. Davidson^*, W. C. Mahanna and K. Shinners

^* Department of Animal Sciences, Washington State University, Puyallup 98371
Pioneer Hi-Bred International, Des Moines, IA 50131
Department of Biological System Engineering, University of Wisconsin, Madison 53706

Corresponding author:
Dr. Joe Harrison; e-mail:
harrison{at}puyallup.wsu.edu.

	ABSTRACT

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Two experiments were conducted to evaluate the effects of hybrid, maturity, mechanical processing, and inoculation of corn silage on fermentation characteristics. In experiment 1, Pioneer hybrid 3845 corn silage was harvested at three maturities (hard dough, one-third milkline, two-thirds milkline). In experiment 2, Pioneer hybrids 3845 and Quanta were harvested at three maturities (one-third milkline, two-thirds milkline, and blackline). In both experiments, corn silage was harvested at each maturity with and without mechanical processing and with and without inoculation. In experiments 1 and 2, corn silage was harvested at a theoretical length-of-cut of 6.4 and 12.7 mm, respectively. Maturity at harvest tended to have a greater impact on silage fermentation characteristics of corn silage than mechanical processing and inoculation. In experiments 1 and 2, corn silage harvested at the earliest maturity tended to have decreased dry matter content and increased water-soluble carbohydrate concentrations during the ensiling process than corn silage harvested at advanced maturities. In experiment 2, pH levels were lower for corn silage harvested at the early maturity (one-third milkline) compared with advanced maturities (two-thirds milkline and blackline) by 57 d after ensiling. The difference in pH can be explained by the greater concentration of water-soluble carbohydrates at the early maturity (one-third ML) soon after ensiling (2, 3, 6 and 10 d after ensiling) compared with advanced maturities (two-thirds ML and BL). The increased water-soluble carbohydrate concentrations in the less mature corn silage provided nutrients for bacteria to grow and produce primarily lactic acid (6, 10, and 57 d after ensiling) and some acetic acid (2, 3, 6, and 10 d after ensiling) which reduced the pH of corn silage more than at the advanced maturities. There was a slight change in silage fermentation characteristics when corn silage was inoculated with Pioneer 1132 inoculant in experiment 1. The inoculated corn silage had increased temperature, lactate and acetate concentrations, and lower water-soluble carbohydrate and pH levels compared with uninoculated corn silage. Dry matter recovery tended to be greater for processed corn silage in experiment 1, and greater for unprocessed corn silage in experiment 2. It appears that when fermentation was greater (increased temperature and lactate concentration 57 d after ensiling) the dry matter recovery was lower.

Key Words: corn silage • inoculation • mechanical processing • maturity

Abbreviation key: BL = blackline, ML = milkline, WSC = water-soluble carbohydrates

	INTRODUCTION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Many factors of corn silage management can influence silage fermentation characteristics. Studies have demonstrated some of the chemical changes that occur in the corn plant as it matures that leads to less fermentable substrates being available for lactic acid producing bacteria (McDonald et al., 1991). As the corn plant matures, water-soluble carbohydrate (WSC) levels decrease and the starch levels increase in whole-plant corn. Therefore, there is less fermentable substrate available for lactic acid producing bacteria to consume. This has the potential of delaying fermentation. Several studies have demonstrated the effects of inoculation of corn silage on silage fermentation characteristics (Harrison et al., 1996; Higginbotham et al., 1998; Cai et al., 1999; Ranjit and Kung et al., 2000). A summary of 17 studies that used corn silage inoculants demonstrated a numerical increase in lactic acid levels, and a significant reduction in pH of fermented corn silage that utilized an inoculant (Harrison et al., 1996).

Other studies have reported that chop length and degree of crop maceration can influence silage fermentation characteristics (personal communication with Richard Muck). Short chop length or increased maceration has increased the rate of lactic acid bacteria proliferation, increased the rate of pH reduction, and lowered final pH (personal communication with Richard Muck). However, only one study has been published on the effects of mechanical processing of corn silage on silage fermentation characteristics (Johnson et al., 1997). Because there has been rapid adoption of mechanical processing of corn silage prior to ensiling in the US over the last 5 yr, it is important to characterize changes that occur in the silo due to processing, and to interactions of processing with maturity, inoculation, and corn silage hybrid.

The objective of this study was to evaluate the effects of hybrid, maturity, mechanical processing, and inoculation of corn silage on silage fermentation characteristics and DM recovery.

	MATERIALS AND METHODS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Experimental Design
Two experiments were conducted using mini-silos to evaluate the effects of hybrid, stage of maturity, mechanical processing, and inoculation of corn silage on silage fermentation characteristics and DM recovery. Experiment 1 was a 2 x 2 x 3 factorial arrangement; experiment 2 was a 2 x 2 x 2 x 3 factorial. In experiment 1, there was one hybrid of corn silage (Pioneer hybrid 3845), and in experiment 2 there were two hybrids of corn silage (Pioneer hybrids 3845 and Quanta). In both experiments, corn silage was harvested at three maturities. Within each maturity, corn silage was harvested with and without mechanical processing and with and without inoculation. In experiment 1, each treatment (maturity by processing by inoculation) was ensiled in triplicate, and in experiment 2, each treatment (hybrid x maturity x processing x inoculation) was ensiled in duplicate.

Two hybrids of corn silage were chosen in experiment 2 to evaluate the effects of maturity, processing, and inoculation on silage fermentation of corn silage that differed in silage characteristics. Hybrid Quanta is a flint corn and hybrid 3845 is a dent corn. Hybrid Quanta tends to have higher DM and starch content at the same maturity as hybrid 3845. Flint corn also tends to have a greater percentage of vitreous starch than dent corn. This starch tends to be less digestible because it contains starch that is embedded in a protein matrix (Kortarski et al., 1992).

In all experiments, corn silage was harvested with a self-propelled John Deere 5830 harvester (with a kernel processing unit) at a ground speed between 3.2 and 4.0 km/h. The processing equipment was fully active (two counter-rotating rolls positioned between the cutterhead and blower with their axis of rotation parallel to the cutterhead). The harvester consisted of four knives per row, and there were 10 tangential rows. At each stage of maturity, corn silage was harvested with the kernel processing rolls set 1 mm apart (processed), and with the kernel processing rolls set 15.9 mm apart (unprocessed). In experiments 1 and 2, the inoculated treatments were treated with Pioneer 1132 corn silage inoculant (Pioneer Hi-Bred Intl., Des Moines, IA). In experiments 1 and 2, inoculant was applied as a fine mist at a standard rate of 1.0 x 10⁵ cfu of fresh forage. During inoculant application, the corn silage was mixed manually. In experiments 1 and 2, an equal amount of water was sprayed onto the forage treatments that did not require inoculation.

Experiments 1 and 2.
In experiment 1, hybrid 3845 corn silage was harvested during the 1996 growing season in western Washington. Corn silage was harvested at hard dough (23.5% DM), one-third milkline [ML; 25.0% DM], and two-thirds ML (29.3% DM-with two light frosts and one killing frost) stages of maturity (experiment 1). The TLC for the corn silage was 6.4 mm (harvester set with 10 rows of knives and a 12-tooth sprocket; experiment 1). In experiment 2, hybrid 3845 corn silage was harvested in western Washington during the 1997 growing season at one-third ML (25.3% DM), two-thirds ML (31.3% DM), and blackline [BL; 33.4% DM] stages of maturity. In experiment 2, hybrid Quanta corn silage was harvested during the 1997 growing season in western Washington. Corn silage was harvested at one-third ML (26.8% DM), two-thirds ML (34.0% DM), and BL (41.3% DM) stages of maturity. The TLC for the corn silage in experiment 2 was 12.7 mm (chopper set with 10 rows of knives and a 24-tooth sprocket). Corn silage was stored in 20-L pails (29 cm x 35 cm, height x diameter) with double-lined plastic liner to ensure anaerobic conditions. Each silo held approximately 5 to 6 kg of wet corn silage.

Sample Collection, Preparation, and Analysis
In experiments 1 and 2, a pre-ensiled sample of the whole corn plant for each treatment was dried at 55°C in a forced-air oven and analyzed for DM (Tables 1 through 3). Dried, pre-ensiled, whole-plant corn was ground through a 1-mm screen using a Wiley mill (Arthur H. Thomas, Philadelphia, PA) and analyzed for WSC (Dubois et al., 1956; Tables 1 through 3). In experiments 1 and 2, a composited sample of wet, pre-ensiled, whole-plant corn, was analyzed for pH for each treatment, using a portable pH meter (Digital Mini-pH-meter, model 55, VWR Scientific, Inc.; Tables 1 through 3).

where µ = overall mean, T_i = treatment effect (experiment 1: i = 1 to 12; experiment 2: i = 1 to 24), and E_i = error term. Treatment means are reported in Tables 7 through 13.

where µ = overall mean; R_i = replication (i = 1 to 3); M_j = maturity effect (j = 1 to 3); K_k = kernel processing effect (k = 1 to 2); I_l = inoculation effect (l = 1 to 2); (M x K)_jk = interaction effect of M_j and K_k; (M x I)_jl = interaction effect of M_j and I_l; (K x I)_kl = interaction effect of K_k and I_l; and E_ijkl = error term. The P values for the main effects and interaction terms are reported in Tables 7 through 13.

The model for analyzing repeated measures in experiment 1 was:

where µ = overall mean; R_i = replication (i = 1 to 3); M_j = maturity effect (j = 1 to 3); K_k = kernel processing effect (k = 1 to 2); I_l = inoculation effect (l = 1 to 2); (M x K)_jk = interaction effect of M_j and K_k; (M x I)_jl = interaction effect of M_j and I_l; (K x I)_kl = interaction effect of K_k and I_l; (R x M x K x I)_ijkl error term for all whole-plot sources of variation; D_m = day after ensiling (m = 1 to 5); (M x D)_jm = interaction effect of M_j and D_m; (K x D)_km = interaction effect of K_k and D_m; (I x D)_lm = interaction effect of I_l and D_m; (M x K x D)_jkm = interaction of M_j, K_k, and D_m; (M x I x D)_jlm = interaction of M_j, I_l, and D_m; (K x I x D)_klm = interaction of K_k, I_l, and D_m; and E_ijklm = error term for sub-plot (time) sources of variation.

The model to test for main effect and interaction differences in experiment 2 was:

where µ = overall mean; R_i = replication (i = 1 to 2); H_j = hybrid effect (j = 1 to 2); M_k = maturity effect (k = 1 to 3); K_l = kernel processing effect (l = 1 to 2); I_m = inoculation effect (m = 1 to 2); (H x M)_jk = interaction effect of H_j and M_k; (H x K)_jl = interaction effect of H_j and K_l; (H x I)_jm = interaction effect of H_j and I_m; (M x K)_kl = interaction effect of M_k and K_l; (M x I)_km = interaction effect of M_k and I_m; (K x I)_lm = interaction effect of K_l and I_m; and E_ijklm = error term. The P values for the main effects and interaction terms are reported in Tables 7 through 13.

The model for analyzing repeated measures in experiment 2 was:

where µ = overall mean; R_i = replication (i = 1 to 2); H_j = hybrid effect (j = 1 to 2); M_k = maturity effect (k = 1 to 3); K_l = kernel processing effect (l = 1 to 2); I_m = inoculation effect (m = 1 to 2); (H x M)_jk = interaction effect of H_j and M_k; (H x K)_jl = interaction effect of H_j and K_l; (H x I)_jm = interaction effect of H_j and I_m; (M x K)_kl = interaction effect of M_k and K_l; (M x I)_km = interaction effect of M_k and I_m; (K x I)_lm = interaction effect of K_l and I_m; (R x H x M x K x I)_ijklm error term for all whole-plot sources of variation; D_n = day after ensiling (n = 1 to 5); (H x D)_jn = interaction effect of H_j and D_n; (M x D)_kn = interaction effect of M_k and D_n; (K x D)_ln = interaction effect of K_l and D_n; (I x D)_mn = interaction effect of I_m and D_n; (H x M x D)_jkn = interaction effect of H_j, M_k, and D_n; (H x K x D)_jln = interaction effect of H_j, K_l, and D_n; (H x I x D)_jmn = interaction effect of H_j, I_m, and D_n; (M x K x D)_kln = interaction of M_k, K_l, and D_n; (M x I x D)_kmn = interaction of M_k, I_m, and D_n; (K x I x D)_lmn = interaction of K_l, I_m, and D_n; and E_ijklmn = error term for sub-plot (time) sources of variation.

The model for regression analyses in experiments 1 and 2 was:

where ß₀ = intercept on the Y axis; ß₁, ß₂, ß₃, ..., ß_x = regression coefficients for multiple variables; X₁, X₂, X₃, ..., X_x = prediction variables; and E_i = error term. Significance was declared at P < 0.05 and trends were observed at P < 0.10 for all statistical models in this paper (SAS, 1988).

	RESULTS AND DISCUSSION

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Maturity
In experiments 1 and 2, the pre-ensiled DM concentration increased and the WSC concentration tended to decrease as maturity of pre-ensiled whole-plant corn advanced (Tables 1 through 3). This was similar to other published data where the whole-plant corn DM concentration increased and sugar concentration decreased as maturity advanced (Xu et al., 1995; Hunt et al., 1989). In experiments 1 (P < 0.0001) and 2 (Quanta, P < 0.0001 and 3845, P < 0.006), as maturity advanced, the DM concentration of postensiled corn silage increased (Table 7).

Final temperature of the different treatments of corn silage varied from 11 to 19°C (Table 8). These temperatures were within the range in which respiration occurs at a rapid rate (Muck and Pitt, 1993). Muck and Pitt (1993) reported that respiration slows as temperature increases from 24 to 46°C and stops at 54°C. Corn silage harvested at two-thirds ML in both experiments tended to have temperatures that stayed elevated through 57 d after ensiling (15.5 to 18°C; Figures 1a through 1c). Corn silage harvested at the earliest maturity in both experiments (hard dough-experiment 1 and one-third ML-experiment 2) had temperatures that stayed elevated (16 to 19°C) through 10 d after ensiling, and then declined by 57 d after ensiling (14 to 15°C; Figures 1a through 1c).

View larger version (26K): [in this window] [in a new window]   Figure 1. Temperature plotted across days after ensiling for corn silage harvested at different maturities in experiment 1 [Figure 1a—hard dough (), one-third milkline (), and two-thirds milkline () stages of maturity in experiment 1], for hybrid 3845 in experiment 2 [Figure 1b—one-third milkline (), two-thirds milkline (), and blackline ()], and for hybrid Quanta in experiment 2 [Figure 1c—one-third milkline (), two-thirds milkline (), and blackline ()].

In experiment 2, there was an interaction of time (days after ensiling) with hybrid and maturity for temperature of corn silage (d 2 to d 3, P < 0.005; d 3 to d 6, P < 0.007; d 6 to d 10, P < 0.0001; d 10 to d 57, P < 0.0001). Temperature decreased at a faster rate (between 2 and 6 d after ensiling) for corn harvested at physiological maturity (BL) than at earlier maturities (one-third and two-thirds ML) with both hybrids in experiment 2 (Figures 1b and 1c). Also, the temperature of hybrid Quanta corn silage harvested at BL dropped at a faster rate than hybrid 3845 corn silage harvested at BL between 2 and 6 d after ensiling (Figures 1b and 1c). The drier silage tended to have temperatures that declined at a faster rate than wetter silage in experiment 2. This may be an indication that there was less microbial activity in the drier silage.

Water-soluble carbohydrate concentrations in the corn differed among maturities in experiments 1 and 2 (Table 9). Corn harvested at the earliest maturity in both experiments had significantly greater concentrations (P < 0.0001 at d 2, 3, 6, and 10 for both experiments) of WSC 2, 3, 6, and 10 d after ensiling than corn harvested at advanced maturities (Figures 2a through 2c). However, the difference in WSC concentration between the earliest maturity and the two advanced maturities in both experiments became less as days after ensiling advanced (Figures 2a through 2c). The greater levels of WSC in postensiled corn silage (Table 9) harvested at early maturities was related to the greater level of WSC in pre-ensiled whole corn at early maturities (Tables 1 through 3). The whole corn plant has greater levels of sugars when it is immature. As the corn plant matures, the corncob and kernels develop, starch levels increase, and the amount of sugars present in the whole corn plant decrease. Increased levels of sugar in the corn silage help to promote a rapid fermentation, because the sugar compounds are an excellent source of energy for lactic acid producing bacteria. Therefore, it is common for less mature corn silage to go through a rapid fermentation process because there is a greater level of rapidly fermentable substrate available.

View larger version (29K): [in this window] [in a new window]   Figure 2. Water-soluble carbohydrate concentration plotted across days after ensiling for corn silage harvested at different maturities in experiment 1 [Figure 2a—hard dough (), one-third milkline (), and two-thirds milkline () stages of maturity in experiment 1], for hybrid 3845 in experiment 2 [Figure 2b—one-third milkline (), two-thirds milkline (), and blackline ()], and for hybrid Quanta in experiment 2 [Figure 2c—one-third milkline (), two-thirds milkline (), and blackline ()].

View larger version (26K): [in this window] [in a new window]   Figure 3. Lactate concentration plotted across days after ensiling for corn silage harvested at different maturities in experiment 1 [Figure 3a—hard dough (), one-third milkline (), and two-thirds milkline () stages of maturity in experiment 1], for hybrid 3845 in experiment 2 [Figure 3b—one-third milkline (), two-thirds milkline (), and blackline ()], and for hybrid Quanta in experiment 2 [Figure 3c—one-third milkline (), two-thirds milkline (), and blackline ()].

There was a time x maturity interaction for lactate concentration as d advanced from 2 to 3 (P < 0.05) and a time by hybrid x maturity interaction as d advanced from 6 to 10 (P < 0.003) in experiment 2. The lactate concentration in the corn increased more at the early maturity (one-third ML) as d advanced from 2 to 3 than the advanced maturities (two-thirds ML and BL; 0.91 vs. 0.39 and 0.32 percentage units for one-third ML, two-thirds ML and BL, respectively; Figures 3b and 3c). Both hybrids had lactate concentrations that increased more at one-third ML than advanced maturities (two-thirds ML and BL) as d advanced from 6 to 10. However, there was a greater increase in the lactate concentration at one-third ML as d advanced from 6 to 10 for hybrid 3845 than hybrid Quanta (1.37 vs 0.35 percentage units; Figures 3b and 3c). The increased production of lactate soon after ensiling for corn harvested at one-third ML may be partially related to more WSC being available for consumption by lactate producing bacteria present in the corn (Table 9).

Acetate concentration was significantly affected by corn silage maturity in experiments 1 and 2 (Table 11). However, many times the absolute difference between maturities was small at a given time point (Figure 4a through 4c). In experiment 1, the acetate concentration decreased as maturity advanced (Table 11). The acetate concentration was greater for corn silage harvested at hard dough than one-third ML, and corn silage harvested at one-third ML had greater acetate concentrations than at two-thirds ML at 2 (P < 0.0001 and P < 0.0001), 3 (P < 0.005 and P < 0.07), 6 (P < 0.0001 and P < 0.003) and 10 (P < 0.008 and P < 0.007) d after ensiling (Table 11; Figure 4a). In experiment 2, acetate concentration was greater for corn silage harvested at the earliest maturity (one-third ML) compared with physiological maturity (BL) at 2 (P < 0.0007), 3 (P < 0.0001), 6 (P < 0.0002), and 10 (P < 0.0001) d after ensiling. There was a hybrid x maturity interaction (P < 0.02) at 10 d after ensiling for acetate concentration in corn. Hybrid 3845 had a rapid increase in acetate concentration on d 10 after ensiling compared with hybrid Quanta (Figures 4b and 4c). As d advanced to 57 the acetate concentration was greater in the medium maturing corn silage than the early and advanced maturing corn silage in experiment 1 (P < 0.0001; Figure 4a), and there was no difference in acetate concentration across corn silage maturities in experiment 2. The greater increase in acetate concentration for the medium maturing silage compared with the early maturing silage, in experiment 1, is unknown. However, it is an indication that there is still microbial activity occurring in the silage that is causing production of acetate between d 10 and 57.

View larger version (25K): [in this window] [in a new window]   Figure 4. Acetate concentration plotted across days after ensiling for corn silage harvested at different maturities in experiment 1 [Figure 4a—hard dough (), one-third milkline (), and two-thirds milkline () stages of maturity in experiment 1], for hybrid 3845 in experiment 2 [Figure 4b—one-third milkline (), two-thirds milkline (), and blackline ()], and for hybrid Quanta in experiment 2 [Figure 4c—one-third milkline (), two-thirds milkline (), and blackline ()].

These results suggest that the rate of fermentation was greater for the less mature corn silage, therefore there was a greater concentration of acetate early after ensiling (2, 3, 6, 10 d). Acetate was being formed at a slower rate by microbes in corn harvested at advanced stages of maturity. Therefore, by the time fermentation was complete (approximately 60 d after ensiling) the acetate concentration tended to be similar across corn silage maturities.

The ethanol concentration was affected by maturity of corn silage in both experiments (Table 12). Corn silage harvested at the earliest maturity had lower concentrations of ethanol than the medium maturing silage at 2 (P < 0.02), 3 (P < 0.0003), 6 (P < 0.0001), and 10 (P < 0.0001) d after ensiling in experiment 1, and at 2 (P < 0.0001) and 3 (P < 0.009) d after ensiling in experiment 2 (Table 12). Ethanol concentrations of corn silage harvested at the earliest maturity (hard dough) were lower than at the advanced maturity (two-thirds ML) in experiment 1, also. By 57 d after ensiling there was a hybrid x maturity interaction, and the ethanol concentration was greatest (P < 0.0001) for the corn silage harvested at the earliest maturity (one-third ML) compared with advanced maturities (two-thirds ML and BL) for hybrid 3845 in experiment 2.

View larger version (26K): [in this window] [in a new window]   Figure 5. pH plotted across days after ensiling for corn silage harvested at different maturities in experiment 1 [Figure 5a—hard dough (), one-third milkline (), and two-thirds milkline () stages of maturity in experiment 1], for hybrid 3845 in experiment 2 [Figure 5b—one-third milkline (), two-thirds milkline (), and blackline ()], and for hybrid Quanta in experiment 2 [Figure 5c—one-third milkline (), two-thirds milkline (), and blackline ()].

The changes in pH of corn over time after ensiling can be explained by WSC and acetic and lactic acid production in experiment 2. Both hybrids of corn silage harvested at the early maturity (one-third ML) had a greater concentration of WSC early after ensiling (2, 3, 6, and 10 d) compared with advanced maturities (two-thirds ML and BL; experiment 2; Figures 2b and 2c). The greater concentration of WSC provides increased nutrients for homofermentative and heterofermentative bacteria to consume and produce primarily lactic acid and some acetic acid. Lactic acid concentrations were greater at one-third ML compared with two-thirds ML and BL at 6, 10, and 57 d after ensiling (experiment 2; Figure 3b and 3c). Acetate concentration was greater for corn silage harvested at one-third ML compared with BL at 2, 3, 6, and 10 d after ensiling (experiment 2; Figures 4b and 4c). Others have reported a decline in lactate (Bal et al., 1997; Huber et al., 1968; Johnson et al., 1997), acetate (Bal et al., 1997; Huber et al., 1968), and ethanol (Bal et al., 1997) as maturity advanced. McDonald et al. (1991) suggested that pH tends to increase and organic acids tend to decline as maturity advances because there are less fermentable substrates available.

Mechanical Processing
Mechanical processing had a minimal effect on silage fermentation characteristics in experiments 1 and 2 (Tables 7 through 13). In experiment 2, the DM concentration was significantly greater (P < 0.0001) for unprocessed corn silage at all time points of ensiling than processed corn silage. In experiments 1 and 2, there were no statistical differences in temperature between processed and unprocessed corn silage until 57 d after ensiling (Table 8). The unprocessed corn silage (16.4°C) stayed warmer than the processed corn silage (13.9°C) at 57 d after ensiling in experiment 1 (Figure 6). The opposite trend was reported in experiment 2. However, the difference in temperature was small (0.5°C), and it is difficult to interpret the biological impact of a small difference in temperature on silage fermentation characteristics. Water-soluble carbohydrate concentrations were similar between processed and unprocessed corn silage 6, 10, and 57 d after ensiling in experiment 1, and were similar at all days after ensiling in experiment 2 (Table 9).

View larger version (18K): [in this window] [in a new window]   Figure 6. Temperature plotted across days after ensiling for corn silage that was processed () or unprocessed () in experiment 1.

View larger version (28K): [in this window] [in a new window]   Figure 7. Lactate concentration plotted across days after ensiling for corn silage that was processed () and unprocessed () in experiment 1 (Figure 7a), and processed () and unprocessed () in experiment 2 (Figure 7b).

View larger version (19K): [in this window] [in a new window]   Figure 8. Water-soluble carbohydrate concentration plotted across days after ensiling for corn silage that was processed () and unprocessed () in experiment 1.

Acetate concentration in corn silage did not follow similar trends to lactate and ethanol concentrations in experiments 1 and 2 (Tables 10 through 12). Processed corn silage had significantly greater acetate concentrations at 6 (P < 0.0004) and 10 (P < 0.0001) d after ensiling in experiment 1, at 2 (P < 0.02) d after ensiling in experiment 2, and at 3 (P < 0.0008) and 6 (P < 0.0003) d after ensiling for hybrid Quanta in experiment 2 (Table 11). Also, hybrid 3845 processed corn silage had a significantly lower acetate concentration at 10 (P < 0.001) d after ensiling than unprocessed corn silage in experiment 2 (Table 11). By 57 d after ensiling, acetate concentrations for processed and unprocessed corn silage were similar. The absolute differences were small (0.02 to 0.38 percentage units) for all the comparisons where acetate concentrations in processed corn silage were greater than unprocessed corn silage, and it is difficult to determine the biological impact of the differences. Others have reported acetate concentrations for processed corn silage that were greater [Johnson et al., 1997: one-third (P < 0.04) and two-thirds ML (P < 0.04); Weiss and Wyatt, 2000: conventional hybrid], lower (Weiss and Wyatt, 2000: high oil hybrid), or similar (Rojas-Bourrillon et al., 1987; Johnson, 1996; Johnson et al., 1997: hard dough) to unprocessed corn silage. However, once again, these differences were minimal and probably biologically insignificant.

In experiment 1, lactate concentration in the processed corn silage tended to be lower, whereas acetate concentration tended to be greater than unprocessed corn silage (Tables 10 and 11). These results suggest that with wetter corn silage, processing may promote greater acetate concentrations. However, in experiment 2 (hybrids 3845 and Quanta), lactate and acetate concentrations in the corn silage followed similar patterns within a hybrid. If lactate levels were greater for processed corn silage than acetate levels would also be greater (Tables 10 and 11). The growing and harvest conditions were drier in experiment 2, therefore the plants matured more rapidly and were drier at harvest. These factors may have contributed to the trends observed in experiment 2.

The pH decline over time was similar between processed and unprocessed corn silage in experiments 1 and 2 (Table 13). There were two situations in each experiment where pH differences reached statistical significance. However, the absolute differences were small (-0.01 to 0.06 pH units), and it is difficult to determine the biological impact. Overall, the differences between VFA and lactate concentrations in processed and unprocessed corn silage did not lead to differences in pH of the corn silage.

There were time x processing interactions for silage fermentation characteristics in this study. However, the change in silage fermentation characteristics (lactate, acetate, WSC, and pH) between days for processed and unprocessed corn silage didn’t follow consistent patterns, and many times the absolute values, although statistically different, did not have wide numerical differences between processed and unprocessed silage. There was a significant (P < 0.0001) time x processing interaction for temperature of corn silage between d 10 and d 57 in experiment 1. The temperature of unprocessed corn silage increased from d 10 to 57 by 1.1°C, and the temperature of processed corn silage decreased from d 10 to 57 by 1.5°C. The difference in temperature over time is an indication that there may have been more microbial activity between d 10 and 57 in the unprocessed corn silage in experiment 1.

Inoculation
Inoculation had a minor effect on corn silage fermentation characteristics in experiments 1 and 2 (Tables 7 through 13). Uninoculated corn silage tended to have a greater DM concentration than inoculated corn silage at 2 (P < 0.0003), 3 (P < 0.08), 6 (P < 0.0001), and 10 (P < 0.0001) d after ensiling in experiment 1, and at 10 (P < 0.05) and 57 (P < 0.02; Table 7) d after ensiling in experiment 2. The temperature of corn silage treated with Pioneer inoculant 1132 was greater at 2 (P < 0.0004), 10 (P < 0.0001), and 57 (P < 0.0002) d after ensiling compared with uninoculated corn silage by 1°C, 1.4°C, and 1.9°C, respectively, in experiment 1 (Figure 9). However, there were no significant differences in temperature between inoculated and uninoculated corn silage at all time points in experiment 2 (Table 8). Water-soluble carbohydrate concentrations were greater for uninoculated corn silage at 2 (P < 0.05), 3 (P < 0.001), and 10 (P < 0.003) d after ensiling in experiment 1 (Table 9). However, in experiment 2, WSC concentration tended to be similar between inoculated and uninoculated corn silage at all time points except for hybrid 3845 at d 10 (Table 9). Hybrid 3845 uninoculated corn silage had a greater (P < 0.08) concentration of WSC than inoculated corn silage 10 d after ensiling in experiment 2 (Table 9).

View larger version (18K): [in this window] [in a new window]   Figure 9. Temperature plotted across days after ensiling for corn silage that was inoculated () and uninoculated () in experiment 1.

View larger version (14K): [in this window] [in a new window]   Figure 10. pH plotted across days after ensiling for corn silage that was inoculated () and uninoculated () in experiment 1.

There was a significant time x inoculation interaction for temperature and pH in experiment 1 (Figures 9 and 10). However, in experiment 2, the only significant interaction of time with inoculation was for WSC concentration in corn silage, and the absolute differences were small. In experiment 1, inoculated corn silage cooled (0.7°C) from d 2 to d 3, whereas uninoculated corn silage heated (0.6°C) from d 2 to d 3 (Figure 9). Also, there was a large drop in temperature between d 6 and d 10 for uninoculated corn silage (1.7°C) compared with inoculated corn silage (0.2°C) in experiment 1 (Figure 9). The change in pH differed among inoculated and uninoculated corn silage between d 2 and d 3 (P < 0.0001), d 3 and d 6 (P < 0.001), d 6 and d 10 (P < 0.0001), and d 10 and d 57 (P < 0.0001; Figure 10). However, there was no consistent trend among treatments for the drop in pH. At some time points the inoculated corn silage would have a greater drop in pH than uninoculated corn silage, and between other time points uninoculated corn silage would have a greater drop. The consistent trend was that the pH was lower at each time point for inoculated corn silage versus uninoculated corn silage (Figure 10).

Regression Analyses
In experiments 1 and 2, the regression relationships among DM content, WSC concentration, temperature, VFA and lactate concentrations, and pH of corn silage were analyzed at 57 d after ensiling. In experiment 2, a combination of DM, lactate, and WSC concentration explained 84% of the variation (P < 0.0001) in pH of corn silage at 57 d after ensiling. However, in experiment 1, DM (16%; P < 0.01), lactate (0%; P = 0.73), and WSC (4%; P = 0.51) concentrations, did not individually explain a large amount of variation in the pH of corn silage at 57 d after ensiling. Acetate concentration explained 65% of the variation (P < 0.0001) in pH of corn silage at 57 d after ensiling, and when lactate, WSC, temperature, and DM content were added to acetate concentration, 86% of the variation (P < 0.01) in pH of corn silage at 57 d after ensiling was explained in experiment 1.

Dry matter content of the corn silage explained 64% of the variation (P < 0.0001) in lactate concentration in corn silage at 57 d after ensiling in experiment 2. Adding both WSC concentration and temperature to DM content to predict lactate concentration did not strengthen the R² to a large extent (67.5%; P < 0.0001). However, in experiment 1, a combination of DM content, temperature, and WSC concentration explained 64% of the variation (P < 0.04) in lactate concentration of corn silage at 57 d after ensiling. These results demonstrate that DM content of the whole corn plant along with the concentrations of WSC, VFA, and lactate affect each other and affect the pH of corn silage.

Dry Matter Recovery
Dry matter recovery 57 d after ensiling ranged between 88 and 100 percent (Table 7). Maturity and processing of corn silage had an effect on DM recovery in experiments 1 and 2 (Table 7). In experiment 1, DM recovery was significantly lower (P < 0.003) for corn silage harvested at a medium maturity (one-third ML; 92.2%) compared with hard dough (94.5%) and two-thirds ML [95.2%; Table 7]. In experiment 2, there was a hybrid x maturity interaction for DM recovery. Hybrid 3845 corn silage harvested at one-third ML (89%) had significantly lower (P < 0.005) DM recovery than corn silage harvested at advanced maturities [two-thirds ML—93.2% and BL—94.7%; experiment 2; Table 7]. Hybrid Quanta corn silage harvested at two-thirds ML (92.4%) had lower (P < 0.09) DM recovery than corn silage harvested at one-third ML (94.8%) and BL (95.4%) maturities (Table 7). The lower DM recovery for hybrid 3845 corn silage harvested at the earliest maturity (one-third ML) in experiment 2 can be partially explained by increased microbial activity (increased lactate and ethanol concentrations and lower pH 57 d after ensiling) compared with advanced maturities (two-thirds ML and BL). However, the response of DM recovery due to corn silage maturity is difficult to explain in experiment 1 and for hybrid Quanta in experiment 2.

The effect of mechanical processing of corn silage on DM recovery differed between experiments (Table 7). In experiment 1, processed corn silage had significantly greater (P < 0.0001) DM recovery 57 d after ensiling than unprocessed corn silage (Table 7). In experiment 2, unprocessed corn silage had significantly greater (P < 0.0009) DM recovery at 57 d after ensiling than processed corn silage (Table 7). The reason for the opposite trend between experiments is unknown. However, it seems that when fermentation was greater (increased temperature and lactate concentration 57 d after ensiling) the DM recovery was lower. The data in this study indicate that all silage went through a rapid and complete fermentation. Therefore, these results suggest that the slight increase in microbial activity (experiment 1 - unprocessed > processed and experiment 2 - processed > unprocessed) tended to decrease DM recovery between processed and unprocessed corn silage in experiments 1 and 2.

	CONCLUSIONS

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 
Many factors of corn silage management affected silage fermentation characteristics and DM recovery in this study. Overall, there tends to be a strong relationship between DM, WSC, lactic and acetic acid concentrations, and the pH level in corn silage by 57 d after ensiling. In experiment 1, a combination of DM content, temperature, WSC, lactate, and acetate explained 86% of the variation in pH of corn silage by 57 d after ensiling. In experiment 2, a combination of DM content, lactate, and WSC concentration explained 84% of the variation in pH of corn silage by 57 d after ensiling.

Maturity at harvest tended to have a greater impact on silage fermentation characteristics of corn silage than mechanical processing and inoculation. In experiments 1 and 2, corn silage harvested at the earliest maturity tended to have decreased DM content and increased WSC concentration during the ensiling process than corn silage harvested at advanced maturities. In experiment 2, pH levels were lower for corn silage harvested at the early maturity (one-third milkline) compared with advanced maturities (two-thirds milkline and blackline) by 57 d after ensiling. The difference in pH among maturities can be explained by the greater concentration of WSC at the early maturity (one-third ML) soon after ensiling (2, 3, 6, and 10 d after ensiling) compared with advanced maturities (two-thirds ML and BL). The increased WSC concentrations in the less mature corn silage provided nutrients for bacteria to grow and produce primarily lactic acid (6, 10, and 57 d after ensiling) and some acetic acid (2, 3, 6, and 10 d after ensiling), which reduced the pH of corn silage more than at the advanced maturities. In experiment 1, the pH of corn silage harvested at the medium maturity tended to be lower than at the other maturities by 57 d after ensiling. This can be partially explained by the greater lactate concentration of corn silage harvested at the medium maturity in the first few d following ensiling (2, 3, 6, and 10 d). The reason for the difference between experiments is unknown, and the corn silage in experiment 2 followed a more classic trend for lactic acid production and pH decline than the corn silage in experiment 1.

Mechanical processing had minimal and inconsistent effects on silage fermentation characteristics in experiments 1 and 2. There was a slight change in silage fermentation when corn silage was inoculated with Pioneer 1132 inoculant in experiment 1. In experiment 2, however, the inoculated and uninoculated corn silage tended to have a similar fermentation profile. In experiment 1, the inoculated corn silage had increased temperature, lactate and acetate concentrations, and lower WSC and pH levels compared with uninoculated corn silage.

Dry matter recovery tended to be greater for processed corn silage in experiment 1, and greater for unprocessed corn silage in experiment 2. However, the reason for the difference between experiments is unknown. It seems that when fermentation was greater (increased temperature and lactate concentration 57 d after ensiling) the dry matter recovery was lower. All of the silage treatments in this study went through a rapid and complete fermentation. Therefore, it appears that when there is a slight increase in microbial activity for a certain silage treatment (such as processed and unprocessed), there is a decrease in silage DM recovered from the silo.

	REFERENCES

TOP ABSTRACT INTRODUCTION MATERIALS AND METHODS RESULTS AND DISCUSSION CONCLUSIONS REFERENCES

 


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