Effect of Ensiling Density on Fermentation Characteristics and Aerobic Stability of Pennisetum giganteum Silages
by
Guofeng Xu
1, 
Feifei Yang
2,
Junfeng Hu
3,
Yanjie Wang
1,
Dong Dong
1,
Zhihao Dong
1,
Junfeng Li
1 and
Tao Shao
1,* 1
Institute of Ensiling and Processing of Grass, College of Agro-Grassland Science, Nanjing Agricultural University, Nanjing 210095, China
2
Lianyungang Biological Engineering Specialized Secondary School, Lianyungang 222000, China
3
Agricultural and Rural Office of Hemudu Town, Ningbo 315414, China
*
Author to whom correspondence should be addressed.
Agronomy 2024, 14(9), 1990; https://doi.org/10.3390/agronomy14091990
Submission received: 22 July 2024
/
Revised: 26 August 2024
/
Accepted: 26 August 2024
/
Published: 2 September 2024
(This article belongs to the Section Agricultural Biosystem and Biological Engineering)
Abstract
:The current work aimed to evaluate the effect of ensiling density on the fermentation quality and aerobic stability of Pennisetum giganteum silages. The silage was ensiled in laboratory silos (1 L), and three treatments were designed according to different ensiling densities: (1) low density (LD, 750 kg/m3); (2) medium density (MD, 900 kg/m3); and (3) high density (HD, 1050 kg/m3). During ensiling, the silage was sampled for a fermentation quality analysis. All silages were well preserved, as indicated by the high lactic acid (LA) content and low pH (<4.2). The MD treatment had the highest acetic acid content (24.9 g/kg dry matter) and the HD treatment had the lowest ammonia nitrogen (NH3-N) content (68.2 g/kg total nitrogen, TN) among all silages after 45 days of ensiling. The aerobic stability of HD, MD, and LD persisted for 51 h, 54 h, and 48 h, respectively. The NH3-N contents of HD and MD were below 80 g/kg TN during aerobic exposure. These results show that the increase in ensiling density improved the fermentation quality and aerobic stability of Pennisetum giganteum silages.
1. Introduction
Pennisetum giganteum belongs to the family Poaceae and genus Pennisetum, and it is suitable for growing in tropical, subtropical, and temperate areas [1]. It is a C4 plant with a high photosynthetic rate, which is characterized by strong regeneration ability and a high biomass, and it is an excellent forage resource. Pennisetum giganteum is widely cultivated in South China, whereas the high temperature and humidity climate characteristics are detrimental to its long-term preservation. Ensiling is an effective method to prolong the preservation of forage; it refers to the anaerobic fermentation process in which lactic acid bacteria (LAB) ferment water-soluble carbohydrate (WSC) to produce organic acids, resulting in a rapid drop in pH and achieving stable silage.
After the raw materials are loaded into the silo, oxygen is inevitably trapped in the sealed silo. The compaction density of the raw materials directly determined the amount of oxygen trapped in the silo, and the oxygen had an adverse effect on the fermentation quality. During the initial aerobic phase in the silo, the respiration of plant cells can decompose organic matter and cause the loss of dry matter (DM), while the metabolism of aerobic microorganisms (e.g., yeast, mold, acetic acid bacteria, etc.) helps them consume nutrients. In addition, the activity of molds produces mycotoxins, which have a potentially harmful effect on animal health and animal by-products [2]. Therefore, the rapid achievement of anaerobic conditions is of great importance to obtain quality silage. In addition, a low ensiling density makes it easy for air to penetrate the silage during aerobic exposure, and the silages will spoil more quickly. The aerobic spoilage of silages is harmful because of the high nutrient losses; therefore, high aerobic stability is necessary to ensure quality silages. Pennisetum giganteum has a porous and stemmy physical structure that makes it difficult to compact, and large amounts of air may remain in the silo. The forage is compacted through the external force in the process of loading, which can increase the ensiling density and promote the exclusion of air. The compaction of raw materials can also promote plant cell breakdown and release plant cell juice, which are conducive to initiate lactic acid (LA) fermentation. However, Pennisetum giganteum has a high moisture content, and overcompaction might easily lead to the loss of juice and clostridium fermentation. Therefore, a suitable compaction density has important significance for silage making.
In a previous work, researchers focused on the effect of the microbial factor on the fermentation quality of Pennisetum giganteum [3]. Information about the effect of ensiling density on the fermentation quality and aerobic stability of Pennisetum giganteum is limited, especially from experiments related to aerobic stability. Thus, this work aimed to evaluate the effect of ensiling density on the fermentation quality and aerobic stability of Pennisetum giganteum silages.
2. Materials and Methods
2.1. Silage Preparation
The experiment was carried out at the Institute of Ensiling and Processing of Grass, Nanjing Agricultural University, China. Pennisetum giganteum was harvested at the vegetative stage from the experimental plot of Nanjing Agricultural University (31°61′ N, 119°18′ E). The chemical compositions and microbial counts of raw material are shown in Table 1. The anaerobic fermentation experiment followed a completely randomized design with a 3 × 6 factorial scheme (3 treatments with 6 silo opening times) with five repetitions. The aerobic test followed a completely randomized design with a 3 × 4 factorial scheme (3 treatments with 4 silo opening times) with five repetitions. Three treatments were designed according to different ensiling densities: (1) low density (LD, 750 kg/m3); (2) medium density (MD, 900 kg/m3); and (3) high density (HD, 1050 kg/m3). The fresh Pennisetum giganteum were chopped into 1–2 cm lengths with a fodder chopper, and then they were placed into the laboratory silo (1 L). The laboratory silo was sealed with screw tops and plastic tape. A total of 135 silos were stored at room temperature, with 90 silos being sampled for fermentation quality analysis and another 45 silos being used for aerobic stability test.
2.2. Chemical Composition and Microbial Count Analysis
The Pennisetum giganteum was analyzed for chemical compositions and microbial counts before ensiling. The Pennisetum giganteum (25 g) was mixed with 250 g deionized water and extracted at 4 °C for 24 h. The aqueous extract was filtered through two layers of gauze, and the aqueous extract was used for determining the buffering capacity of Pennisetum giganteum. Buffering capacity was measured through the method of hydrochloric acid–sodium hydroxide [4].
For sampling, 150 g of sample was oven-dried at 65 °C to a constant weight, and then the dry matter (DM) was measured. The dry sample was ground to pass a 1 mm screen with a laboratory knife mill (FW100, Taisite Instrument Co., Ltd., Tianjin, China). The dry sample power was used for determining total nitrogen (TN) by Kjeldahl method [5]; crude protein content was calculated by TN × 6.25. According to the method of Van Soest, et al. [6], neutral detergent fiber (aNDF) and acid detergent fiber (ADF) were determined. Water-soluble carbohydrate (WSC) was measured by the method of Thomas [7].
The sample (30 g) was mixed with 90 g of deionized water and extracted at 4 °C for 24 h. The aqueous extract was filtered through two layers of gauze and a layer of filter paper. Then, the aqueous extract was used to determine pH. Part of the aqueous extract was taken to determine organic acids and ethanol by Agilent 1260 HPLC system (Agilent Technologies, Inc., Santa Clara, CA, USA) and Carbomix® H-NP5 column (mobile phase, 2.5 mM/L H2SO4; flow rate, 0.5 mL/min; column temperature, 55 °C). Ammonia nitrogen (NH3-N) was measured by phenol-hypochlorite reaction method [8].
The sample (10 g) was mixed with 90 mL 0.85% sterilized saline solution and kept in the orbital shaker (30 °C, 120 rpm) for 1 h; the microbial eluent was serially diluted with 0.85% sterilized saline solution. Lactic acid bacteria (LAB) were counted after anaerobic incubation on deMan, Rogosa, and Sharp agar medium (Shanghai Shengwei Biochemical Technology Co., Ltd., Shanghai, China) for 48 h at 37 °C. Yeasts were counted after aerobic incubation on Potato Dextrose agar medium (Shanghai Shengwei Biochemical Technology Co., Ltd., Shanghai, China) for 48 h at 30 °C. Aerobic bacteria were counted after aerobic incubation on nutrient agar medium (Shanghai Shengwei Biochemical Technology Co., Ltd., Shanghai, China) for 24 h at 37 °C. All microbial data were transformed to log10 for presentation.
2.3. Aerobic Stability Analysis
After ensiling, a total of 45 silos were opened for the aerobic stability test. Each silo was wrapped with two layers of gauze to prevent contamination from dust and then stored at room temperature. The probe of the multichannel temperature recorder (MDL-1048A high-precision temperature recorder, Shanghai Tianhe Automation Instrument Co., Ltd., Shanghai, China) was placed into the center of the silage to record the temperature variation every 30 min. Six probes were placed into the environment to record the room temperature. Aerobic stability is defined as the hour required for the temperature of silage 2 °C above room temperature [9]. After exposure to air, the samples were analyzed for the dynamic change in DM, NH3-N, organic acids, ethanol, and microbial counts at 2, 4, and 6 days.
2.4. Statistical Analysis
The data of chemical compositions, fermentation quality, and microbial counts were analyzed by the general linear model (GLM) procedure with the following model:
where Yijk is the dependent variable; μ is the overall mean; Ti is the fixed effect of treatment; Dj is the fixed effect of day; (T × Dj)ij is the first-order interaction; and eijk is the residual error. Significant differences among means were analyzed by Tukey’s test. Significant differences were declared at p < 0.05. All the above data were analyzed by SAS (version 9.4).
Yijk = μ + Ti + Dj + (Ti × Dj)ij + eijk
3. Results
3.1. Chemical Compositions and Microbial Counts of Pennisetum giganteum
As shown in Table 1, Pennisetum giganteum was harvested at the vegetative stage and had a DM of 199 g/kg fresh weight (FW). The CP and WSC content were 108 g/kg DM and 61.0 g/kg DM, respectively. The buffering capacity of Pennisetum giganteum was 19.6 mEq/kg DM. The initial populations of LAB, yeast, and aerobic bacteria attached to fresh Pennisetum giganteum were 3.08, 5.62, and 4.93 log10 cfu/g FW, respectively.
3.2. Fermentation Quality of Pennisetum giganteum
Ensiling densities and ensiling days significantly (p < 0.05) affected the pH, PA, and ethanol. The LA/AA linearly (p < 0.05) increased, and the pH, PA, and ethanol linearly (p < 0.01) decreased with the increase in ensiling density (Table 2). The pH of HD was significantly (p < 0.05) lower than LD. The AA content of LD peaked at 14 days of ensiling, and the AA contents of MD and HD peaked at 45 days of ensiling. The LD had significantly (p < 0.05) higher PA content relative to HD. There was no significant (p > 0.05) difference in the mean ethanol content among all treatments.
3.3. Chemical Compositions and Microbial Counts of Pennisetum giganteum Silage
The aerobic bacteria count was significantly (p < 0.05) affected by ensiling density, ensiling days, and their interaction (Table 3). With an increase in ensiling density, the DM content linearly (p < 0.001) increased and the NH3-N, yeast, and aerobic bacteria linearly (p < 0.01) decreased. The HD had significantly (p < 0.05) higher DM content compared with MD and LD. The NH3-N content significantly (p < 0.05) increased at the first 14 days of ensiling. The NH3-N content of HD was significantly (p < 0.05) lower than LD. The LAB counts of HD and MD gradually increased within 8 days of ensiling and then continuously decreased until 45 days of ensiling. The LAB count of LD peaked at 14 days of ensiling. The LD had significantly (p < 0.05) higher yeast counts compared to HD and MD. At 4 days of ensiling, the HD and MD had significantly (p < 0.05) lower aerobic bacteria counts than LD.
3.4. Aerobic Stability of Pennisetum giganteum Silage
As shown in Figure 1, the aerobic stability of LD, MD, and HD persisted for 48 h, 54 h, and 51 h, respectively. The pH and AA were significantly (p < 0.05) affected by ensiling density, aerobic exposure days, and their interaction (Table 4). The pH, AA, PA, and ethanol linearly (p < 0.01) decreased with an increase in ensiling density. After 6 days of aerobic exposure, the pH of HD, MD, and LD increased by 0.21, 0.22, and 2.93, respectively. The LD significantly (p < 0.05) increased the pH compared to HD and MD after 2 days of aerobic exposure. The HD and MD significantly (p < 0.05) decreased the contents of AA compared with LD at 6 days of aerobic exposure. Ensiling density, aerobic exposure days, and their interaction significantly (p < 0.01) affected the NH3-N, LAB, and yeast. The DM and aerobic bacteria were mainly (p < 0.001) affected by ensiling density and aerobic exposure days. With an increase in ensiling density, the DM content linearly (p < 0.001) increased and the NH3-N, LAB, yeast, and aerobic bacteria linearly (p < 0.05) decreased. The NH3-N content was also significantly (p < 0.05) affected by ensiling density (Table 5). The NH3-N content of HD and MD peaked at 6 days of aerobic exposure, which was significantly (p < 0.05) lower than the NH3-N content of LD. After 4 days of aerobic exposure, the NH3-N (126.7 g/kg TN) content of LD exceeded 100 g/kg TN. The yeast counts of all silages were > 5.0 log10 cfu/g FW. Moreover, the counts of yeast and aerobic bacteria significantly (p < 0.05) increased during aerobic exposure.
4. Discussion
4.1. Fermentation Quality of Pennisetum giganteum
It is well known that the WSC content is of great importance for silage fermentation. In this work, the Pennisetum giganteum had enough WSC content (61.0 g/kg DM), which met the requirement of WSC content (60–80 g/kg DM) for quality silage making [10]. Furthermore, the low buffering capacity (19.6 mEq/kg DM) contributes to producing quality silages because it promotes a rapid decline in pH. According to the fermentation parameters, all Pennisetum giganteum silages had low pH (<4.2) and NH3-N content (<100 g/kg TN), indicating all silages were preserved well.
At 4 days of ensiling, the pH of silages rapidly dropped below 4.2, which is associated with low buffering capacity. The low buffering capacity requires less acid to reduce the pH below 4.2 [11]. The HD and MD had a lower pH and higher LA content compared with LD; this is probably because the high ensiling density trapped less oxygen in the silo. The oxygen is necessary for the metabolism of aerobic microorganisms, and the volume of oxygen in the silo can affect the survival time of aerobic microorganisms. The high ensiling density likely shortened the initial aerobic phase, which contributed to suppress the growth of aerobic microorganisms and accelerate the proliferation of LAB during the early stage of ensiling. The LAB then ferment sugars into LA, causing the decline in pH. Furthermore, the compaction of silage led to the breakdown of cells and the release of plant juice, which may have promoted LAB fermentation. After 14 days of ensiling, the LA content gradually decreased, which can be explained by some heterofermentative LAB (e.g., Lactobacillus buchneri, etc.) being able to utilize LA as an energy source [12]. The AA content in LD decreased after 14 days of ensiling, which may be related to enterobacteria. The enterobacteria could convert AA to acetoin and butanediol [13]. The ratio of LA/AA increased with the ensiling density, indicating that homolactic fermentation was promoted, and the homolactic fermentation has a high conversion efficiency from WSC to LA [14].
4.2. Chemical Compositions and Microbial Counts of Pennisetum giganteum Silages
The increase in DM content with higher ensiling density indicated that the enhancement of ensiling density reduced DM loss. Muck [15] suggested the DM loss was mainly due to plant respiration, aerobic microorganisms, and clostridia activity. The high ensiling density promoted the exclusion of oxygen from the silo, allowing the silo to achieve anaerobic conditions more quickly. Therefore, the DM loss caused by plant respiration and aerobic microorganisms was reduced. The NH3-N content continuously increased within 14 days of ensiling, which was mainly related to the hydrolysis of protein. The main factors of proteolysis are plant protease and microbial activity [16]. The initial proteolysis was caused by plant protease, and the subsequent conversion of free amino acids to NH3-N was dominated by microorganisms [17]. The NH3-N content of HD was lower than LD; this was probably because of the rapid rate of pH decline. The HD had a faster rate of pH decline, which is important to limit the proteolysis [18]. The LD had a high NH3-N content (101 g/kg TN) at 14 days of ensiling, which exceeded the maximum acceptable level (<100 g/kg TN) of quality silage. This was probably because the high moisture content (>800 g/kg FW) could enhance the risk of extensive proteolysis [19]. After 14 days of ensiling, the LAB count showed a downward trend, which could be explained by the low pH suppressing the growth of LAB [20]. After 45 days of ensiling, the counts of yeast remained relatively high (>7 log10 cfu/g FW); this is probably because the yeast was inhibited rather than killed during ensiling. At 4 days of ensiling, the aerobic bacteria count of HD and MD was significantly lower than LD, indicating the aerobic bacteria was inhibited quickly in HD and MD. This was mainly related to the low oxygen content in HD and MD, which limited the survival of aerobic bacteria.
4.3. Aerobic Stability of Pennisetum giganteum Silage
During feed-out, the silage is exposed to air and the aerobic microorganisms proliferate rapidly. The aerobic microorganisms utilize the LA, AA, and WSC as energy to produce carbon dioxide, water, and heat during aerobic exposure [13], resulting in the spoilage of silages. The aerobic spoilage not only causes the DM and nutrient loss but also has adverse effects on animal performance and health [21]. Therefore, inhibiting aerobic spoilage in the silo is essential for preventing nutrient loss and ensuring feed safety. To monitor the aerobic spoilage of silages, temperature fluctuation is used as an indicator of aerobic spoilage. In this work, a difference in the duration of aerobic stability among different ensiling densities was observed. The aerobic stability of HD, MD, and LD was 51 h, 54 h, and 48 h, respectively. The HD and MD showed increased aerobic stability compared with LD, indicating that the increase in ensiling density contributed to enhancing the aerobic stability. The MD had the highest aerobic stability, which might be attributed to the high AA content. The lipophilic, undissociated acetic acid molecules can penetrate the bacterial plasma membrane and interfere with the metabolism of microorganisms [22], thereby suppressing the growth of undesirable microorganisms and improving the aerobic stability. Moreover, the high ensiling density restricted oxygen entering in silages and inhibited the activity of aerobic microorganisms.
The stable pH directly reflected that all silages maintained high aerobic stability at the first 2 days of aerobic exposure. The LA content of LD showed a rapid decrease and the pH significantly increased after 2 days of aerobic exposure, which might be related to the proliferation of lactate-assimilating yeast and LAB. Woolford [23] and Nishino, et al. [24] reported that lactate-assimilating yeast and some LAB species could utilize LA as energy. The ethanol content of HD and MD declined gradually, in association with its volatility and utilization by acetic acid bacteria [25]. At the first 2 days of aerobic exposure, the NH3-N content of all silages showed no remarkable change; this was probably because the low pH (<3.9) prevented the proteolysis caused by plant protease and proteolytic microorganisms. The NH3-N contents of HD and MD were below 80 g/kg TN during aerobic exposure, whereas the NH3-N content of LD reached 127 g/kg TN after 4 days of aerobic exposure. This might be related to the sharp increase in pH in LD, which could weaken the inhibitory effect on plant proteases and proteolytic microorganisms.
At the beginning of aerobic exposure, the yeast counts were above 105 log10 cfu/g, which is considered prone to aerobic spoilage [26]. However, all silages had a high aerobic stability within 48 h, as indicated by the temperature fluctuation. The authors of [23] suggested the lactate-assimilating yeast decided whether the silage would spoil or not; the 105 log10 cfu/g figure was valid only if it contained yeast of this type. In this work, the increase in ensiling density affected the AA content and the penetration of oxygen in silages, which might be the primary factors to improve the aerobic stability of silages.
5. Conclusions
The current work showed that all silages were well preserved after 45 days of ensiling. However, the high ensiling density facilitated the rapid reduction in pH during the early stage of ensiling, which effectively reduced the loss of DM and nutrients. The aerobic stability of HD, MD, and LD reached 51 h, 54 h, and 48 h, respectively. Therefore, the increase in ensiling density is of great importance to improve the fermentation quality and aerobic stability. In a word, the medium density is suitable for Pennisetum giganteum silage making.
Author Contributions
T.S. conceived and designed the study. G.X., F.Y., J.H., Y.W. and D.D. conducted data gathering. G.X., Z.D. and J.L. performed statistical analyses. G.X. and T.S. wrote the article. T.S. was responsible for funding acquisition and supervision of graduate students. All authors have read and agreed to the published version of the manuscript.
Funding
Demonstration of Ecological Grass Husbandry Technology in Tibet High-cold Region, Grant/Award Number: XZ202301YD0012C; Major Science and Technology Special Project of Tibet-Technology Mode Innovation and Demonstration of Spatio-temporal Expansion of Tibet Prataculture, Grant/Award Number: XZ202101ZD0003N.
Data Availability Statement
Data are contained within the article. The data presented in this study are available in the article.
Conflicts of Interest
The authors declare there are no conflicts of interest.
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Figure 1.
Effect of different ensiling densities on aerobic stability of Pennisetum giganteum silage (bars indicate standard errors of the means): LD, low density (750 kg/m3); MD, medium density (900 kg/m3); HD, high density (1050 kg/m3). Different letters (a–c) represent significant difference (p < 0.05).
Figure 1.
Effect of different ensiling densities on aerobic stability of Pennisetum giganteum silage (bars indicate standard errors of the means): LD, low density (750 kg/m3); MD, medium density (900 kg/m3); HD, high density (1050 kg/m3). Different letters (a–c) represent significant difference (p < 0.05).
Table 1.
Chemical and microbial compositions of Pennisetum giganteum before ensiling.
| Items 1 | Pennisetum giganteum 2 |
|---|---|
| Chemical compositions | |
| DM (g/kg FW) | 199 ± 15.25 |
| CP (g/kg DM) | 108 ± 6.76 |
| aNDF (g/kg DM) | 586 ± 16.80 |
| ADF (g/kg DM) | 324 ± 8.52 |
| Hemicellulose (g/kg DM) | 262 ± 10.49 |
| WSC (g/kg DM) | 61.0 ± 8.14 |
| pH | 5.85 ± 0.14 |
| Buffering capacity (mEq/kg DM) | 19.6 ± 2.48 |
| Microbial compositions | |
| LAB (log10 cfu/g FW) | 3.08 ± 0.30 |
| Yeast (log10 cfu/g FW) | 5.62 ± 0.47 |
| Aerobic bacteria (log10 cfu/g FW) | 4.93 ± 0.43 |
1 DM, dry matter; FW, fresh weight; CP, crude protein; aNDF, neutral detergent fiber (with heat-stable amylase and expressed inclusion of residue ash); ADF, acid detergent fiber; WSC, water-soluble carbohydrate; LAB, lactic acid bacteria. 2 ±, standard deviation.
Table 2.
Effect of different ensiling densities on the fermentation quality of Pennisetum giganteum during ensiling.
Table 2.
Effect of different ensiling densities on the fermentation quality of Pennisetum giganteum during ensiling.
| Items 1 | Treatments 2 | Ensiling Days | Means | SEM 3 | p-Value 4 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4 | 6 | 8 | 14 | 30 | 45 | T | D | T × D | T-L | T-Q | ||||
| pH | LD | 4.15 Aa | 3.94 Aa | 3.79 ab | 3.34 b | 3.74 ab | 3.74 ab | 3.78 A | 0.030 | <0.001 | <0.001 | 0.188 | <0.001 | 0.113 |
| MD | 3.81 Ba | 3.70 ABa | 3.69 a | 3.18 b | 3.63 a | 3.63 a | 3.61 AB | |||||||
| HD | 3.67 Ba | 3.50 Ba | 3.69 a | 3.22 b | 3.62 a | 3.62 a | 3.55 B | |||||||
| LA (g/kg DM) | LD | 22.8 Bb | 25.5 b | 39.3 ab | 50.8 a | 30.2 b | 35.4 ab | 34.0 | 2.452 | 0.361 | 0.001 | 0.933 | 0.216 | 0.482 |
| MD | 22.7 B | 27.4 | 31.6 | 44.6 | 34.4 | 43.6 | 34.1 | |||||||
| HD | 34.0 A | 32.6 | 35.0 | 58.9 | 33.4 | 39.8 | 39.0 | |||||||
| AA (g/kg DM) | LD | 14.1 b | 14.0 b | 18.6 ab | 23.8 a | 19.5 ab | 18.8 ab | 18.1 | 0.601 | 0.316 | <0.001 | 0.123 | 0.132 | 0.929 |
| MD | 11.9 b | 13.8 b | 16.4 b | 18.1 b | 18.3 ab | 24.9 a | 17.2 | |||||||
| HD | 15.1 | 15.7 | 16.0 | 17.8 | 17.7 | 18.9 | 16.5 | |||||||
| LA/AA | LD | 1.62 B | 1.83 | 2.07 | 2.14 | 1.62 | 1.93 | 1.87 B | 0.056 | 0.001 | 0.072 | 0.939 | <0.001 | 0.235 |
| MD | 1.9 AB | 1.98 | 1.94 | 2.42 | 1.88 | 1.71 | 1.97 B | |||||||
| HD | 2.29 A | 2.39 | 2.25 | 2.61 | 2.28 | 2.12 | 2.32 A | |||||||
| PA (g/kg DM) | LD | 8.72 A | 7.61 | 7.94 | 9.33 | 8.68 | 9.11 | 8.57 A | 0.105 | 0.002 | <0.001 | 0.319 | <0.001 | 0.302 |
| MD | 7.81 Bab | 7.39 b | 8.50 ab | 8.55 ab | 9.17 a | 8.93 a | 8.39 AB | |||||||
| HD | 7.56 B | 7.43 | 7.81 | 8.06 | 7.95 | 8.39 | 7.87 B | |||||||
| Ethanol (g/kg DM) | LD | 11.1 Aab | 10.1 b | 11.1 ab | 16.9 Aab | 11.3 ab | 17.5 a | 13.0 | 0.424 | 0.034 | <0.001 | 0.686 | 0.010 | 0.980 |
| MD | 10.21 AB | 10.1 | 11.0 | 12.4 B | 12.2 | 15.2 | 11.9 | |||||||
| HD | 9.75 B | 9.92 | 10.1 | 11.1 B | 10.1 | 13.6 | 10.7 | |||||||
1 DM, dry matter; LA, lactic acid; AA, acetic acid; LA/AA, lactic acid/acetic acid; PA, propionic acid. 2 LD, low density (750 kg/m3); MD, medium density (900 kg/m3); HD, high density (1050 kg/m3). 3 SEM, standard error of the mean. 4 T, treatment; D, ensiling days; T × D, treatment × ensiling days; T-L, linear effect of ensiling density; T-Q, quadratic effect of ensiling density. Values in the same row (a,b) with different superscript letters are different (p < 0.05); values in the same column (A,B) with different superscript letters are different (p < 0.05).
Table 3.
Effect of different ensiling density on chemical compositions and microbial counts of Pennisetum giganteum silage during ensiling.
Table 3.
Effect of different ensiling density on chemical compositions and microbial counts of Pennisetum giganteum silage during ensiling.
| Items 1 | Treatments 2 | Ensiling Days | Means | SEM 3 | p-Value 4 | |||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 4 | 6 | 8 | 14 | 30 | 45 | T | D | T × D | T-L | T-Q | ||||
| DM (g/kg FW) | LD | 181 B | 206 | 188 | 174 B | 187 | 180 | 186 B | 2.029 | <0.001 | 0.018 | 0.630 | <0.001 | 0.055 |
| MD | 196 A | 206 | 188 | 188 AB | 175 | 183 | 189 B | |||||||
| HD | 209 A | 213 | 209 | 209 A | 206 | 198 | 207 A | |||||||
| WSC (g/kg DM) | LD | 39.0 | 29.7 | 26.3 | 27.7 | 30.2 | 27.2 | 30.0 A | 0.996 | 0.788 | <0.001 | 0.952 | 0.645 | 0.611 |
| MD | 43.06 a | 28.2 b | 26.1 b | 28.9 b | 32.5 b | 29.1 b | 31.3 A | |||||||
| HD | 41.73 a | 33.2 ab | 21.2 b | 29.0 ab | 30.7 ab | 29.5 b | 30.9 A | |||||||
| NH3-N (g/kg TN) | LD | 46.2 c | 62.4 abc | 53.9 bc | 101 Aa | 96.0 ab | 76.8 abc | 72.8 A | 2.608 | <0.001 | <0.001 | 0.227 | <0.001 | 0.744 |
| MD | 49.1 c | 51.2 bc | 57.0 abc | 76.3 Ba | 73.9 ab | 69.9 abc | 62.9 AB | |||||||
| HD | 43.3 b | 49.3 ab | 45.7 b | 66.0 Ba | 59.3 ab | 68.2 a | 55.3 B | |||||||
| LAB (log10 cfu/g FW) | LD | 7.00 c | 8.03 b | 8.97 Ba | 9.11 a | 8.38 ab | 8.53 Aab | 8.34 | 0.104 | 0.080 | <0.001 | 0.003 | 0.129 | 0.092 |
| MD | 7.39 c | 8.51 b | 9.60 Aa | 9.44 a | 8.41 b | 8.03 Bb | 8.56 | |||||||
| HD | 7.75 c | 8.66 abc | 9.51 Aa | 9.05 ab | 8.24 bc | 7.74 Cc | 8.49 | |||||||
| Yeast (log10 cfu/g FW) | LD | 7.03 Ad | 9.23 Aa | 8.73 Aab | 8.59 Abc | 8.32 Abc | 8.03 Ac | 8.32 A | 0.096 | <0.001 | <0.001 | 0.415 | <0.001 | 0.197 |
| MD | 6.78 ABb | 8.46 Ba | 8.12 ABa | 7.76 ABa | 7.90 ABa | 7.78 ABa | 7.80 B | |||||||
| HD | 6.45 Bb | 7.96 Ba | 7.72 Ba | 7.68 Ba | 7.60 Ba | 7.45 Ba | 7.48 B | |||||||
| Aerobic bacteria (log10 cfu/g FW) | LD | 9.63 Aa | 8.64 ab | 8.27 b | 8.35 b | 7.70 b | 7.87 ABb | 8.41 | 0.915 | 0.017 | <0.001 | 0.043 | 0.006 | 0.470 |
| MD | 8.86 Ba | 8.53 ab | 8.33 ab | 8.31 ab | 7.73 b | 8.10 Aab | 8.31 | |||||||
| HD | 8.84 Ba | 8.78 a | 8.39 a | 8.13 ab | 7.23 bc | 7.01 Bc | 8.06 | |||||||
1 DM, dry matter; FW, fresh weight; NH3-N, ammonia nitrogen; TN, total nitrogen; WSC, water soluble carbohydrate; LAB lactic acid bacteria. 2 LD, low density (750 kg/m3); MD, medium density (900 kg/m3); HD, high density (1050 kg/m3). 3 SEM, standard error of the mean. 4 T, treatment; D, ensiling days; T × D, treatment × ensiling days; T-L, linear effect of ensiling density; T-Q, quadratic effect of ensiling density. Values in the same row (a–c) with different superscript letters are different (p < 0.05); values in the same column (A–C) with different superscript letters are different (p < 0.05).
Table 4.
Effect of different ensiling densities on fermentation parameters of Pennisetum giganteum silage during aerobic exposure.
Table 4.
Effect of different ensiling densities on fermentation parameters of Pennisetum giganteum silage during aerobic exposure.
| Items 1 | Treatments 2 | Aerobic Exposure Days | Means | SEM 3 | p-Value 4 | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 2 | 4 | 6 | T | D | T × D | T-L | T-Q | ||||
| pH | LD | 3.74 c | 3.82 Ac | 4.45 Ab | 6.69 Aa | 4.67 A | 0.142 | <0.001 | <0.001 | <0.001 | <0.001 | 0.100 |
| MD | 3.63 b | 3.56 Bb | 3.77 Bab | 3.94 Ba | 3.73 B | |||||||
| HD | 3.62 ab | 3.58 Bb | 3.78 Ba | 3.80 Bab | 3.70 B | |||||||
| LA (g/kg DM) | LD | 35.4 ab | 47.8 Aa | 36.4 ab | 23.3 b | 35.7 | 1.619 | 0.748 | 0.081 | 0.055 | 0.454 | 0.930 |
| MD | 43.6 a | 28.0 Bab | 35.4 ab | 29.5 b | 34.1 | |||||||
| HD | 39.8 | 29.0 B | 30.1 | 33.5 | 33.1 | |||||||
| AA (g/kg DM) | LD | 18.8 | 22.6 A | 23.8 A | 15.6 A | 20.2 A | 0.959 | <0.001 | <0.001 | 0.004 | <0.001 | 0.423 |
| MD | 24.9 a | 22.5 Aab | 16.7 ABbc | 12.7 Bc | 19.2 AB | |||||||
| HD | 18.8 a | 14.6 Bb | 14.5 Bb | 12.2 Bb | 15.0 B | |||||||
| PA (g/kg DM) | LD | 9.11 | 9.68 A | 10.4 | 9.13 A | 9.57 A | 0.197 | <0.001 | 0.558 | 0.218 | <0.001 | 0.134 |
| MD | 8.93 a | 8.00 Bab | 7.63 b | 8.47 Bab | 8.26 B | |||||||
| HD | 8.40 a | 6.98 Cb | 8.24 a | 8.31 Ba | 8.00 B | |||||||
| Ethanol (g/kg DM) | LD | 17.5 a | 23.1 Aab | 12.9 b | 11.3 Ab | 16.2 A | 0.777 | 0.006 | 0.001 | 0.217 | 0.002 | 0.379 |
| MD | 15.2 | 15.4 AB | 10.1 | 10.4 B | 12.8 AB | |||||||
| HD | 13.6 | 11.7 B | 10.6 | 10.2 B | 11.5 B | |||||||
1 DM, dry matter; LA, lactic acid; AA, acetic acid; PA, propionic acid. 2 LD, low density (750 kg/m3); MD, medium density (900 kg/m3); HD, high density (1050 kg/m3). 3 SEM, standard error of the mean. 4 T, treatment; D, ensiling days; T × D, treatment × ensiling days; T-L, linear effect of ensiling density; T-Q, quadratic effect of ensiling density. Values in the same row (a–c) with different superscript letters are different (p < 0.05); values in the same column (A–C) with different superscript letters are different (p < 0.05).
Table 5.
Effect of different ensiling densities on chemical compositions and microbial counts of Pennisetum giganteum silage during aerobic exposure.
Table 5.
Effect of different ensiling densities on chemical compositions and microbial counts of Pennisetum giganteum silage during aerobic exposure.
| Items 1 | Treatments 2 | Aerobic Exposure Days | Means | SEM 3 | p-Value 4 | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| 0 | 2 | 4 | 6 | T | D | T × D | T-L | T-Q | ||||
| DM (g/kg FW) | LD | 180 | 180 | 192 B | 201 | 188 B | 2.346 | <0.001 | <0.001 | 0.833 | <0.001 | 0.244 |
| MD | 183 | 192 | 195 AB | 205 | 194 B | |||||||
| HD | 198 b | 201 b | 203 Ab | 224 a | 207 A | |||||||
| NH3-N (g/kg TN) | LD | 75.8 c | 89.3 Ac | 127 Ab | 181 Aa | 119 A | 6.285 | <0.001 | <0.001 | <0.001 | <0.001 | <0.001 |
| MD | 69.9 ab | 59.6 Bab | 50.2 Bb | 79.0 Ba | 64.7 B | |||||||
| HD | 68.2 b | 63.0 Bb | 59.0 Bb | 75.6 Ba | 66.4 B | |||||||
| LAB (log10 cfu/g FW) | LD | 8.53 Ac | 9.85 Ab | 10.9 Aa | 11.1 Aa | 10.1 A | 0.187 | <0.001 | <0.001 | 0.005 | <0.001 | 0.397 |
| MD | 8.03 Bc | 8.86 Bb | 10.2 Ba | 10.8 Aa | 9.49 AB | |||||||
| HD | 7.74 Cc | 8.72 Bb | 9.88 Ba | 9.70 Ba | 9.01 B | |||||||
| Yeast (log10 cfu/g FW) | LD | 8.03 Ad | 8.79 c | 10.1 Ab | 10.8 Aa | 9.43 | 0.174 | <0.001 | <0.001 | 0.004 | <0.001 | 0.147 |
| MD | 7.78 ABd | 8.47 c | 9.16 Bb | 10.5 Aa | 8.96 | |||||||
| HD | 7.45 Bc | 8.68 b | 9.04 Bb | 9.77 Ba | 8.74 | |||||||
| Aerobic bacteria (log10 cfu/g FW) | LD | 7.87 ABb | 8.94 b | 11.8 Aa | 11.5 a | 10.0 | 0.282 | <0.001 | <0.001 | 0.542 | <0.001 | 0.785 |
| MD | 8.10 Ab | 8.38 b | 11.0 Ba | 11.1 a | 9.64 | |||||||
| HD | 7.01 Bc | 8.09 b | 10.9 Ba | 10.6 a | 9.15 | |||||||
1 DM, dry matter; FW, fresh weight; NH3-N, ammonia nitrogen; TN, total nitrogen; WSC, water soluble carbohydrate; LAB lactic acid bacteria. 2 LD, low density (750 kg/m3); MD, medium density (900 kg/m3); HD, high density (1050 kg/m3). 3 SEM, standard error of the mean. 4 T, treatment; D, ensiling days; T × D, treatment × ensiling days; T-L, linear effect of ensiling density; T-Q, quadratic effect of ensiling density. Values in the same row (a–d) with different superscript letters are different (p < 0.05); values in the same column (A–C) with different superscript letters are different.
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MDPI and ACS Style
Xu, G.; Yang, F.; Hu, J.; Wang, Y.; Dong, D.; Dong, Z.; Li, J.; Shao, T. Effect of Ensiling Density on Fermentation Characteristics and Aerobic Stability of Pennisetum giganteum Silages. Agronomy 2024, 14, 1990. https://doi.org/10.3390/agronomy14091990
AMA Style
Xu G, Yang F, Hu J, Wang Y, Dong D, Dong Z, Li J, Shao T. Effect of Ensiling Density on Fermentation Characteristics and Aerobic Stability of Pennisetum giganteum Silages. Agronomy. 2024; 14(9):1990. https://doi.org/10.3390/agronomy14091990
Chicago/Turabian StyleXu, Guofeng, Feifei Yang, Junfeng Hu, Yanjie Wang, Dong Dong, Zhihao Dong, Junfeng Li, and Tao Shao. 2024. "Effect of Ensiling Density on Fermentation Characteristics and Aerobic Stability of Pennisetum giganteum Silages" Agronomy 14, no. 9: 1990. https://doi.org/10.3390/agronomy14091990
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