3. Ensiling process

Ensiling is a method of forage conservation. It is based on natural fermentation, in which lactic bacteria convert the WSC into organic acids (principally lactic acid) under anaerobic conditions. As a result pH decrease and the silage is preserve [17]. The primordial objective of forage ensiling is to preserve the original composition of nutrients found in natural plant during storage with minimum losses [18].

The forage conservation as silage depend on favorable conditions, such as the amount sufficient WSC to lactic acid production and low buffering capacity, which promote rapid lowering of pH that inhibits the growth of some deleterious microorganisms, maintaining the nutritional values of forage.

Before the ensiling process, aerobic and facultative anaerobic microorganisms are able to grow in high pH and predominance. As long as pH decrease and oxygen is consumed, the anaerobic and anaerobic facultative acid tolerant bacteria grow in the environment.

Ensiling is divided into four phases with different time and intensity [19, 20].

The C4 plants are considered to be dominant in resistance and drought tolerance because they are capable of maintaining photosynthesis with closed stomata. Even with the small reduction of photosynthesis under water stress conditions, the C4 crops such as sorghum and panicum have the ability to grow in dry region and are considered to have a great potential for enhancing forage production and food security in the world [7]. The C4 plants provide competitive conditions of low availability of water, high temperatures, and high light intensities [10]; they have high water-use efficiency and mechanisms for CO2 concentration [7].

Other factor that influences the nature of response of plants to drought is the thermal stress. Thermal stress can reduce transpiration and can dehydrate the plant cells, reduce the availability of nutrients, and cause osmotic stress together with the drought. In the plant growth stage, water stress can interfere with the final yield production of the crop [7]. Corn yield, for example, is a culture that is extremely sensitive to water stress during the period of the previous life cycle of flowering. Crops such as sugarcane may have a greater impact of water stress when its leaves

The adaptive responses are based on complex changes to cope with stress, primarily to maintain water potential in main tissues. Crops such as sorghum and pearl millet are drought tolerant and cultivated on a large scale in the semiarid region. These crops are able to maintain photosynthetic activity under water stress conditions and thus increase the final yield [12].

The osmotic adjustment required for drought tolerance forage can increase the solute values as

The concentration of water-soluble carbohydrates (WSC) in ensiled materials influences the fermentation profile because the WSC concentrations are used for the production of lactic acid [13]. The minimum content of WSC to appropriate fermentation of good silage varies between 6 and 12% [14]. In contrast, a large amount of WSC concentration may predispose to undesirable occurrence of fermentation realized from yeasts because of the excessive lactic acid

In the semiarid region, there is a tendency that the forage contains a higher WSC content. The forage sorghum, pearl millet, and buffel grass show a WSC concentration (DM basis) of 13–20,

Ensiling is a method of forage conservation. It is based on natural fermentation, in which lactic bacteria convert the WSC into organic acids (principally lactic acid) under anaerobic conditions. As a result pH decrease and the silage is preserve [17]. The primordial objective of forage ensiling is to preserve the original composition of nutrients found in natural plant during

The forage conservation as silage depend on favorable conditions, such as the amount sufficient WSC to lactic acid production and low buffering capacity, which promote rapid lowering

are establish than in the initial period, which may affect the final yield [7, 11].

fructan [4, 8] increases the values of soluble carbohydrate in these forage.

production, which leads to losses resulting from the alcoholic fermentation [15].

9, and 3.1%, respectively [16].

68 Advances in Silage Production and Utilization

storage with minimum losses [18].

3. Ensiling process

• Aerobic phase: It occurs during filling of silo and extends until a few hours after the packing of silo. The aerobic phase is undesirable because all obligatory and facultative aerobic microorganisms (yeasts, molds, and bacteria) are active in this phase, but it is an inevitable phase. As it is associated with the fermentable substrate and energy losses, it is important to reduce the duration of this phase. It recommended that the forage be chopped, compacted, and rapid packing of the silo [13]. The final stage of the phase includes exhaustion of oxygen in silo.

• Active fermentation phase: After exhaustion of oxygen in silo, there is a decrease in silage pH because of organic acids production from WSC. In initial, enterobacteria and heterofermentative lactic bacteria grow in ensiled mass. With the larger decline of pH, homofermentative lactic bacteria dominate the anaerobic environment. In this phase, there is the more production of organic acid, such as acetic and lactic acids, and also ethanol and CO2. The major growth of lactic acid bacteria (LAB), and consequently, larger lactic acid formation inhibit the development of other microorganisms, principally due to lowering of pH. This phase extends to the stability and reduces excessive microbial activity.

• Stability phase: It a phase with low biologic activity, since it does not penetrate air in the ensiled mass. The pH permanence is stable in 3.8–4.2, inhibiting microbial activity. Only some acid tolerant enzymes maintain activity [20]. The acid pH and anaerobic conditions maintain the ensiled mass stability to the silo opening.

• Discharge phase: It occurs at the opening of the silo and expose the ensiled mass to high oxygen concentration, which favors the growth of enterobacteria, molds, yeasts, and other microorganisms. Yeasts are the first microorganism to develop in silage after the opening, causing deterioration of the conserved forage [13]. There are heat and CO2 production due respiration, which results the decrease in lactic acid and residual WSC, and increase in silage pH [13]. The appropriate management may minimize the losses after opening of silo.

#### 3.1. Microorganism involved in the ensiling process

The ensiling process is complex and variable. It consists, basically, in conjunct action of the large number of microorganisms and may be considered a metabiose because it occurs at simultaneous and successive development of different microorganisms that depends on specific pH, substrates, and potential redox in environment of silo.

The microorganisms present in plant before ensiling may be aerobic and anaerobic, desirable and undesirable to fermentation. Table 1 presents the most common types of microorganisms and their presence in plants.


plant leads to the formation of acid silage due to excessive lactic acid production. Acid silage, such as sugarcane and saccharine sorghum silages, has high ethanol concentration because of

Ensiling of Forage Crops in Semiarid Regions http://dx.doi.org/10.5772/101990 71

The dry matter content is an important factor that affects the fermentation and preservation of ensiled mass. The ideal DM content is between 30 and 35% [13]. However, research studies indicated the values to corn silage being necessary attempt to characteristics of each culture, because it might occur good fermentative profile in silage of forage with inferior DM values. Generally, the high content of moisture favors undesirable microorganisms, such as Clostridium and enterobacteria that are butyric and acetic acid and ammonia producers, implying in nutrient losses. However, higher DM content impacts the compaction and reduction of air

The WSC concentration in ensiled materials influences the fermentative profile, because the WSC concentrations are used for the production of lactic acid [13]. The minimum content of WSC required for appropriate fermentation of good silage varies between 6 and 12% [14].

Other important factors that influence the silage are the buffering capacity that is resistance to lowering the pH of ensiled materials. The compounds able of buffering the environment in forage are some organics acid, potassium, and calcium inorganic bases and nitrogen substances, such as protein and products of their degradation, free amino acids, amine, and ammonia [22]. The action of buffering capacity in silage is associated with other factors such as WSC and DM concentration. Thus, the pH of silage is determined by relationship of protein

The ensiling process changes the natural structure of forage and may cause some losses. Besides the natural physical losses, such as crop losses, chemical losses also occur and may compromise the energy and nutritive value of silage. Although some losses may be

Process Losses (%) Causative agents Classification Respiration 1–2 Plant enzymes Inevitable Fermentation 2–4 Microorganisms Inevitable Effluent 5–7 Moisture Inevitable Secondary fermentation 0–5 Plant, moisture, silo environment Preventable Aerobic deterioration in storage 0–10 Ensiling time, density, plant, packing Preventable Aerobic deterioration in discharge 0–15 Moisture, season, density, technical Preventable

alcoholic fermentation.

present [21].

3.2. Characteristics of forage to ensiling

and water-soluble carbohydrate [22].

Total losses 8–43

Source: Adapted from McDonald et al. [13].

Table 3. Losses in the ensiling process.

3.3. Fermentation loss in the ensiling process

Source: Adapted from Pahlow et al. [20].

Table 1. Typical bacterial and fungal population of plants groups before ensiling.


Source: Adapted from de McDonald et al. [13].

Table 2. Acidify efficiency and fermentation and main fermentative routes of microorganisms in silage.

The microorganisms present in plants are diverse in genera and species with different fermentative routes. Each group has specific temperature and substrate to grow with higher or lower energy demand. In the fermentation process, microorganisms convert soluble substrates into organic compounds. Table 2 presents the main fermentative routes of microorganism in silage.

The growth of lactic acid bacteria in ensiled mass is important because its metabolism does not result in considerable DM losses, following the principle of forage preservation. The LAB converts one mole of glucose to two moles of lactic acid without DM losses [13].

In situations where the forage has a low amount of substrates may have predominant of other microorganisms, such as enterobacteria, because the pH is not low sufficiently. In the opposite situation, ensiling of forage with excess WSC may be in the presence of acid tolerant microorganisms such as yeasts that are able to consume lactic acid and WSC. The excess WSC in the plant leads to the formation of acid silage due to excessive lactic acid production. Acid silage, such as sugarcane and saccharine sorghum silages, has high ethanol concentration because of alcoholic fermentation.

#### 3.2. Characteristics of forage to ensiling

The dry matter content is an important factor that affects the fermentation and preservation of ensiled mass. The ideal DM content is between 30 and 35% [13]. However, research studies indicated the values to corn silage being necessary attempt to characteristics of each culture, because it might occur good fermentative profile in silage of forage with inferior DM values.

Generally, the high content of moisture favors undesirable microorganisms, such as Clostridium and enterobacteria that are butyric and acetic acid and ammonia producers, implying in nutrient losses. However, higher DM content impacts the compaction and reduction of air present [21].

The WSC concentration in ensiled materials influences the fermentative profile, because the WSC concentrations are used for the production of lactic acid [13]. The minimum content of WSC required for appropriate fermentation of good silage varies between 6 and 12% [14].

Other important factors that influence the silage are the buffering capacity that is resistance to lowering the pH of ensiled materials. The compounds able of buffering the environment in forage are some organics acid, potassium, and calcium inorganic bases and nitrogen substances, such as protein and products of their degradation, free amino acids, amine, and ammonia [22]. The action of buffering capacity in silage is associated with other factors such as WSC and DM concentration. Thus, the pH of silage is determined by relationship of protein and water-soluble carbohydrate [22].

#### 3.3. Fermentation loss in the ensiling process

The ensiling process changes the natural structure of forage and may cause some losses. Besides the natural physical losses, such as crop losses, chemical losses also occur and may compromise the energy and nutritive value of silage. Although some losses may be


Source: Adapted from McDonald et al. [13].

Table 3. Losses in the ensiling process.

The microorganisms present in plants are diverse in genera and species with different fermentative routes. Each group has specific temperature and substrate to grow with higher or lower energy demand. In the fermentation process, microorganisms convert soluble substrates into organic compounds. Table 2 presents the main fermentative routes of microorganism in silage. The growth of lactic acid bacteria in ensiled mass is important because its metabolism does not result in considerable DM losses, following the principle of forage preservation. The LAB

LAB Homofermentative Glucose 2 Lactate 96.9 100 LAB Heterofermentative Glucose 1 Lactate + 1 Acetate + CO2 79.6 83 LAB Heterofermentative Glucose 1 Lactate + 1 Ethanol + CO2 97.2 83 Yeast Glucose 2 Ethanol + 2 CO2 97.4 51 Clostridia Glucose 1 Butyrate + 2 CO2 77.9 66 Enterobacteria 2 Glucose 1 Lactate + 1 Acetate(1 Ethanol) + CO2 88.9 83

Recuperation (%)

Energy DM

In situations where the forage has a low amount of substrates may have predominant of other microorganisms, such as enterobacteria, because the pH is not low sufficiently. In the opposite situation, ensiling of forage with excess WSC may be in the presence of acid tolerant microorganisms such as yeasts that are able to consume lactic acid and WSC. The excess WSC in the

converts one mole of glucose to two moles of lactic acid without DM losses [13].

Table 2. Acidify efficiency and fermentation and main fermentative routes of microorganisms in silage.

Groups pH

Table 1. Typical bacterial and fungal population of plants groups before ensiling.

Organism Rota Substrate Product

Source: Adapted from Pahlow et al. [20].

70 Advances in Silage Production and Utilization

Source: Adapted from de McDonald et al. [13].

Total aerobic bacteria >10,000,000 Lactic acid bacteria 10–1,000,000 Enterobacteria 1000–1,000,000 Yeasts 1000–100,000 Molds 1000–10,000 Clostridia 100–1000 Bacillus 100–1000 Acetic acid–producing bacteria 100–1000 Propionic acid–producing bacteria 10–1000

unavoidable, such as biochemist changes, plant respiration, and fermentation (Table 3), other types of losses can be avoided with appropriate practice of the ensiling procedures.

In the case of semiarid, plant species resistance to hydric deficit and climatic conditions are indicated to ensiling. The main forages are sorghum, pearl millet, tropical grasses, leguminous,

Ensiling of Forage Crops in Semiarid Regions http://dx.doi.org/10.5772/101990 73

Sorghum (Sorghum bicolor L. Moench) is an appropriate grass for silage with agronomic and nutritional characteristics, because it is tolerant to drought and responds even in soils with limited nutrients [30] and its phenotypic characteristics facilitate planting, management, harvesting, and storage. The other significant characteristic of sorghum is that it will regrowth

The sorghum is a resistant to hydric deficit in semiarid. Their resistance is associated with the physiology characteristics and efficiency of rain. Researchers evaluated the efficiency of rain in sorghum genotypes in semiarid and found positive results, values between 944.37 and 126.25

In addition to their agronomic traits, sorghum has desirable characteristics for fermentation, such as a suitable dry matter content, high carbohydrate concentration, and low of buffering

Sorghum is a crop that has desirable characteristics for the production of silage; however, as the WSC concentration is higher in the stem, forage sorghum and saccharine sorghum usually have high concentration of carbohydrates, which can facilitate the multiplication of yeasts, molds, and enteric bacteria. The presence these microorganisms cause losses in silage process

In general, the fermentation losses imply in the reduction of the availability of the ensiled forage, since there is no way to recover the DM losses in the form of gases and effluent.

The exposure of silage to air, converting the anaerobic environment (responsible for the conservation of forage) to aerobic, can cause changes in its chemical composition, altering its nutritional value, because the population of microorganisms that were dormant (bacteria,

There is reduction in soluble components of silage, which are used as substrates for these microorganisms [30] and may even be a degraded part of the fibrous portion of food by fungal

Evaluation of the aerobic stability of sorghum silages [26] found the aerobic deterioration losses of 85.6 kg/t DM in silages upon exposure to air during 48 hours. As the air to silage exposure is unavoidable during discharge, many research studies aim to reduce the aerobic

The adding urea to acidic silage can neutralize part of acidity in the chemical reaction by partial neutralization, where, in an acid environment, an agent that has alkalizing action forms

Chemical additives such as urea can also benefit from the silage sorghum (Table 4). Although sorghum silage with urea present pH values and higher N ammonia, it does not mean that the

salts of organic acids [37] and subsequently providing the nitrogen applied [24].

yeasts, and then mold action) and with oxygen began intense metabolic activity [35].

kg DM/ha/mm that indicated high efficiency in covert water of rain in production [32].

and cactus pear.

after each harvesting [31].

substance content [33, 34].

of sorghum.

microbiota [28].

deterioration with the use of additives [36].

4.1. Sorghum

The energy and dry matter disappearance is an indicative of losses in the ensiling process. The residual respiration during filling the silo and immediately after sealing, types of fermentation, effluent production, undesirable fermentation during the storage, and aerobic deterioration are the main causes of energy and dry matter losses [21].

The losses related to respiration usually occur early. The respiration in silo initially occurs due to the presence of oxygen in the ensiled materials, thus the cellular respiration use the air oxygen and substrates producing CO2, heat, and H2O. Some factors can affect the respiration rate in the silo, such as temperature, which increase the initial rate of reaction and destruction of enzymes, usually by denaturation; oxygen concentration, the high amount of oxygen in the silo promotes an increase in the respiration rate and higher the temperature, and consume more energy; WSC content: the amount of soluble substrates in ensiled materials can influence the respiration, since they are consumed during respiration.

Silage fermentation usually causes DM losses due to the activity of microbial and enzymes. The losses related to the fermentation represent the highest percentage of losses in the silage process. These losses can be resulting from the production of water, gas, heat, and effluents during the fermentation process [22].

The effluent losses are associated with the DM content of plant, the activity of the water metabolism and the physical procedure of cutting and application of additives in ensiled forage [23] and DM losses can be highly variable [16]. After evaluating the sorghum silages in Brazilian semiarid we observed a variation of 10–24% DM losses.

In ensiling, besides DM losses, nutritional losses should also be taken into account. Sugarcane and sorghum silages can show high nutritional losses because of a high content of WSC, which may result in increase in alcoholic fermentation. Many studies indicate that the application of additives in the ensiled material considerably reduced these losses of substrates [24–26].

Other fermentation can also occur and reduce the nutritive value of silage, as proteolysis. The proteolysis is associated with DM, protein, WSC content, pH, and ensiling time [27]. It is an undesired reaction because the resulting products of the process (ammonia and amines, principally) indicate high nutritional losses.

In discharge of silo to offer silage to animals aerobic deterioration can also occur, which is one of the main problems after exposure to air [28]. This process occurs due the penetration of air in ensiled materials, which is favorable for the grown of aerobic microorganisms, acid tolerant, and the oxide products resulting in silage fermentative process [29]. The air exposure of silage can chance its chemical compositions and alter the nutritional value.
