**3. Factors that interfere on the silage intake**

The dry matter intake (DMI) is determinant to ingress of nutrients to cater to the requirements for animal maintenance and production, principally the intake of protein and energy [10]. The DMI is the factor that affects the animal productive performance, since 60–90% variation in animal performance is associated with the metabolizable energy intake and only 10–40% with the diet digestibility [11].

with the decrease in silage intake. Then it is possible that cactus palm silage may show a high

Chemical composition of forage pass by changes that alter the forage structure ensiling (**Table 2**). When ensiling, maize showed decrease in WSC (‐59.5 g/kg DM), Neutral detergent fiber (NDF) (‐25 g/kg DM), hemicellulose (‐25 g/kg DM) and cellulose contents (‐11g/kg DM),

**Crop Chemical composition Author**

**ADF (g/kg DM)**

Fresh maize 297.0 – 88.0 555.0 325.0 57.0 230.0 268.0 – Filya and Sucu [18] Maize silage 297.0 – 28.5 530.0 325.0 68.0 205.0 257.0 – Filya and Sucu [18] Fresh sorghum 361.0 108.0 67.0 608.0 359.0 65.0 – – 46.0 Amer et al. [57] Sorghum silage 352.0 116.0 18.0 609.0 361.0 43.0 – – 50.0 Amer et al. [57]

Fresh calliandra 450.5 212.1 – 551.8 488.8 215.7 63.0 299.8 – Ridwan et al. [15] Calliandra silage 465.4 202.2 17.9 538.4 448.8 134.1 89.6 307.0 – Ridwan et al. [15] Fresh Piatã grass 184.0 139.0 – 673.0 372.0 43.0 – – – Costa et al. [59] Piatã grass silage 265.5 97.8 – 632.5 405.8 43.0 – – – Costa et al. [59]

Some forage after ensiling, as Pearl Millet and Calliandra, show increase in the DM content and decrease in CP concentration and fibrous fractions of forage (NDF, NDA, ADL, hemicel‐ lulose and cellulose). The reduction in fibrous fraction is positive to silage degradability,

Others forages, such as sorghum, may show higher ash content after ensiling. This can occurs due the biochemistry reactions of organic acids and salt formation. The exposure of the silage to air, making the anaerobic environment to aerobic, is one of the factors that influence the

because it expands the activity area of rumen microorganisms and resealing energy.

**ADL (g/kg DM)**

230.8 116.8 – 595.0 321.4 – 273.6 279.8 – Guimarães Jr. [58]

241.9 112.5 – 486.8 288.8 – 198.1 256.2 – Guimarães Jr. [58]

312.5 45.2 – 746.2 510.1 382.0 236.2 73.5 Ridwan et al. [15]

311.9 56.0 – 665.8 492.1 343.6 173.7 87.9 Ridwan et al. [15]

**HEM (g/kg DM)**

**CELL (g/kg DM)**

**ASH (g/kg DM)**

Intake and Digestibility of Silages http://dx.doi.org/10.5772/65280 105

**NDF (g/kg DM)**

and increase on acid detergent lignin (+11 g/kg DM) [18].

**WSC (g/kg DM)**

**Table 2.** Chemical composition of pre‐ensiling of forage and silage.

animal intake index.

Fresh pearl millet

Pearl millet silage

Fresh *P. Purpureum*

*P. Purpureum* Silage

**DM CP**

**(g/kg DM)** 

The silage fermentative profile can influence the animal intake. In **Table 1**, the fermentative profile of some silages used in animal feed is described. The corn silage (*Zea mays* L.) shows a good fermentation process and result in adequate lactic acid production (38.6 g/kg DM), low acetic, propionic and butyric acid concentrations [12], which implies adequate dry matter intake.

The sorghum silage (*Sorghum bicolor* L. Moench) has similar fermentative characteristics of corn silage, but in some cases, the higher WSC content of forage can cause acid silage and increase the ethanol produce due to yeast activity [13]. The lactic acid production in sorghum ensilage is quick and pH may decrease below than desirable pH. Sorghum silage can show average values lactic acid of 61.5 g/kg DM and 18 g/kg ethanol concentration [13]. Ethanol may result in decrease in DMI, so excess ethanol is a negative point in these silages.

Another important forage to semiarid regions is the pear millet (*Pennisetum glaucum* LR). The fermentative profile of pear millet silage has high volatile fatty acids (VFA) products, with lactic acid 63 g/kg DM and higher propionic acid content (2.8 g/kg DM) [14] than corn and sorghum silages.

The forage species is an important factor for determining the fermentative profile and intake silage. Silages legumes, such calliandra (*Calliandra calothyrsus*), for example, has higher ammonia content (43.5 mM/g DM) [15] compared to corn silage. This large ammonia amount can influence the intake and digestibility of silages.

Alfalfa silage (*Medicago sativa*) have large amount of organic acid. Research evaluation of replacing effects of alfalfa silage for corn silage, Hassanat et al. [12] found different concen‐ trations of organic acids into silages. The lactic acid content of alfalfa silage (74.2 g/kg DM) is higher than corn silage. However, other compounds such as acetic acid and ammonia can decrease intake silage. The high values found (acetic acid 26.1 g/kg DM and ammonia 27.7 mM/g DM) may have negatively influenced the silage intake by cows. The silage intake increased according to elevated levels of corn silage in the diet. Probably, the differences of the fermentative profile of silages alter the intake by the animal.

Grasses ensiling result generally in higher pH and lower values of lactic acid. Resistance to change in pH or buffer capacity is one of the main obstacles to the quality of silage. The rapid lowering of the pH is effective in reducing the activity of deleterious microorganisms to nutrient forage ensiled. Although the buffering substance content may hamper acidification of the silo environment, Rong et al. [16] observed pH values of 4.1 in Napiergrass (*Pennisetum purpureum* Schum) silage; still, high butyric (12.1 g/kg DM) and acetic acid concentrations (12.7 g/kg DM) and ammonia content (100 g/kg NT). Butyric acid can negatively influence the silage intake in ruminant animals [2].

In semiarid regions, the use of cactaceous in animal feeding is unexceptional. Nogueira [17] tested the cactus palm (*Opuntia ficus* indica) ensiling and found large amount of lactic acid (80.2 g/kg DM) and a high propionic acid content (8.1 g/kg DM). These acids have no relation with the decrease in silage intake. Then it is possible that cactus palm silage may show a high animal intake index.

animal performance is associated with the metabolizable energy intake and only 10–40% with

The silage fermentative profile can influence the animal intake. In **Table 1**, the fermentative profile of some silages used in animal feed is described. The corn silage (*Zea mays* L.) shows a good fermentation process and result in adequate lactic acid production (38.6 g/kg DM), low acetic, propionic and butyric acid concentrations [12], which implies adequate dry matter

The sorghum silage (*Sorghum bicolor* L. Moench) has similar fermentative characteristics of corn silage, but in some cases, the higher WSC content of forage can cause acid silage and increase the ethanol produce due to yeast activity [13]. The lactic acid production in sorghum ensilage is quick and pH may decrease below than desirable pH. Sorghum silage can show average values lactic acid of 61.5 g/kg DM and 18 g/kg ethanol concentration [13]. Ethanol may result

Another important forage to semiarid regions is the pear millet (*Pennisetum glaucum* LR). The fermentative profile of pear millet silage has high volatile fatty acids (VFA) products, with lactic acid 63 g/kg DM and higher propionic acid content (2.8 g/kg DM) [14] than corn and

The forage species is an important factor for determining the fermentative profile and intake silage. Silages legumes, such calliandra (*Calliandra calothyrsus*), for example, has higher ammonia content (43.5 mM/g DM) [15] compared to corn silage. This large ammonia amount

Alfalfa silage (*Medicago sativa*) have large amount of organic acid. Research evaluation of replacing effects of alfalfa silage for corn silage, Hassanat et al. [12] found different concen‐ trations of organic acids into silages. The lactic acid content of alfalfa silage (74.2 g/kg DM) is higher than corn silage. However, other compounds such as acetic acid and ammonia can decrease intake silage. The high values found (acetic acid 26.1 g/kg DM and ammonia 27.7 mM/g DM) may have negatively influenced the silage intake by cows. The silage intake increased according to elevated levels of corn silage in the diet. Probably, the differences of the

Grasses ensiling result generally in higher pH and lower values of lactic acid. Resistance to change in pH or buffer capacity is one of the main obstacles to the quality of silage. The rapid lowering of the pH is effective in reducing the activity of deleterious microorganisms to nutrient forage ensiled. Although the buffering substance content may hamper acidification of the silo environment, Rong et al. [16] observed pH values of 4.1 in Napiergrass (*Pennisetum purpureum* Schum) silage; still, high butyric (12.1 g/kg DM) and acetic acid concentrations (12.7 g/kg DM) and ammonia content (100 g/kg NT). Butyric acid can negatively influence the silage

In semiarid regions, the use of cactaceous in animal feeding is unexceptional. Nogueira [17] tested the cactus palm (*Opuntia ficus* indica) ensiling and found large amount of lactic acid (80.2 g/kg DM) and a high propionic acid content (8.1 g/kg DM). These acids have no relation

in decrease in DMI, so excess ethanol is a negative point in these silages.

can influence the intake and digestibility of silages.

fermentative profile of silages alter the intake by the animal.

intake in ruminant animals [2].

the diet digestibility [11].

104 Advances in Silage Production and Utilization

intake.

sorghum silages.

Chemical composition of forage pass by changes that alter the forage structure ensiling (**Table 2**). When ensiling, maize showed decrease in WSC (‐59.5 g/kg DM), Neutral detergent fiber (NDF) (‐25 g/kg DM), hemicellulose (‐25 g/kg DM) and cellulose contents (‐11g/kg DM), and increase on acid detergent lignin (+11 g/kg DM) [18].


**Table 2.** Chemical composition of pre‐ensiling of forage and silage.

Some forage after ensiling, as Pearl Millet and Calliandra, show increase in the DM content and decrease in CP concentration and fibrous fractions of forage (NDF, NDA, ADL, hemicel‐ lulose and cellulose). The reduction in fibrous fraction is positive to silage degradability, because it expands the activity area of rumen microorganisms and resealing energy.

Others forages, such as sorghum, may show higher ash content after ensiling. This can occurs due the biochemistry reactions of organic acids and salt formation. The exposure of the silage to air, making the anaerobic environment to aerobic, is one of the factors that influence the nutritional value of silages. In the presence of air, deleterious and opportunistic aerobic microorganisms can develop rapidly and degrade nutrients from silages.

intake problem [21]. The end‐products of fermentation in silage can affect the animal intake

The regulation of intake in ruminants can occur through of humoral factors because the volatile fatty acids (VFA) have the ability to limit the intake. The intake varies with the energy requirements of the animal. The physiological mechanism can be observed when provided with high concentrate diets, as animals in confinement. As silage has a considerable content of organic acids due the fermentative process, the intake of silage tends to be lower than the original forage. Some silage fermentation products can reduce the intake of silage, such as

Animals with diet rich in forage prevails the intake limited by the physical capacity rumen. The NDF is the main fraction of diet that provides this effect because it is slow and incomplete digestion in gastrointestinal [11]. In this situation, repletion has a significant effect on animal capacity in DM intake. The physical distension of the reticulum‐rumen is the main factor

Fiber fraction is an important parameter to be considered for the animal intake, because it is negatively correlated with intake and digestibility [7]. Even with the lower fiber content when compared to hay, silage tends to be less intake by the animals. In the experiment evaluating the effects of fermentation on the intake and digestibility of silage [24], the authors found an average of 16% lower intake of silage compared to the intake of hay. They noted that this

The major source of ingredients in dairy cow diets is the forage. Despite their important (economically and nutritionally), the forage has been a study object for a long time [12].

**IVD (%DM) TIVD (%DM) AD (%DM)**

Corn silage 22.80 – – 71.30 Cow Hassanat et al. [12] Alfalfa silage 21.70 – – 69.70 Cow Hassanat et al. [12] Sugarcane *in natura* – 63.93 66.50 – – Balieiro Neto et al. [8] Sugarcane silage – 59.72 62.11 – – Balieiro Neto et al. [8] Sorghum silage (SS) 5.91 – – 48.32 Sheep Simon et al. [35] SS + 15% concentrate 7.09 – – 61.96 Sheep Simon et al. [35] SS + 15% concentrate 7.81 – – 68.12 Sheep Simon et al. [35] SS + 15% concentrate 7.98 – – 69.77 Sheep Simon et al. [35]

**Digestibility Animal**

**species**

**Author**

Intake and Digestibility of Silages http://dx.doi.org/10.5772/65280 107

limiting the intake of fodder and many diets rich in fiber [14].

reduction in intake was due to the presence of fermentation end‐products.

IVD = *in vitro* digestibility; TIVD = true *in vitro* digestibility; AD = apparent digestibility.

through palatability [22]. In addition, the palatability depends on the animal species.

acetic acid [23].

**Crop Intake dry**

**Table 4.** Intake and digestibility of silage index.

**matter (kg/d)**

Sugarcane and corn are forage susceptible to aerobic stability problems because the high lactic acid concentration and residual WSC promote an ideal environment for the development of deleterious microorganisms, such yeasts. In **Table 3**, it is observed that after exposure to air over time (8 and 9 days), there was a reduction in the WSC content of corn silage and an increased DM content [8]. The sugarcane silages showed an increase in the NDF and CP contents and reduced lignin (ADL) and non‐fibrous carbohydrate (NFC) contents [19]. These changes in the chemical composition of silages can interfere on intake and digestibility of silages.


**Table 3.** Changes in the chemical composition of fresh forage, silage at silo opening and silage exposure to air.

In ruminant animals, the intake is regulated by psychogenic, physiological or physical mechanisms [11]. The psychogenic mechanism is related to aspects of smell and palatability of the food [20].

Palatability is the property of a food that affects its taste or smell as perceived by animals with particular experiences under specified conditions. The palatability may be a basis to the silage intake problem [21]. The end‐products of fermentation in silage can affect the animal intake through palatability [22]. In addition, the palatability depends on the animal species.

The regulation of intake in ruminants can occur through of humoral factors because the volatile fatty acids (VFA) have the ability to limit the intake. The intake varies with the energy requirements of the animal. The physiological mechanism can be observed when provided with high concentrate diets, as animals in confinement. As silage has a considerable content of organic acids due the fermentative process, the intake of silage tends to be lower than the original forage. Some silage fermentation products can reduce the intake of silage, such as acetic acid [23].

Animals with diet rich in forage prevails the intake limited by the physical capacity rumen. The NDF is the main fraction of diet that provides this effect because it is slow and incomplete digestion in gastrointestinal [11]. In this situation, repletion has a significant effect on animal capacity in DM intake. The physical distension of the reticulum‐rumen is the main factor limiting the intake of fodder and many diets rich in fiber [14].

Fiber fraction is an important parameter to be considered for the animal intake, because it is negatively correlated with intake and digestibility [7]. Even with the lower fiber content when compared to hay, silage tends to be less intake by the animals. In the experiment evaluating the effects of fermentation on the intake and digestibility of silage [24], the authors found an average of 16% lower intake of silage compared to the intake of hay. They noted that this reduction in intake was due to the presence of fermentation end‐products.

The major source of ingredients in dairy cow diets is the forage. Despite their important (economically and nutritionally), the forage has been a study object for a long time [12].


IVD = *in vitro* digestibility; TIVD = true *in vitro* digestibility; AD = apparent digestibility.

**Table 4.** Intake and digestibility of silage index.

nutritional value of silages. In the presence of air, deleterious and opportunistic aerobic

Sugarcane and corn are forage susceptible to aerobic stability problems because the high lactic acid concentration and residual WSC promote an ideal environment for the development of deleterious microorganisms, such yeasts. In **Table 3**, it is observed that after exposure to air over time (8 and 9 days), there was a reduction in the WSC content of corn silage and an increased DM content [8]. The sugarcane silages showed an increase in the NDF and CP contents and reduced lignin (ADL) and non‐fibrous carbohydrate (NFC) contents [19]. These changes in the chemical composition of silages can interfere on intake and digestibility of

> **ADF (g/kg DM)**

340.5 38.9 659.7 493.3 82.3 245.2 – –

359.2 37.8 709.7 440.4 69.2 195.8 – –

299.7 42.7 704.7 414.6 59.4 196.0 – –

Sugarcane 269.1 30.0 554.8 439.5 72.5 375.8 – – Sugarcane silage 238.2 31.9 633.3 479.2 83.7 282.0 – –

Maize 339 71 409 198 – – – 35 Maize silage 317 78 384 206 – – 18 37 Maize silage (d0) 360 75 354 203 – – 17 35 Maize silage (d2) 366 73 370 209 – – 18 37 Maize silage (d4) 371 76 358 217 – – 15 35 Maize silage (d6) 389 75 356 208 – – 9 35 Maize silage (d8) 395 76 362 206 – – 11 35

**Table 3.** Changes in the chemical composition of fresh forage, silage at silo opening and silage exposure to air.

In ruminant animals, the intake is regulated by psychogenic, physiological or physical mechanisms [11]. The psychogenic mechanism is related to aspects of smell and palatability

Palatability is the property of a food that affects its taste or smell as perceived by animals with particular experiences under specified conditions. The palatability may be a basis to the silage

**ADL (g/kg DM)**  **NFC (g/kg DM)**  **WSC (g/kg DM)**  **ASH (g/kg DM)** 

microorganisms can develop rapidly and degrade nutrients from silages.

**NDF (g/kg DM)** 

silages.

Sugarcane silage

Sugarcane silage

Sugarcane silage

of the food [20].

(d3)

(d6)

(d9)

**Crop Chemical composition DM (g/kg DM)** 

106 Advances in Silage Production and Utilization

**CP (g/kg DM)** 

*Source:* Adapted from Balieiro Neto et al. [8] and Gerlach et al. [19].

Evaluating the effect of replacing alfalfa silage to corn silage on diet intake of dairy cows, among other parameters, Hassanat et al. [12] found values of 21.7 kg/day DMI alfalfa silage and 22.8 kg/day DMI corn silage (**Table 4**). The difference on intake silage in these silages may occur due chemical composition and fermentative profile. As mentioned before, butyric and acetic acid are associated with decreased intake silages. These acids were found in greater quantity in alfalfa silage than in corn silage.

In a study on the effect of aerobic deterioration of silage on goat intake, the authors found intense degradation of lactic (by yeasts) and acetic acids, decrease in WSC after air exposure. After eight days, it was more than half with reductions ranging between 29 and 79% in comparison to fresh silages. Some end‐products of fermentation (ethyl lactate, ethanol) were negatively related to silage intake. However, correlation coefficients were weak. Concentra‐ tions of acetic acid and ethanol were negatively correlated with DMI, but the authors justified that lower DMI is due to the greater concentration of acetic acid in fresh silages which compensate for improved aerobic stability and smaller decline in DMI is a consequence of

Intake and Digestibility of Silages http://dx.doi.org/10.5772/65280 109

The lactic acid is an organic acid produced by conversion of soluble carbohydrates by lactic acid bacteria. The lactic acid content should be at least 65–70% of the total silage acids in good

The lactic acid concentration in silages may to decrease the efficiency of microbial protein

Extremely wet silages or slow silo filling can result in silages with high concentrations of acetic acid (>3–4% of DM). Acetic acid concentrations are also related principally to long‐acting of

The acetic acid content negatively relates to the intake of silage [28], therefore low levels of acetic acid are desirable in silages [29]. Though it may present a negative aspect to intake, silage inoculants specific with the largest production of acetic acid did not show a reduction in animal

In assay sheep fed with silage, the authors [21] found decrease in the intake of silage when adding acetic acid. The reduction in intake is justified due to the taste and odor of silage. In

Concentrations of butyric acid are negatively correlated with digestibility [24]. A high concentration of butyric acid (>0.5% of DM) indicates that the silage has a poor fermentation, clostridia fermentation. Silages high in butyric acid have a low nutritive value and many of the soluble nutrients have been degraded. They may contain compounds such as amines that

The butyric acid content reflects clostridia activity on ensiled mass with a deleterious effect on

have sometimes shown adversely affect animal performance, also the intake [26].

synthesis in the rumen whenever the values are high [27].

enterobacteria and heterofermentative bacteria [26].

quality and reduction of silage palatability [29].

other studies, DMI was negatively correlated with acetic acid [19].

aerobic deterioration [19].

*3.1.1. Lactic acid*

silage [26].

*3.1.2. Acetic acid*

intake [26].

*3.1.3. Butyric acid*

### **3.1. End‐products of fermentation**

The ensilage is a complex process and it yields a variety of compounds and forage quality is a term used to refer to the nutritional value of plant in interaction with the animal intake and performance potential. About silage, the animal response is dependent on its fermentative profile that affects the food structure, nutrient concentration and intake [3].

The quality of the silage is influenced by factors such as plant species, indigenous microbiota, crop management, cutting and ensilage procedure, as well as environmental factors and storage. The variation of silage quality can influence the intake by animals. The composition and concentration of fermentation end‐products of the silage are variable, most commonly found fermentation produces lactic acid, however, other types of fermentations occur and may decline the nutritional quality of the silage [4]. The fermentation quality should be included in assessment of the DMI potential of grass silages [24].

Although intensively discussed, there is no agreement on the indices of fermentation quality when evaluating the dry matter intake of the silage [5, 24], however, some factors may be identified for reducing the intake of silage.

Researchers evaluated the production of fermentative compounds in silages and they found 13 esters, 5 aldehydes, 3 alcohols and 1 sulfide. They observed that the increase in ammonia, acetate and propionate levels, as well as decrease in the WSC content, decrease the intake [22].

Esters are volatile compounds that may take effect on silage flavor reducing the DMI, princi‐ pally acetate [19]. Other compounds also may influence the DMI, as propionic acid and biogenic amine. According to some studies it is improbable that low propionic acid concen‐ tration directly influence the DMI, while the biogenic amine is naturally present in silages and reduce the intake from palatability or by influencing the nitrogen metabolism [5].

An indicator that can be related to the DMI is pH. Researchers evaluating changes in the fermentation of corn silage exposed to air [16] found a positive correlation between pH and DMI, if pH is relatively high, and a greater intake of silage. This is justified because of the absence of excessive organic acids or ammonia‐N fermentation [5, 19].

The fermentation process of the silage not just can generate products that inhibit the animal intake; the reactions resulting from the silo opening procedure can also promote reduction of silage intake. The aerobic deterioration is a significant problem that affects the yield and quality of silage [25]. It is caused by the activity of bacteria, yeasts and molds that can compromise the final nutritional value of the silage, changing the volatile and depressed intake [19].

In a study on the effect of aerobic deterioration of silage on goat intake, the authors found intense degradation of lactic (by yeasts) and acetic acids, decrease in WSC after air exposure. After eight days, it was more than half with reductions ranging between 29 and 79% in comparison to fresh silages. Some end‐products of fermentation (ethyl lactate, ethanol) were negatively related to silage intake. However, correlation coefficients were weak. Concentra‐ tions of acetic acid and ethanol were negatively correlated with DMI, but the authors justified that lower DMI is due to the greater concentration of acetic acid in fresh silages which compensate for improved aerobic stability and smaller decline in DMI is a consequence of aerobic deterioration [19].

## *3.1.1. Lactic acid*

Evaluating the effect of replacing alfalfa silage to corn silage on diet intake of dairy cows, among other parameters, Hassanat et al. [12] found values of 21.7 kg/day DMI alfalfa silage and 22.8 kg/day DMI corn silage (**Table 4**). The difference on intake silage in these silages may occur due chemical composition and fermentative profile. As mentioned before, butyric and acetic acid are associated with decreased intake silages. These acids were found in greater

The ensilage is a complex process and it yields a variety of compounds and forage quality is a term used to refer to the nutritional value of plant in interaction with the animal intake and performance potential. About silage, the animal response is dependent on its fermentative

The quality of the silage is influenced by factors such as plant species, indigenous microbiota, crop management, cutting and ensilage procedure, as well as environmental factors and storage. The variation of silage quality can influence the intake by animals. The composition and concentration of fermentation end‐products of the silage are variable, most commonly found fermentation produces lactic acid, however, other types of fermentations occur and may decline the nutritional quality of the silage [4]. The fermentation quality should be included

Although intensively discussed, there is no agreement on the indices of fermentation quality when evaluating the dry matter intake of the silage [5, 24], however, some factors may be

Researchers evaluated the production of fermentative compounds in silages and they found 13 esters, 5 aldehydes, 3 alcohols and 1 sulfide. They observed that the increase in ammonia, acetate and propionate levels, as well as decrease in the WSC content, decrease the intake [22].

Esters are volatile compounds that may take effect on silage flavor reducing the DMI, princi‐ pally acetate [19]. Other compounds also may influence the DMI, as propionic acid and biogenic amine. According to some studies it is improbable that low propionic acid concen‐ tration directly influence the DMI, while the biogenic amine is naturally present in silages and

An indicator that can be related to the DMI is pH. Researchers evaluating changes in the fermentation of corn silage exposed to air [16] found a positive correlation between pH and DMI, if pH is relatively high, and a greater intake of silage. This is justified because of the

The fermentation process of the silage not just can generate products that inhibit the animal intake; the reactions resulting from the silo opening procedure can also promote reduction of silage intake. The aerobic deterioration is a significant problem that affects the yield and quality of silage [25]. It is caused by the activity of bacteria, yeasts and molds that can compromise the

final nutritional value of the silage, changing the volatile and depressed intake [19].

reduce the intake from palatability or by influencing the nitrogen metabolism [5].

absence of excessive organic acids or ammonia‐N fermentation [5, 19].

profile that affects the food structure, nutrient concentration and intake [3].

in assessment of the DMI potential of grass silages [24].

identified for reducing the intake of silage.

quantity in alfalfa silage than in corn silage.

**3.1. End‐products of fermentation**

108 Advances in Silage Production and Utilization

The lactic acid is an organic acid produced by conversion of soluble carbohydrates by lactic acid bacteria. The lactic acid content should be at least 65–70% of the total silage acids in good silage [26].

The lactic acid concentration in silages may to decrease the efficiency of microbial protein synthesis in the rumen whenever the values are high [27].

#### *3.1.2. Acetic acid*

Extremely wet silages or slow silo filling can result in silages with high concentrations of acetic acid (>3–4% of DM). Acetic acid concentrations are also related principally to long‐acting of enterobacteria and heterofermentative bacteria [26].

The acetic acid content negatively relates to the intake of silage [28], therefore low levels of acetic acid are desirable in silages [29]. Though it may present a negative aspect to intake, silage inoculants specific with the largest production of acetic acid did not show a reduction in animal intake [26].

In assay sheep fed with silage, the authors [21] found decrease in the intake of silage when adding acetic acid. The reduction in intake is justified due to the taste and odor of silage. In other studies, DMI was negatively correlated with acetic acid [19].

### *3.1.3. Butyric acid*

Concentrations of butyric acid are negatively correlated with digestibility [24]. A high concentration of butyric acid (>0.5% of DM) indicates that the silage has a poor fermentation, clostridia fermentation. Silages high in butyric acid have a low nutritive value and many of the soluble nutrients have been degraded. They may contain compounds such as amines that have sometimes shown adversely affect animal performance, also the intake [26].

The butyric acid content reflects clostridia activity on ensiled mass with a deleterious effect on quality and reduction of silage palatability [29].

#### *3.1.4. Ammonia*

The ammonia‐N is often associated with the decrease in the intake of silage because of their presence in poorly fermented silage or clostridia. Some other products resulting of degradation of amino acids also can decrease the intake of silage [21].

The yield of fermentation end‐products in silage is variable, depending primarily on the amount of substrates and microbial flora. Some silage may contain up to 200 g/kg DM of fermentation end‐products, especially lactic acid and VFA, which provide low energy for the

Intake and Digestibility of Silages http://dx.doi.org/10.5772/65280 111

Other factors such as exposure to air and use of additives can influence silage digestibility. The fermentation type interferes in the result of silage intake and digestibility. Corn and alfalfa silages have different digestibilities (**Table 4**). Compared to fresh forage, digestibility of silages

The use of additives as concentrate ration can increase intake and digestibility of silages. The total mixture ration is an efficient technique and may increase intake and digestibility of silages,

The fresh forage has approximately 75–90% of the total nitrogen present in the protein form [29], the rest called non‐protein nitrogen comprises free amino acids and amides, and ammonia with concentration less than 1% of total nitrogen. During the fermentative process of silage, part of nitrogen fraction is degraded to soluble fractions as peptides, amino acids and ammo‐ nia, which are rapidly degraded in the rumen with low microbial synthesis efficiency and

According to the research of Mckersie, in 1985 [29], compounds resulting from proteolysis and degradation of amino acids formed during fermentation of silage can inhibit the intake and have low utilization efficiency of the microorganisms present in the rumen [29]. The concen‐ tration of ammonia in good silages should be low, not to influence the silage intake negatively

During the ensiling process the breakdown of hemicelluloses occurs to provide additional substrate for the fermentation, because concentrations of NDF in the silages are lower than the original herbage. The degradation of hemicellulose also can occur through hydrolysis by

Compared with the herbage, concentrations of NDF can be altered by breaking the nitrogen bound to NDF, but an increase in the concentrations of NDF and ADL in silage may occur due to DM losses or effluent losses of soluble nutrients [24]. Concentration of ADL increases also due to synthesis of Maillard polymers [7], which may present positive correlation with ADIN. The changes in the fiber fractions attributable to the fermentative process of silage could

Researchers evaluating different proportions of sorghum silage in diet of beef cattle compared to Tifton grass pre‐dry, found an increase in dry matter, organic matter and total carbohydrate digestibility on adding a higher proportion of sorghum silage to diet. The authors justified that the increase of digestibility occurs due the lower NDF proportion and greater TDN (total digestible nutrients) which has rapid and complete availability in the gastrointestinal tract [10].

rumen microorganisms [34].

[7].

is lower [8], but this can be modified.

organic acids or action additives [4].

influence digestibility [24].

obtaining considerable increases in apparent digestibility [35].

results in inappropriate protein post‐rumen flow [36].

**4.1. Changes in the fermentation process that affects silage digestibility**

Degradability of silage is positively correlated with WSC and LA [24].

The proteolysis by plant and microbial enzymes may lower the nutritive value of ensiling forage by degrading the forage protein fraction into peptides, amines, free amino acids and ammonia. This permit proteolytic bacteria ferment peptides and amino acids converting them into a diversity of organic acids, CO2, ammonia and amines, products that decrease the voluntary intake of silage [30]. Generally, the ammonia concentration is used as an indicator of protein degradation in silage [5].

Although microorganisms as enterobacteria have low proteolytic activity, it can deaminate and decarboxylate some amino acids contributing to the formation of ammonia and biogenic amines in silage, which have a negative effect on silage palatability and intake in ruminants [31].

Ammonia concentrations are negatively related to the intake of silage. In grass silage, high moisture favors the butyric fermentation and release of ammonia, which negatively affect the intake of silage by animals [1]. According to Huhtanen et al. [5] index, ammonia concentrations greater than 50 g/kg N predict decrease in silage DMI.
