**4. Factors that affect silage digestibility**

Digestion is a process of conversion of food macromolecules into simple compounds that can be absorb into the gastrointestinal tract [10].

Concentration of ammonia‐N in rumen is indispensable for microbial growth since it is associated with the energy source, and it is related to soluble protein of diet and to N retention of the animal. High ammonia concentrations may occur when excess protein in the diet is degraded in the rumen or a low concentration of carbohydrates is degraded in the rumen, which can cause changes in rumen pH changing the microbial activity and its functions in the digestive process [10].

The digestibility of ruminants is associated with the characteristics of food and the animal. The relationship between intake and digestibility, in which the increase in digestibility leads to increased intake, is influenced by forage residence time in the rumen [32].

Some factors, such as the proper processing of forage for silage, contribute to improve the digestibility of the final product. Researchers evaluated the effect of the length of the whole plant corn on intake, digestibility and production of milk [33], they found positive results regarding the effect of whole plant processing for corn silage with increased body weight, increased DM intake, greater starch and fiber digestibility. Still, the estimated average increase in starch digestibility in the ensiled plants was 4.2% above the initial herbage unprocessed digestibility.

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 rumen microorganisms [34].

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

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, obtaining considerable increases in apparent digestibility [35].

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

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

*3.1.4. Ammonia*

110 Advances in Silage Production and Utilization

[31].

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

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

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

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

Digestion is a process of conversion of food macromolecules into simple compounds that can

Concentration of ammonia‐N in rumen is indispensable for microbial growth since it is associated with the energy source, and it is related to soluble protein of diet and to N retention of the animal. High ammonia concentrations may occur when excess protein in the diet is degraded in the rumen or a low concentration of carbohydrates is degraded in the rumen, which can cause changes in rumen pH changing the microbial activity and its functions in the

The digestibility of ruminants is associated with the characteristics of food and the animal. The relationship between intake and digestibility, in which the increase in digestibility leads to

Some factors, such as the proper processing of forage for silage, contribute to improve the digestibility of the final product. Researchers evaluated the effect of the length of the whole plant corn on intake, digestibility and production of milk [33], they found positive results regarding the effect of whole plant processing for corn silage with increased body weight, increased DM intake, greater starch and fiber digestibility. Still, the estimated average increase in starch digestibility in the ensiled plants was 4.2% above the initial herbage unprocessed

increased intake, is influenced by forage residence time in the rumen [32].

of amino acids also can decrease the intake of silage [21].

greater than 50 g/kg N predict decrease in silage DMI.

**4. Factors that affect silage digestibility**

be absorb into the gastrointestinal tract [10].

digestive process [10].

digestibility.

of protein degradation in silage [5].

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

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 [7].

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 organic acids or action additives [4].

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 influence digestibility [24].

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]. The exposure to air of silages affects the silage digestibility. The effects of air on silage can reduce the digestibility (**Table 5**). Sugarcane silage show lower digestibility than fresh sugarcane, and after 3, 6 and 9 days of exposure to air, sugarcane silage has reduced 7.20% of *in vitro* digestibility (IVD) and 2.7% true *in vitro* digestibility (TIVD). This reduction can be avoided or minimized by adequate ensiling management procedures and storage of silage, in addition, to the use of additives.

Recent studies demonstrate that some heterofermentative bacteria [*Lactobacillus buchneri*, for example] produce ferulate‐esterase, enzyme that increases the degradation of the cell wall. This enzyme release considerable soluble carbohydrates for fermentation or for use by rumen

Intake and Digestibility of Silages http://dx.doi.org/10.5772/65280 113

An enzyme‐bacterial inoculant acts in two forms in silage: whereas bacterial inoculants improve fermentation profile and increase lactic acid bacteria population, enzyme inoculants act on the cell wall and the available higher quantity of soluble compounds, with improvement

Researchers study the effect of inoculants on silage, rumen function and digestibility. They found improvements in DM and NDF digestibility after 24 hours of incubation [38]. Others studies also found higher DM and NDF digestibility in inoculated corn silage than untreated

Although there are some positive results, in the experiment realized by Fugita et al. [42], the addition of enzyme‐bacteria inoculants do not significantly influence nutrient intake, per‐

The use of microbial additives in sorghum silage resulted in positive responses to the hemi‐ cellulose content and value on *in vitro* DM digestibility. The lower hemicellulose content of the silage treated compared to control may result from the action of enzymes associated with bacteria, and the greater IVDMD found may reflect the enzymatic hydrolysis effect [45]. However, it has been reported that the effects of LAB inoculants on fiber degradation are not consistent [18] as LAB cannot use fiber as an energy source [46]. The hemicellulose degradation by LAB inoculation is inhibited in lower environmental temperature, requiring optimum

Additives in silage can affect the DM intake and intervene in the nutritive value of silage, as digestibility of nutrients. Chemical additives are substances that act in the control of biochem‐ ical reactions of silage. The inhibitor additives function without distinction in all processes in the silage acting on undesirable microorganisms and fermentations, as the secondary proteol‐ ysis or aerobic growth. Among the main additives chemical inhibitors there are urea [48],

Urea is an additive that contains between 42 and 45% of nitrogen [48], commonly used in fodder ammonization due to ease of application, not a pollutant, but as a source of non‐protein nitrogen, reduce the fibrous portion of forage (NDF), favor the partial solubilization of hemicelluloses, influence the increase in intake and digestibility of silage [49]. According to the classification McDonald et al. [4], urea is also a nutrient additive because it improves the

Researchers showed the increase in the protein content of silage as result of high recovery of nitrogen applied and may reach up 77% recovery [50]. Nitrogen recovery is a positive feature of urea from both the nutritional and economical aspect. Urea also acts beneficially in the

formance and carcass characteristics of feedlot finished crossbred bulls.

bacteria [43].

silage [39].

in silage digestibility [44].

temperature for its activity [47].

**5.2. Use of chemical additive**

propionic and formic acid.

nutritive value of silage.


**Table 5.** Effect of exposure to air on silage digestibility.
