**6. Final considerations**

fibrous portion of the ensiled forage. Two main processes occurring in ammoniated forage

The ureolysis process is an enzymatic reaction that release ammonia through hydrolysis of urea. The ureolytic bacteria produces urease [an enzyme catalyst present in plants], that acts in the presence of moisture hydrolyzing the urea and producing two ammonia molecules

From the urea hydrolysis occur chemical reaction ammoniolysis between the ammonia and the ester bonds existing between chains of hemicelluloses and between groups of carbohy‐ drates or carbohydrate molecules and lignin, resulting in formation of an amide [52]. The ammoniolysis cause lysis on bonds between the structural carbohydrates releasing and

In addition, there is another important factor to consider, ammonia has a high affinity for water resulting in the formation of weak base, ammonium hydroxide [NH4OH]. The high affinity of ammonia to water promotes expansion and rupture of the cell wall components of tissues of forage treated with urea. Through specific studies using electron microscopy, change of cell

Another chemical additive, propionic acid is used as antifungal agent able of preserve forage for much time. It inhibits undesirable microorganisms and improves the aerobic stability of

In an experiment test, Chen et al. [54] evaluated the effects and propionic acid applied on the fermentation quality and aerobic stability of total mixed ration silage (TMR) prepared with whole‐plant corn in Tibet. They applied 0.4% propionic acid on a fresh matter basis of TMR, and found higher WSC concentration (88.92 g/kg DM) and decrease in butyric acid content (0.04 g/kg DM) in TMR after 45 days of ensiling, comparative to no additive TMR (WSC = 39.99 g/kg DM; butyric acid content = 0.19 g/kg DM). In aerobic stability assay, TMR silage with propionic acid showed low pH, higher WSC concentration and lower ammonia content than

[which acts directly on the cell wall of forage] and one carbon dioxide [48, 51].

increasing the contact surface to the rumen microorganisms [53].

no additive TMR silage after 12 days of air exposure (**Table 6**).

**Control TMR silage TMR silage with 0.4% propionic acid**

pH 3.90 4.28 5.1 7.07 3.89 3.88 3.87 3.75 LA 86.53 66.95 38.63 15.49 65.44 83.34 83.42 67.09 WSC 39.99 29.16 34.64 29.56 88.92 78.23 72.23 54.23

NH3‐N 52.83 51.87 55.38 65.59 42.48 41.94 51.72 57.36

**Table 6.** Chemical characteristics of total mixture ration silages (TMR) at opening silo and after exposure to air.

**0 6 9 12 0 6 9 12**

mass with urea: ureolysis and ammoniolysis.

114 Advances in Silage Production and Utilization

wall can be seen [49].

*Source:* Adapted from Chen et al. [54].

silages [54].

The ensiling process is complex and yields a variety of end‐products of fermentation. These products can influence directly and indirectly the intake and digestibility of silage. Some control mechanisms of this fermentation can be of use for improvement on intake and digestibility.

Biological or chemical nature, additives may contribute to the increased intake of silage, as well as improve digestibility. To choose the ideal additive, it is necessary to understand the factors that limit the intake and digestibility of food.

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The exposure of silage to air is an inevitable phase and which may compromise the nutritional value of the silage when realized incorrectly. Appropriate management techniques can influence the result.
