**2. Ruminal enteric fermentation and methanogenesis**

Methanogenesis was once considered a singular type of fermentation. However, in some respects, a very unique biochemistry is involved. The process is carried out by strictly anaerobic bacteria, all of which belong to the phylum *Euryarchaeota* in five orders that include mesophiles and thermophiles: *Methanobacteriales*, *Methanococcales*, *Methanomicrobiales*, *Methanopyrales*, and *Methanosarcinales*. Methanogens can be found in freshwater and marine environments, cold

**121**

*Climate Change Mitigation in Livestock Production: Nonconventional Feedstuffs and Alternative…*

sediments, and hydrothermal vents as free cells living in symbiosis within animals which produce methane as well as in symbiosis with anaerobic methane oxidation-

Ruminal degradation of fiber and starch generates hexoses which later are fermented through the glycolysis pathway. Pyruvate, as a final product of the glycolysis, is converted into volatile fatty acids (VFA), mainly acetic, propionic, and butyric acid, through different metabolic pathways. These VFA are rapidly absorbed by the animal and are used as energy source, while other products such as H2 and CO2 are generated. However, the hydrogen produced in the glycolysis inhibits

when a low H2 pressure is present [7]. Therefore, methane production is essential for obtaining a high-performing rumen ecosystem, because H2 accumulation is avoided, which could then inhibit dehydrogenase activity in later re-oxidation cofactors. An efficient H2 capture in the rumen contributes to increase the rate of fermentation by the lack of its inhibitory effect on the microbial degradation of vegetative material [8, 9]. Hence, thermodynamically methane synthesis is favored. **Figure 1** represents the synergic relationship between *Ruminococcus albus* and

The rumen is an anaerobic bioreactor which contains a great diversity of microorganisms, such as bacteria, fungi, protozoa, and archaea. From all of these, just a few have been cultivable and virtually identified. However, the newer molecular biology techniques have widely contributed to the identification of ruminal microorganisms, as well as the activity from each consortium in the ruminal fermentation. Feedstuffs' degradation in the rumen is effectuated by microorganisms with different goals and at different proportions. In addition, the enzymatic and degradative activity of every consortium may be affected by several factors, such as diet, season, inherent characteristics of the ruminant's breed, geographic zone, feeding strategies, physiological conditions, intake, etc. [11]. Hence, modification in the ruminal fermentation can be achieved by alterations on the previously mentioned variables, showing positive changes in efficiency and productivity of the animal. Therefore, diverse targets have been defined through modification in the ruminal fermentation: (a) to decrease the ruminal methane synthesis through the increase of propionate production; (b) to improve fibers' ruminal digestion; (c) to increase undegradable rumen protein in order to increase the bypass protein to lower tract which later will be absorbed by the animal through the intestine walls; and (d) to reduce rapidly degradable carbohydrates in rumen [12]. According to the latter,

methanogens, as an example of the expressed earlier [10].

diverse options have been studied to cover two or more targets.

Carbohydrate fermentation is the main source of energy for the ruminant. Quantity and quality of rapidly degradable carbohydrates, usually known as

in corn (*Zea mays*) are mostly starch, whereas, in molasses, NFCs are mainly composed by mono- and disaccharides. Depending on the NFC type and the supplied feedstuff, certain pathways for synthesis may be favored. For example, whether increases in the structural carbohydrates are observed, the propionate synthesis pathway is enhanced. This pathway is beneficial to the animal since it reduces methane synthesis [13]. Otherwise, an increase in mono- and disaccharides

nonfibrous carbohydrates (NFCs), depends on the feedstuff. Thus, NFCs contained

ferredoxin oxidoreductase enzyme, which impedes NAD regeneration

*DOI: http://dx.doi.org/10.5772/intechopen.89433*

promoting bacteria [6].

**3. Fermentation modifiers**

**3.1 Nonfibrous carbohydrates**

NADH+H<sup>+</sup>

**Figure 1.**

*Synergic relationship between Ruminococcus albus and methanogens (adapted from [10]).*

*Climate Change Mitigation in Livestock Production: Nonconventional Feedstuffs and Alternative… DOI: http://dx.doi.org/10.5772/intechopen.89433*

sediments, and hydrothermal vents as free cells living in symbiosis within animals which produce methane as well as in symbiosis with anaerobic methane oxidationpromoting bacteria [6].

Ruminal degradation of fiber and starch generates hexoses which later are fermented through the glycolysis pathway. Pyruvate, as a final product of the glycolysis, is converted into volatile fatty acids (VFA), mainly acetic, propionic, and butyric acid, through different metabolic pathways. These VFA are rapidly absorbed by the animal and are used as energy source, while other products such as H2 and CO2 are generated. However, the hydrogen produced in the glycolysis inhibits NADH+H<sup>+</sup> ferredoxin oxidoreductase enzyme, which impedes NAD regeneration when a low H2 pressure is present [7]. Therefore, methane production is essential for obtaining a high-performing rumen ecosystem, because H2 accumulation is avoided, which could then inhibit dehydrogenase activity in later re-oxidation cofactors. An efficient H2 capture in the rumen contributes to increase the rate of fermentation by the lack of its inhibitory effect on the microbial degradation of vegetative material [8, 9]. Hence, thermodynamically methane synthesis is favored. **Figure 1** represents the synergic relationship between *Ruminococcus albus* and methanogens, as an example of the expressed earlier [10].

### **3. Fermentation modifiers**

*Livestock Health and Farming*

In this way, emissions derived from livestock are estimated over 14% of the total anthropogenic greenhouse gases (GHG) emitted to atmosphere, which account approximately 50 gigatons of CO2 equivalents per year (GTons-CO2 equiv./yr) [3]. In addition, livestock is a major non-CO2 GHG producer (CH4 and NO2); these gases possess a higher trapping heat index compared to at least 25 times for CO2 [3]. Climate change effect has risen the average planet temperature approximately 1°C. In fact, polar caps are melting rapidly, which have increased the sea levels as a consequence [3]. If these trends keep on going, the CC effect will reach a nonreturn point, causing irreparably damages to the planet [4]. In addition, the UN encouraged developing countries (mainly Latin American countries) to strengthen their efforts to avoid an increase over 1.5°C in the temperature of the planet. Nevertheless, since CO2 emissions increased substantially in the latest years, a 3°C

Due to the latter, worldwide researchers and governments attempt to mitigate livestock gases production by changing livestock diets and offering alternative feedstuffs as an important strategy to mitigate GHG emissions and CC effect.

Methanogenesis was once considered a singular type of fermentation. However, in some respects, a very unique biochemistry is involved. The process is carried out by strictly anaerobic bacteria, all of which belong to the phylum *Euryarchaeota* in five orders that include mesophiles and thermophiles: *Methanobacteriales*, *Methanococcales*, *Methanomicrobiales*, *Methanopyrales*, and *Methanosarcinales*. Methanogens can be found in freshwater and marine environments, cold

rise of the temperature is expected by the end of the century [5].

**2. Ruminal enteric fermentation and methanogenesis**

**120**

**Figure 1.**

*Synergic relationship between Ruminococcus albus and methanogens (adapted from [10]).*

The rumen is an anaerobic bioreactor which contains a great diversity of microorganisms, such as bacteria, fungi, protozoa, and archaea. From all of these, just a few have been cultivable and virtually identified. However, the newer molecular biology techniques have widely contributed to the identification of ruminal microorganisms, as well as the activity from each consortium in the ruminal fermentation. Feedstuffs' degradation in the rumen is effectuated by microorganisms with different goals and at different proportions. In addition, the enzymatic and degradative activity of every consortium may be affected by several factors, such as diet, season, inherent characteristics of the ruminant's breed, geographic zone, feeding strategies, physiological conditions, intake, etc. [11]. Hence, modification in the ruminal fermentation can be achieved by alterations on the previously mentioned variables, showing positive changes in efficiency and productivity of the animal. Therefore, diverse targets have been defined through modification in the ruminal fermentation: (a) to decrease the ruminal methane synthesis through the increase of propionate production; (b) to improve fibers' ruminal digestion; (c) to increase undegradable rumen protein in order to increase the bypass protein to lower tract which later will be absorbed by the animal through the intestine walls; and (d) to reduce rapidly degradable carbohydrates in rumen [12]. According to the latter, diverse options have been studied to cover two or more targets.

#### **3.1 Nonfibrous carbohydrates**

Carbohydrate fermentation is the main source of energy for the ruminant. Quantity and quality of rapidly degradable carbohydrates, usually known as nonfibrous carbohydrates (NFCs), depends on the feedstuff. Thus, NFCs contained in corn (*Zea mays*) are mostly starch, whereas, in molasses, NFCs are mainly composed by mono- and disaccharides. Depending on the NFC type and the supplied feedstuff, certain pathways for synthesis may be favored. For example, whether increases in the structural carbohydrates are observed, the propionate synthesis pathway is enhanced. This pathway is beneficial to the animal since it reduces methane synthesis [13]. Otherwise, an increase in mono- and disaccharides

decreases microbial protein synthesis through reductions in the abundance of ammonia-utilizing cellulolytic bacteria [14]. Moreover, high NFC concentrations tend to increase VFA production which could cause ruminal acidosis.

#### **3.2 Fibrous carbohydrates**

It has been demonstrated that increases in dry matter intake reduce methane production [15]. Moreover, increases in digestibility is expected in fibrous material whether it is fine ground, as well as augmentations in the passage rate through increases in the turnover rate. Therefore, if turnover rate is increased, the passage rate would also increase. Hence, through augmentations in the passage rate, microorganisms that possess a lower growth rate, such as protozoa and archaea, will defaunate, thus decreasing methane production [16]. Otherwise, digestibility and methane production could be increased by increasing the retention time [17]. Additionally, by increasing the intake above the minimum for maintenance, the animal methane production will arise proportionally. This phenomenon will provoke a reduction in methane production per production unity [18]. Therefore, an animal fed under a pasture basis will produce less methane as part of the GHG produced compared to an animal fed with a high-concentrate or high-fiber proportion diet.

#### **3.3 Bypass protein**

The protein contained in ruminants' feedstuffs could be divided into two groups: degradable rumen protein (DRP) and undegradable rumen protein (URP). The first is degraded in rumen, and it is used as a nitrogen source in the microbial protein synthesis; the second escapes from ruminal degradation and is transported to the lower tract where it is susceptible of being absorbed by the animal in the form of amino acids [19]. In spite of several reasons to name it bypass protein, one of the main characteristics is its low retention time in rumen or, the inverse action, the high passage rate. In the case of high passage rates, microorganisms which possess a low growth rate will tend to defaunate; this is the case of the methanogens. Thus, methanogenesis will be affected and methane production will be reduced. Nowadays, some secondary metabolites are identified as protein protectors, by forming complexes with proteins and avoiding their degradation in rumen. The latter allows proteins to go through the low tract and to be absorbed after liberating complexes due to the acidic pH in the intestine [20].
