**4. Feed additives**

Some strategies are focused on providing feed additives to modify the presence or absence of methanogens, protozoa, or the direct or indirect inhibition of ruminal methanogenesis [21]. By supplementing feed additives, good results are observed in methane production and productive performance. These strategies imply the use of high nutritive quality forages, organic acids, ionophores, probiotics, vegetable extractives, and secondary metabolites from different plants [22]. However, the most used are presented and briefly discussed:

• *Ionophores*: Ionophores are additives which possess a proved antimicrobial effect on some ruminal and cultivable strains, especially gram-positive bacteria [23]. Ionophore compounds like monensin and lasalocid have demonstrated to modify rumen fermentation and decrease methane emissions. The latter can be elucidated due to the fact that ionophores, as mentioned earlier, present

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

• *Homoacetogens*: Homoacetogens are a group of acetate-producing bacteria which can convert carbon dioxide into acetate using hydrogen [26]. The acetogenesis is a competitive pathway against methanogenesis for hydrogen use. Additionally, the production of ruminal acetate can be used as an energy source for the animal [27]. However, the thermodynamics of the reactions are more favorable to methanogenesis, and the use of ruminal homoacetogens as

additives did not suppress methanogenesis in all the studies [28, 29].

due to a change in methanogens population [32].

nia-utilizing bacteria [36].

• *Essential oils*: The effect of the addition of some essential oils into methanogenesis is through the capture of hydrogens in the biohydrogenation process of unsaturated fatty acids in the rumen [30]. Likewise, some medium-chain fatty acids contained in vegetable oils have demonstrated suppression of methanogenesis through the reduction of methanogens and ciliate [31]. In addition, some authors stated that the methanogenesis suppression with coconut oil was

• *Yeast cultures*: The most used yeast culture in livestock research is *Saccharomyces cerevisiae*, and it has been used as a fermentation modifier [23]. Additionally, yeast cultures have been used as rumen fermentation modifiers and promoters of microbial growth [33]. In fact, rumen fibrolytic bacteria have a clear preference for a nitrogen source for ammonia production, and this is enhanced by yeast cultures for microbial protein synthesis [34]. Moreover, recent reports have suggested the stabilization of pH through a decrease in lactate production when using in vitro yeast cultures [35]. Thus, the antimethanogenic action is suggested through the improvement of fiber digestion and increasing ammo-

• *Others*: Vaccination and the use of bacteriophages are a different alternative for methane mitigation. Hence, vaccines against methanogens like

suggested by other authors as a strategy for methane abatement [22].

for a higher feed production, converting animal feeding production into a natural competitor for human feeding production in the search for arable lands. Consequently, diverse researches have focused into trying different forage sources which were not conventional as animal feeding before but now could be considered as alternative forage sources [38, 39]. Nonconventional forages include a wide variety of perennial plants and agriculture and commercial by-products

**5. Conventional and nonconventional forage sources**

*Methanobrevibacter* spp. have been applied to sheep presenting methane reductions of 7.7% [37]. Likewise, the use of phagaes against rumen archaea has been

As expressed before in this chapter, the increasing global population demands

affinity to hydrogen- and formate-producing, butyrate-producing, lactate-producing, and ammonia-producing bacteria, all of them gram-positive. However, succinate- and propionate-producing bacteria are resistant to ionophores [24]. Hence, it is assumed that reductions in the methanogenesis pathway are due to the hydrogen capture by propionate-producing bacteria, limiting methanogenesis through the restriction of hydrogen availability in the CO2 reduction pathway. Unfortunately, prolonged use of monensin in steers has shown a loss of methanogenesis inhibition action and a resistance of bacteria to these

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

antibiotics [25].

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

affinity to hydrogen- and formate-producing, butyrate-producing, lactate-producing, and ammonia-producing bacteria, all of them gram-positive. However, succinate- and propionate-producing bacteria are resistant to ionophores [24]. Hence, it is assumed that reductions in the methanogenesis pathway are due to the hydrogen capture by propionate-producing bacteria, limiting methanogenesis through the restriction of hydrogen availability in the CO2 reduction pathway. Unfortunately, prolonged use of monensin in steers has shown a loss of methanogenesis inhibition action and a resistance of bacteria to these antibiotics [25].

