**1. Introduction**

The world's population have substantially increased in the last decades, and it is expected to keep increasing for the next 30 years until the population reaches 9.8 billion in 2050 [1]. Consequently, there is a growing demand for food and natural resources for human surviving. Livestock represents a main source of protein and energy for human consumption, as well as an important basis of financial revenues for families at rural areas. However, this economic activity is positively correlated to the climate change (CC) effect [2]. In the last centuries, CO2 and NO2 emissions have increased 31 and 16%, respectively; whereas, methane has increased twofold. Approximately, 40% of the methane emitted to atmosphere is originated from natural sources [2]; the remaining 60% is originated from anthropogenic sources (livestock, rice crops, fossil fuel exploitation, and dump).

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

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.
