**7. Other feedstuffs**

Since the 1970s, ruminal microbes and their effect on ingested nutrients have been subject of intensive research [27]. Ruminal microorganisms are crucial for the digestive performance of animals. Addition of feedstuffs in diets of ruminants has led to investigate their effects on the absorption and utilization of nutrients as well as the ruminal environment and conditions. Genetically modified *Escherichia coli* showed a ruminal methanogenesis mitigation effect in sheep [62]. Other researches [63] reported that *Lactococcus lactis* produces nisin, which has demonstrated antimicrobial activity against Gram-positive bacteria, resulting in a mitigation effect on ruminal methane emission.

β1–β4 galacto-oligosaccharides (GOS), along with glucose, fructose, and starch, present in the rumen are used by *Bifidobacterium* and *Lactobacillus* as substrates to produce lactate and acetate. Lactate is one of the main transitional compounds during propionate production, which competes against methanogens for available hydrogen. As a result, methane production can be decreased by GOS consumption [64].
