In recent decades, some studies were conducted to illustrate the new scope in the field of probiotics and to discover the potential probiotic microbes. According to Sun et al., (2021) multi-species probiotics consisting of
L. acidophilus, L. casei,
B. thermophilum, and
E. faecium were successfully used to reduce the diarrhea caused by enterotoxigenic
E. coli (ETEC) F18
+ in newly weaned pig
[18]. In addition, multi-species probiotics were helpful in enhancing growth performance through a reduction in intestinal inflammation, oxidative stress, and morphological damages. Sobrino et al. (2021) attempted to study AM substitutes in pig production. They used
Ligilactobacillus salivarius strain retrieved from sow’s milk and fed it to pregnant sows and piglets. The results suggested that there was a notable reduction in the presence of antibiotic-resistant
Lactobacillus, which became apparent in the treatment group
[19]. In recent studies, it was suggested that
Prevotella exerted positive consequences in pig production by enhancing growth performance and immune response
[20][21][22][23]. The
Lactobacillus, Escherichia, Shigella, and
Bacteroides dominate the small intestine microbiota, while on the other hand, the
Prevotella dominates the large intestinal microbiota during the newborn stage. Furthermore, the
Prevotella dominates the pig’s small and large intestines after weaning
[24]. Additionally, it was reported that the non-diarrheic piglets were found to have a considerably higher abundance of intestinal
Prevotella than diarrheic piglets.
Prevotellacea UCG-003 was the key bacterium in the non-diarrheic microbiota of piglets, according to co-correlation network analysis
[23]. Ngo et al. (2021) used a new probiotic (
B. amyloliquefaciens H57) in high concentrate feed pellets that reduces volatile fatty acid production and prevents flavor in pellet feed. That facilitates higher feed intake in ruminant animals
[25]. In recent studies on anaerobic fungi, it was demonstrated that it contributes essentially to ruminal fiber utilization by degrading plant cell walls in two ways, i.e., enzymatically and mechanically
[26][27]. Remarkably, ongoing exploration showed the affinity of fungal CAZymes for stubborn fiber, which might clarify the specific use of anaerobic fungi when lower quality forages were fed to ruminants. Therefore, this can also be used as a potential probiotic in ruminant nutrition
[28]. Studies on the utilization of
B. subtilis as a spore-shaping probiotic bacterium in livestock nutrition have shown no unsafe impacts and have exhibited the viability of its utilization as a probiotic, mostly because of its demonstrated AM, mitigating cell reinforcement and exhibiting enzymatic, and immunomodulatory action
[29]. A study by Cai et al. (2021) enumerated that
S. cerevisiae and
C. butyricum and their blend enhanced rumen conditions by expanding the pH and diminishing oxidation and upgraded rumen maturation capacities by expanding absorbability of supplements and further developing VFA production; from that point on, further enhancements in production growth of heat-stressed goats were observed
[30]. The
Debaryomyces hansenii is also gaining attraction as a new potential probiotic for both terrestrial and aquatic animals. The oral delivery of
D. Hansenii has been linked to probiotic features, such as immunostimulatory effects, gut microbiota regulation, increased cell proliferation, differentiation, and improved digestive function. Its bioactive molecules have been identified and linked to its immunomodulatory effect, including cell wall components and polyamines
[31]. Therefore, there are many potential probiotic microbes that are still to be discovered, which might play an evolutionary role in livestock production.