A core microbiota of the gastrointestinal tract of pigs has been reported to contain 2 predominant phyla; Firmicutes and Bacteroidetes (Holman et al, 2017).
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Bacteroidetes phylum is composed of gram-negative bacteria, whereas Firmicutes phylum is composed of gram-positive bacteria species (Gomes et al., 2014). The composition and distribution of microbiome in the hindgut of conventional pigs have been investigated. Kim et al. (2011) determined bacterial diversity in the feces of commercial pigs fed antibiotic-free corn-soybean meal based-diets from 10 to 16 weeks of age, and observed that Prevotella, Anaerobacter, Streptococcus,
Lactobacillus, Coprococcus, Sporacetigenium, Megasphaera, Subdoligranulum, Blautia, Oscillibacter, Faecalibacterium, Pseudobutyrivibrio, Dialister, Sarcina, and Roseburia were the most abundant genera found in feces of pigs, accounting for more than 59% of the total sequences at the genus level. Of these 15 abundant genera, Prevotella was the only genus belonging to Bacteroidetes. Prevotella was the most abundant genus at the initiation of the study and its relative abundance reduced as pigs matured. Anaerobacter was the most abundant genus at the termination of the study and its relative abundance increased as pigs aged. Holman et al. (2017)
conducted a meta-analysis to determine a core microbiota for commercial pigs using 20 published data sets, and observed that Clostridium, Blautia, Lactobacillus,
Prevotella, Ruminococcus, Roseburia, and Subdoligranulum were the most abundant genera found in fecal samples regardless of country of origin, diet, age or breed of pigs. Of these 7 abundant genera, Prevotella was the only genus that belongs to Bacteroidetes. Guevarra et al. (2015) determined gut microbiota composition in the feces of commercial white breed pigs (Landrace) and black breed pigs (a breed line of domestic pigs developed in South Korea) fed corn-soybean meal-based diets from 3 to 12 weeks of age, and observed that Prevotella and Treponema were the 2 genera that were most abundant in feces of white breed pigs, whereas Prevotella
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predominated in feces of black breed pigs. In feces of white breed pigs, Firmicutes, Bacteroidetes, and Spirochaetes were the dominant phyla, accounting for 95% of the total sequences at the phylum level, whereas Firmicutes and Bacteroidetes
predominated in feces of black breed pigs. Allen et al. (2011) determined bacterial diversity in the feces of commercial pigs fed corn-soybean meal based-diets from 3 to 13 weeks of age, and observed that Prevotella, Oscillibacter, Treponema,
Clostridium, and Streptococcus were the most abundant genera found in feces of pigs, accounting for more than 81% of the total sequences at the genus level. Of these 5 abundant genera, Oscillibacter, Clostridium, and Streptococcus were belonging to Firmicutes. From these studies, it appears that the most abundant phylum of
microorganisms in the gastrointestinal tract of pigs fed corn-soybean meal-based diets is Firmicutes, and that Streptococcus, Lactobacillus, Oscillibacter, and Clostridium are the predominant genera of microbes present in the lower gastrointestinal tract of pigs fed corn-soybean meal-based diets regardless of country, origin, age or breed of pigs.
The effects of including canola meal in diets for pigs on hindgut microbial communities have been reported. Mejicanos et al. (2017) included 20% of canola meal in diets for nursery pigs that had weaned at 21 d of age, and observed a 108 % increase in the relative abundance of Lactobacillus and a 47, 39, and 37% decrease in the relative abundance of Bifidobacterium, Enterococcus, and Clostridium Custer IV (Clostridium, Eubacterium, Ruminococcus and Anaerofilum genera), respectively, in feces of nursery pigs at 21 d post-weaning. Of these abundant genera, Lactobacillus, Enterococcus, Clostridium, Eubacterium, Ruminococcus, and Anaerofilum were the abundant genera belonging to Firmicutes, whereas Bifidobacterium was the only
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genus belonging to Actinobacteria. Also, Velayudhan et al. (2018) reported a 266 and 177% increase in the relative abundance of Lactobacillus and Enterococcus,
respectively, in feces of gestating sows on day 90 of gestation due to an increase in the level of fiber (NDF) from 88 to 132 g/kg and total glucosinolates from 0 to 2.73 àmol/g through dietary inclusion of canola meal. Wu et al. (2019) determined microbial communities in the colon of mice fed cornstarch-based diets from 10 to 11 weeks of age, and observed a 12 and 5% increase in the relative abundance of Firmicutes and Bacteroidetes, respectively, in the colon of mice due to dietary inclusion of raw broccoli at 10%. They also observed a 14 and 9% increase in the relative abundance of Firmicutes and Bacteroidetes, respectively, in the colon of mice due to dietary inclusion of hydrolyzed broccoli at 10%. From these studies, it appears that dietary glucosinolates increase the relative abundance of Firmicutes in the gastrointestinal tract of animals. However, the mechanisms by which dietary
glucosinolates could increase the abundance of Firmicutes in the gastrointestinal tract have not been reported.
Gastrointestinal tract microbiota composition is strongly correlated with body weight. For instance, Ley et al. (2006) reported a reduction in Firmicutes to
Bacteriodetes ratio in the gastrointestinal tract of obese humans due to a reduction in body weight. Ley et al. (2005) also reported a higher Firmicutes to Bacteriodetes ratio in obese mice than in lean mice. Also, Armougom et al. (2009) reported a greater relative abundance of Lactobacillus genus (belongs to Firmicutes) in feces of obese individuals than in feces of lean individuals. In the same study, the relative abundance of Bacteroidetes was lower in feces of obese individuals than in feces of lean
individuals. Thus, the increased abundance of Firmicutes and Bacteriodetes is
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associated with BW gain and weight loss, respectively. This is because Firmicutes is more efficient than Bacteroidetes with regard to the extraction of energy from diets, leading to greater availability of energy in the host harboring the former than the latter microorganisms (Kallus and Brandt, 2012). Thus, the presence of canola co-products- derived glucosinolates in diets for pigs is expected to result in an increase in the abundance of microorganisms that promotes weight gain.