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Assessment of the effect of plant tannins on rumen fermentation and gut microbial diversity in goats using 16S rDNA amplycon pyrosequencing
Two grazing experiments were performed to 1) investigate the effects of supplementing condensed tannins (CT)-containing pine bark (PB) powder on ADG, ruminal fermentation, and gut microbial diversity dynamics, and 2) to quantify the influence of different sources of tannins supplementations on ruminal fermentation and gut microbial diversity changes of goats grazing winter pea and ryegrass dominant forages. In Exp. 1, 20 Kiko cross male goats (Capra hircus; initial BW = 39.7 ± 2.55 kg) were randomly assigned to 2 experimental diets (alfalfa pellet vs. PB powder). Alfalfa pellet (no CT as a control) or PB (11% CT) was supplemented at 0.8% BW for targeted total DMI of 1.2% BW. The remainder DMI of each diet was obtained from grazing for 60 d. In Exp. 2, 12 Kiko cross goats were used to measure ADG, ruminal fermentation, and gut microbial population in the rumen of goats grazing bermudagrass. The animals were randomly assigned to 3 experimental diets: 1) no tannins (control), 2) chestnut extract at 100 g/d (CTE), and 3) quebracho CT extract at 100 g/d (QCTE). In Exp. 1, ADG was greater (P < 0.05) in PB (209 g/d) than the control (188 g/d). However, goats grazing winter pea and ryegrass forages with PB supplementation decreased (P < 0.05) concentrations of acetate (14.4 vs. 15.1 mM), propionate (3.34 vs. 3.83 mM), butyrate (1.82 vs. 2.00 mM), and total VFA (22.5 vs. 23.7 mM) compared to those in the control, respectively. Bacterial population in PB-supplemented group was greater for Bacteroides (20.5 vs. 33.2%), Firmicutes (67.2 vs. 57.3%), and Proteobacteria (1.15 vs. 1.44%) phylum compared with control group, respectively. In Exp. 2, ADG was greatest for CTE (275 g/d) than QCTE (148 g/d) and the control (79.4 g/d). Goats grazing bermudagrass pasture with CTE had greater (P < 0.05) concentrations of acetate, propionate, butyrate, and total VFA compared to those in QCTE and control. Bacterial population in CTE-supplemented group was greatest for Bacteroides (51.5, 52.9, and 35.3%), Firmicutes (40.2, 36.7, and 55.9%), and Proteobacteria (2.28, 2.18, and 1.49%) phylum compared with QCTE and control group, respectively. Rumen archaeal population, however, was greatest in control group (0.70%) compared with CTE (0.23%) and QCTE (0.22%) group. Supplementing tannins in goat diets such as CTE, QCTE, or PB powder has the potential to improve ADG and modify rumen bacterial and archael population.
Keywords: goats, gut microbial diversity, tannins