Effects of high condensed-tannin substrate, prior dietary tannin exposure, antimicrobial inclusion, and animal species on fermentation parameters following a 48 h in vitro incubation

Abstract

Condensed tannins (CT), prior dietary CT exposure, animal species, and antimicrobial inclusion effects on 48 h extent of in vitro fermentation were measured in an experiment with a 3 × 2 × 2 × 3 factorial arrangement of treatments. Treatments included species of inoculum donor (Bos taurus, Ovis aries, or Capra hircus; n = 3/species), prior adaptation to dietary CT (not adapted or adapted), culture substrate (low-CT or high-CT), and antimicrobial additive (none, bacterial suppression with penicillin + streptomycin, or fungal suppression with cycloheximide). Low-CT or high-CT substrates were incubated in vitro using inoculum from animals either not exposed (period 1) or previously exposed to dietary CT (period 2). The extent of IVDMD after 48 h of incubation was greater (P < 0.001) for cultures with low-CT substrate (21.5%) than for cultures with high-CT substrate (16.5%). Cultures with high-CT substrate or with suppressed bacterial activity had less (P < 0.001) gas pressure than cultures with low-CT substrate or cultures with suppressed fungal activity. Total VFA concentrations were greater (P < 0.001) in low-CT cultures when inoculum donors were without prior CT exposure (83.7 mM) than when inoculum was from CT-exposed animals (79.6 mM). Conversely, total VFA concentrations were greater (P < 0.001) in high-CT cultures with tannin-exposed inoculum (59.4 mM) than with nonexposed inoculum (52.6 mM). As expected, CT and suppression of bacterial fermentative activities had strong negative effects on fermentation; however, prior exposure to dietary CT attenuated some negative effects of dietary CT on fermentation. In our experiment, the magnitude of inoculum-donor species effects on fermentation was minor.

Figure 1.

Effects of incubation time and substrate CT content on IVDMD during a 48 h incubation. Low-CT substrate was Bromus inermis hay only (0.5 g; DM basis), and high-CT substrate was Bromus inermis hay (0.4299 g; DM basis) and quebracho tannin (0.0701 g; DM basis), which provided 10.1% CT in the substrate. Within incubation-time point, separation of error bars indicates difference between substrate types (P < 0.001; LSD = 3.69). Within low-CT substrate, means not bearing a common superscript letter of a, b, or c differ between incubation-time points (P < 0.001; SEM = 2.15). Within high-CT substrate, means not bearing a common superscript letter of d, e, or f differ between incubation-time points (P < 0.001; SEM = 2.15).

Figure 2.

Effects of antimicrobial additive and prior dietary CT exposure on total VFA concentration following a 48 h in vitro incubation (LSD = 8.51; SEM = 2.329). Penicillin + streptomycin = 0.40 mg penicillin (1,600 U/mg) and 0.064 mg streptomycin sulfate (720 IU/mg) per mL of culture to act as a suppressant to bacterial fermentative activities. Cycloheximide = 0.16 mg cycloheximide per mL of culture to act as a suppressant to fungal fermentative activities. No prior CT exposure = inoculation with ruminal fluid from animals fed a tannin-free diet. Prior CT exposure = inoculation with ruminal fluid from animals fed a high-CT diet. Means not bearing a common superscript letter differ (P = 0.001).

Figure 3.

Effects of substrate CT content, antimicrobial additive, and prior dietary CT exposure on propionate concentration following a 48 h in vitro incubation (LSD = 3.7; SEM = 0.77). Low-CT substrate was Bromus inermis hay only (3.067 g; DM basis), and high-CT substrate was Bromus inermis hay (2.637 g; DM basis) and quebracho tannin (0.43 g; DM basis), which provided 10.1% CT in the substrate. Penicillin + streptomycin = 0.40 mg penicillin (1,600 U/mg) and 0.064 mg streptomycin sulfate (720 IU/mg) per mL of culture to act as a suppressant to bacterial fermentative activities. Cycloheximide = 0.16 mg cycloheximide per mL of culture to act as a suppressant to fungal fermentative activities. No prior CT exposure = inoculation with ruminal fluid from animals fed a tannin-free diet. Prior CT exposure = inoculation with ruminal fluid from animals fed a high-CT diet. Means not bearing a common superscript letter differ (P < 0.001).