Effects of Megasphaera elsdenii administration on performance and carcass traits of finishing Bos indicus feedlot cattle

This study evaluated the effects of Megasphaera elsdenii administration at the beginning of the feedlot period on performance of Bos taurus indicus bulls. On d 0, 383 Nellore bulls (initial shrunk body weight 384 ± 29.2 kg; initial age = 24 ± 2 mo) were assigned to treatments in a randomized complete block design. Treatments consisted of 1) 14 d adaptation diet and transition to a finishing diet (CONT), 2) CONT plus oral administration of 20 mL of Lactipro-NXT (M. elsdenii) on d 0 of the study (MEG-14), 3) CONT diet, consisting of 6 d of adaptation diet plus oral administration of 20 mL of Lactipro-NXT on d 0 of the study (MEG-6), and 4) No adaptation diet and oral administration of 20 mL of Lactipro-NXT on d 0 of the study (MEG-0). Experimental period lasted 119 d. No treatment effects were observed for any of the performance parameters evaluated herein (P ≥ 0.15). Nonetheless, a treatment × wk interaction was observed for DM, NEm, and NEg intakes (P < 0.0001). For all these parameters, MEG-0 and MEG-6 had a reduced intake vs. MEG-14 and CONT in the first wk of the study (P ≤ 0.05). For the carcass traits, no effects were observed for HCW (P ≥ 0.24), whereas MEG-6 had a greater REA when compared with MEG-0 and MEG-14 (quadratic effect; P = 0.04) and MEG-administered bulls tended to have a greater BFT vs. CONT (P = 0.08). In summary, M. elsdenii administration at the beginning of the feedlot period did not improve performance, whereas reducing the length of the adaptation period for 6 d improved REA of finishing Bos taurus indicus bulls.

True and Illusory Benefits of Modeling: Comment on “Genome-Scale Metabolic Network Reconstruction and In Silico Analysis of Hexanoic Acid Producing Megasphaera elsdenii. Microorganisms 2020, 8, 539”

Lee et al [...]

PSVI-15 Effect of direct-fed microbials on fecal characteristics during an acidosis induction

The objective was to investigate the effects of two direct-fed microbial dosing strategies on fecal characteristics of beef cattle during an acidosis challenge. Ruminal acidosis is a metabolic disorder in beef cattle that may contribute to hindgut acidosis. Eighteen ruminally cannulated steers (BW = 328 ± 20 kg) were used in a completely randomized design with 6 steers in each period. Two steers in each period were randomly assigned to one of three treatments: blank media (NCON), a single strain of Megasphaera elsdenii at 108 CFU (DFM1), and a combination of Megasphaera elsdenii and proprietary microbial strains at 1010 CFU per dose (DFM2). On d 1, DFM1 was dosed once and DFM2 and NCON were dosed daily at 0700 on d 1-15. A basal diet (45% forage) was fed ad libitum on d 1-7. To induce acidosis, steers were fasted for 24 h on d 8 and were fed the challenge diet (10% forage) ad libitum on d 9-15. Fecal pH was measured throughout the challenge and total feces was collected on d 11-14 to determine washed fecal particle size and observe mucin casts. Fecal pH and mucin cast score was not affected (P ≥ 0.29) by treatment. Fecal particle size in DFM1-treated steers was greater (P = 0.01) than NCON and DFM2. Fecal particle size tended (P = 0.06) to increase over time. Fecal particle size was not correlated (P ≥ 0.56) to ruminal or fecal pH. Fecal mucin cast score was positively correlated to dry matter intake (P < 0.01) and mean ruminal pH (P = 0.06). Mucin cast score may help in monitoring ongoing bouts of ruminal acidosis. Overall, results indicate direct-fed microbial treatment affected fecal particle size but not fecal pH and mucin cast score during an acidosis challenge.

Genome-Scale Metabolic Network Reconstruction and In Silico Analysis of Hexanoic acid Producing Megasphaera elsdenii

Hexanoic acid and its derivatives have been recently recognized as value-added materials and can be synthesized by several microbes. Of them, Megasphaera elsdenii has been considered as an interesting hexanoic acid producer because of its capability to utilize a variety of carbons sources. However, the cellular metabolism and physiology of M. elsdenii still remain uncharacterized. Therefore, in order to better understand hexanoic acid synthetic metabolism in M. elsdenii, we newly reconstructed its genome-scale metabolic model, iME375, which accounts for 375 genes, 521 reactions, and 443 metabolites. A constraint-based analysis was then employed to evaluate cell growth under various conditions. Subsequently, a flux ratio analysis was conducted to understand the mechanism of bifurcated hexanoic acid synthetic pathways, including the typical fatty acid synthetic pathway via acetyl-CoA and the TCA cycle in a counterclockwise direction through succinate. The resultant metabolic states showed that the highest hexanoic acid production could be achieved when the balanced fractional contribution via acetyl-CoA and succinate in reductive TCA cycle was formed in various cell growth rates. The highest hexanoic acid production was maintained in the most perturbed flux ratio, as phosphoenolpyruvate carboxykinase (pck) enables the bifurcated pathway to form consistent fluxes. Finally, organic acid consuming simulations suggested that succinate can increase both biomass formation and hexanoic acid production.