𝘔𝘦𝘨𝘢𝘴𝘱𝘩𝘢𝘦𝘳𝘢 𝘦𝘭𝘴𝘥𝘦𝘯𝘪𝘪

Introduction

One of the primary challenges in ruminant nutrition is the risk of ruminal acidosis, a condition characterized by a drop in rumen pH due to the overproduction of lactic acid. This often occurs when animals consume high-concentrate diets, such as grains, leading to digestive upset, reduced feed intake, and decreased performance (Nagaraja & Titgemeyer, 2007; Aikman et al., 2011). Megasphaera elsdenii (M. elsdenii), a lactate-utilizing bacterium (LUB), has emerged as a promising direct-fed microbial (DFM) for mitigating subacute ruminal acidosis (SARA) and enhancing animal performance (Cabral & Weimer, 2024; Mazon et al., 2025). Unlike other lactate-metabolizing bacteria, such as Selenomonas ruminantium, M. elsdenii uniquely utilizes both D- and L-lactate isomers due to its lactate racemase (LR) enzyme, enabling efficient lactic acid clearance (Susanto et al., 2023). This review synthesizes current research on M. elsdenii's role in rumen health, feed efficiency, methane mitigation, and growth performance.

Mechanisms of Action

M. elsdenii’s metabolic activity centers on lactate conversion to volatile fatty acids (VFAs), primarily propionate, via the acrylate pathway (Counotte et al., 1981; Prabhu et al., 2012). The LR enzyme, induced by lactate availability, allows preferential lactate metabolism over glucose, stabilizing rumen pH during high carbohydrate feeding (Hino & Kuroda, 1993; Cabral & Weimer, 2024). M. elsdenii prevents SARA and supports microbial balance by reducing lactic acid accumulation, though its effects on total bacterial and protozoal populations remain inconsistent (Klieve et al., 2003; Susanto et al., 2023).

Effects on Feed Intake

M. elsdenii’s impact on dry matter intake (DMI) is context-dependent. Supplementation increases solid feed DMI in calves during the weaning and post-weaning phases, likely due to enhanced rumen development (Mazon et al., 2025). Similarly, lambs transitioning to concentrate diets exhibit improved DMI when pre-treated with M. elsdenii (Direkvandi et al., 2020). Conversely, some studies report reduced DMI, potentially linked to propionate-induced satiety (Elsden & Lewis, 1953; Susanto et al., 2023). Variability in responses may stem from differences in strain efficacy, dosage, and dietary composition (Drouillard et al., 2012; Cabral & Weimer, 2024).

Feed Efficiency and Growth Performance

Meta-analyses indicate that supplementation with M. elsdenii improves feed efficiency by 19.7%, primarily due to enhanced nutrient utilization and reduced dry matter intake DMI (Susanto et al., 2023). Calves administered M. elsdenii show greater average daily gain (ADG) and rumen papillae development, which are important for post-weaning performance (Muya et al., 2015; Mazon et al., 2025). In feedlot steers, M. elsdenii accelerates adaptation to high-concentrate diets, boosting ADG by 5.6% (Leeuw et al., 2009; Drouillard et al., 2012). However, dairy studies report mixed outcomes, with no significant milk yield improvements in some trials (Aikman et al., 2009; Hagg et al., 2010).

Rumen Fermentation and Methane Mitigation

M. elsdenii consistently reduces ruminal lactate and stabilizes pH, which is crucial for SARA prevention (Kung & Hession, 1995; Arik et al., 2019). In addition, propionate production increases, altering VFA profiles and potentially reducing methane emissions via hydrogen diversion (Prins & van der Meer, 1976; Susanto et al., 2023). While some studies report a linear decrease in methane output (Jayanegara et al., 2014), others did not find significant changes, highlighting the need for further mechanistic research (Chen et al., 2019).

Carcass Characteristics and Health Benefits

Carcass weight and gain improvements are observed in Bos indicus cattle supplemented with M. elsdenii (Lopes et al., 2021). However, effects on marbling and fat deposition remain inconsistent (Miller, 2023). Health benefits include reduced diarrhea, bloat, and liver abscess incidence, though outcomes vary with diet and administration timing (Nagaraja et al., 1999; Susanto et al., 2023).

Conclusion

M. elsdenii demonstrates potential as a probiotic for optimizing rumen health, feed efficiency, and methane mitigation in ruminants. However, its efficacy is influenced by strain selection, dosage, and dietary factors. Future research should prioritize strain-specific effects, long-term microbiome impacts, and standardized protocols to maximize benefits in diverse production systems.

References

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