Feed Efficiency and Rumen Fermentation

Dear Colleagues,

Rumen fermentation is the main biological process that determines how efficiently ruminants convert feed into metabolizable nutrients, and its dynamics directly influence energy extraction, protein utilization, and overall animal performance. Feed efficiency depends on the coordinated action of rumen microorganisms that ferment NDF, degrade proteins, and transform these nutrients into volatile fatty acids. Forages provide structural carbohydrates that stimulate chewing and saliva secretion, improving the buffering capacity and supporting cellulolytic bacteria responsible for fiber digestion. Concentrates rich in starch and soluble carbohydrates increase the energy density of the diet and promote rapid fermentation, often increasing propionate production and decreasing methane emissions. High-quality forages enhance microbial activity and promote stable fermentation. However, excessive concentrates can depress rumen pH, inhibit fiber-digesting microbes, and lead to ruminal acidosis. Thus, the forage-to-concentrate ratio must be carefully managed to balance energy supply with rumen stability. In this context, feed additives provide additional tools to modulate rumen fermentation and enhance efficiency.

Protein degradation in the rumen also plays a crucial role in feed efficiency. Microbial protein synthesis represents the primary source of amino acids for the animal once digested in the small intestine. Efficiency improves when the supply of rumen-degradable protein matches microbial needs and when rumen-undegradable protein provides additional amino acids without excessive nitrogen loss. Synchronizing protein degradation with carbohydrate fermentation is essential; if protein degrades too rapidly without sufficient fermentable energy, ammonia accumulates and is converted to urea, representing a loss of nitrogen and energy.

We invite researchers, academics, and industry specialists to submit original research articles, reviews, and short communications for this Special Issue in Fermentation dedicated to emerging insights and innovations in rumen fermentation and feed efficiency in ruminant nutrition.

In this Special Issue, research areas may include the following topics:

• Rumen microbiome composition and its role in feed efficiency;
• Fermentation dynamics of structural vs. non‑structural carbohydrates;
• Forage‑to‑concentrate ratio and rumen stability;
• Physical effectiveness of fiber and rumen buffering mechanisms;
• Methane mitigation strategies in ruminant nutrition;
• Feed additives as modulators of rumen fermentation;
• Synchronization of rumen‑degradable protein and fermentable carbohydrates;
• Rumen‑undegradable protein and amino acid supply to the small intestine;
• Nutritional factors affecting ammonia accumulation and nitrogen recycling;
• Impact of forage quality on rumen fermentation and animal performance.

I look forward to receiving your contributions.

Prof. Dr. Stefanie Alvarenga Santos
Guest Editor

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