Inside the rumen: Phages, feed and future dairy nutrition

Want to see how tiny viruses could reshape dairy nutrition? We sit down with Dr. Hugo Monteiro of the University of California-Davis to explore the unseen forces inside the rumen and how they tie directly to feed efficiency, milk production, and methane reduction. His work connects residual feed intake (RFI), microbial ecology, and host genetics into a framework that makes efficiency measurable and actionable.We start by clarifying why RFI outperforms traditional metrics: it isolates true biological efficiency independent of milk yield and body condition. From there, we dive into the rumen as a dynamic battlefield where bacteriophages constantly prune and empower bacterial populations. That “phage pressure” appears stronger in efficient cows, selecting microbes that better harvest energy, recycle nitrogen, and produce bioactive molecules. Some of those molecules may stimulate growth hormone and other anabolic pathways, hinting at a physiological bridge between microbial signals and performance at the udder.Dr. Monteiro explains how lower gut microbiomes act as a proxy for undigested substrates, providing a window into what the rumen missed. He also shares evidence that efficient cows absorb more key precursors even when rumen concentrations look similar, underscoring a genetics-by-microbiome interaction. On the practical side, we cover deep sequencing to profile microbial protein amino acids, rethinking RUP screening, and precision strategies for rumen-protected amino acids. We map near-term gains producers can use today and look ahead to phage-based tools and microbiome editing that could arrive within five to ten years, including prospects for targeting methanogens to cut emissions.Dr. Monteiro was a speaker at the recent 2025 Kemin Intestinal Health. Visit kemin.com/symposium to learn more and to view Dr. Monteiro’s presentation and more in on-demand.