FROM THE FARM REPORT: MICROBIAL PROTEIN: A HIDDEN ALLY IN CALF NUTRITION
- Marcos Marcondes
- May 27
- 3 min read
A recent breakthrough in calf nutrition science is changing how we think about protein supply in pre-weaned ruminants. A study led by researchers from the Federal University of Viçosa, Brazil and Miner Institute has delivered the first quantification of microbial crude protein (MCP) synthesis in the immature rumen of pre-weaned animals fed different amounts of milk replacer. This research shines new light on the metabolic capacity of the young rumen and opens the door to innovative feeding strategies for early-life growth and development.
Traditionally, it was believed that milk — and especially milk replacer — bypassed the rumen entirely, funneled through the esophageal groove into the abomasum for enzymatic digestion. But what happens when some of that liquid diet "leaks" into the rumen? Instead of being wasted or causing metabolic issues, it turns out this leakage may support a nascent microbial population capable of synthesizing valuable microbial protein.
The study, published in the Journal of Dairy Science (https://doi.org/10.3168/jds.2024-25695), involved 60 dairy goat kids fed either a low (1 L/day) or high (2 L/day) allowance of milk replacer. Remarkably, an average of 56% of the liquid diet entered the rumen, where it supported fermentation and microbial growth — even in the absence of starter feed. Researchers quantified microbial protein synthesis using DNA-based methods and showed that young animals are already producing nearly 2 grams/day of MCP at just 45 days of age. Although this amount may seem modest, the proportion of MCP relative to nitrogen intake varied considerably — from 7% to 12% among individuals. This high variability underscores the potential for nutritional or additive-based strategies to further enhance MCP production in pre-weaned animals, opening new opportunities to support early rumen development and improve protein efficiency.
While this may seem small, the implications are large. MCP is not just another protein source — it has a highly digestible amino acid profile and supports lean tissue growth. More importantly, it helps prime the calf's digestive system for future solid feed fermentation, laying the groundwork for efficient nutrient absorption and improved performance post-weaning.
What’s novel here is the demonstration that milk replacer itself — not just starter feed — can fuel microbial protein production if some portion reaches the rumen. This could reshape how nutritionists design feeding programs. Until now, calf models like those from NASEM (2021) have excluded MCP from metabolizable protein calculations for pre-weaned animals. But this study offers a compelling argument for its inclusion.
Looking ahead, this opens the door to a new generation of feed additives. If the microbial ecosystem in the young rumen is functional, why not nourish it intentionally? Products like targeted probiotics, prebiotics, or rumen-specific amino acid blends could be added to milk replacers or early starter feeds to enhance microbial growth, MCP output, and rumen development. Such additives might improve growth rates, immune responses, and transition to weaning — all without relying solely on solid feed intake.
The future of calf nutrition is no longer just about what reaches the small intestine. As this study proves, what happens in the rumen — even in its earliest days — can make a lasting difference. And by harnessing that microbial potential we may help calves grow into healthier, more efficient cows.
— Marcos Marcondes
