Hidden Rumen Secrets of Tropical Cattle Feeds Revealed by Cornell Fractionation System

In the humid tropics of South Asia, millions of smallholder dairy farmers feed their cattle rations built from a familiar cast of ingredients: maize, soybean meal, coconut oil cake, rice bran, wheat bran and a scattering of agro-industrial by-products. Yet a new study from Kerala Veterinary and Animal Sciences University shows that two feeds with nearly identical crude protein or total carbohydrate content can behave in radically different ways inside the rumen, the fermentation vat that drives nearly all of a cow’s nutrition. The finding, published in the journal Discover Animals, could reshape how nutritionists across the tropics formulate cattle diets.

The research team, led by Lasna Sahib, applied the Cornell Net Carbohydrate and Protein System, or CNCPS, to thirteen concentrate ingredients routinely used in feed mills across India. Rather than reporting only crude protein and crude fibre, the CNCPS partitions every feed into fractions defined by how fast they degrade in the rumen. Carbohydrates are split into rapidly fermentable sugars and organic acids (CA), intermediately degradable starch and pectins (CB1), slowly fermentable available cell wall (CB2), and lignin-bound cell wall that is essentially indigestible (CC). Proteins are similarly divided into non-protein nitrogen (PA), rapidly, intermediately and slowly degradable true protein (PB1, PB2 and PB3), and acid detergent-insoluble protein that no enzyme in the animal can reach (PC).

The biological logic behind this framework is what gives it its predictive power. Rumen microbes, the organisms that actually convert feed into meat and milk, need fermentable energy and degradable nitrogen to arrive at roughly the same time. When they do, microbial protein synthesis is maximised and the animal receives a steady supply of high-quality protein downstream. When they do not, nitrogen is wasted as ammonia and excreted in urine, or energy is lost as heat and gas. The CNCPS was designed to capture exactly this synchronisation problem, and when its inputs have been properly measured it has explained around 90 per cent of the variation in individual cow milk production with a bias of only 1.3 per cent.

Despite that track record, the system’s standard feed library was built largely from temperate feedstuffs. Comprehensive fractionation data for the concentrates that dominate South Asian rations, including regionally distinctive by-products such as tapioca starch waste, black gram husk and alfalfa residue, have been scattered across small studies or missing altogether. To fill the gap, the Kerala team procured six independent consignments of each of the thirteen ingredients from commercial suppliers, analysed every sample in duplicate, and expressed the results as means with standard errors. The protein concentrates included alfalfa residue, coconut oil cake, sesame oil cake, groundnut cake, soybean meal, sunflower cake and corn gluten feed; the energy concentrates were maize, de-oiled rice bran, wheat bran, rice polish, tapioca starch waste and black gram husk.

The carbohydrate results expose how misleading a single number can be. Maize, the region’s staple energy feed, was dominated by the intermediately degradable starch fraction, with CB1 accounting for 71.53 per cent of its total carbohydrate, confirming its role as the primary fermentable energy source for ruminants. Rice polish, by contrast, carried a staggering 67.43 per cent of its carbohydrate in the unavailable CC fraction, meaning nearly two-thirds of the carbohydrate it contains can never be digested by the animal, no matter what the total carbohydrate figure suggests. Coconut oil cake and sesame oil cake fared similarly, with CC fractions of 58.42 and 52.70 per cent respectively, driven by their high lignin contents of 27.13 and 38.99 per cent of neutral detergent fibre.

Those lignin-bound fractions have direct practical consequences. Oilcakes that look respectable on a proximate analysis sheet may contribute far less fermentable energy than their composition implies, and rations that lean on them heavily must be supplemented with more fermentable sources to keep rumen microbes working. On the other side of the ledger, alfalfa residue and corn gluten feed carried high slowly fermentable fibre fractions, 63.22 and 58.54 per cent of carbohydrate respectively, the kind of structural carbohydrate that stabilises rumen pH and sustains microbial protein synthesis without the acidosis risk that comes with rapidly fermentable starch-heavy diets. Black gram husk and tapioca starch waste, both cheap milling by-products, turned out to supply readily fermentable energy, with fast-degrading CA fractions of 33.87 and 25.47 per cent of carbohydrate.

The protein picture was equally revealing. Soybean meal, the benchmark protein supplement, was dominated by the intermediately degradable true protein fraction PB2 at 78.91 per cent of crude protein, closely matching European data. Alfalfa residue, which in this study refers to the leaf-derived protein concentrate left after chlorophyll extraction rather than ordinary alfalfa hay, was dominated by the slowly degradable PB3 fraction at 75.08 per cent of crude protein, making it a natural source of protein that escapes rumen breakdown. Groundnut cake released nitrogen quickly, with 44.48 per cent of its crude protein in the rapidly degradable PB1 pool, while corn gluten feed was extraordinary in a different way: 68.47 per cent of its crude protein was non-protein nitrogen, with 98.56 per cent of its soluble protein consisting of NPN, a signature of wet milling processes that break true protein down into ammonia and peptides.

That corn gluten feed profile carries a warning. High non-protein nitrogen supply without synchronously available fermentable carbohydrate drives ammonia accumulation and urinary nitrogen losses, so the PA-to-CB1 balance becomes critical when the ingredient is included in a ration. Pairing it with a high-starch energy source such as maize is precisely the kind of matching the CNCPS is built to guide. Another cautionary figure came from tapioca starch waste, where 45.73 per cent of crude protein sat in the heat-damaged PC fraction, bound in Maillard reaction products that neither rumen microbes nor the animal can use. The authors note that because the ingredient contains only 2.61 per cent crude protein to begin with, the absolute amount of damaged protein is nutritionally negligible, but the same PC logic cautions against overestimating the metabolisable protein contribution of black gram husk and de-oiled rice bran, whose PC fractions were 11.95 and 7.71 per cent of crude protein.

When the team converted the protein fractions into rumen-degradable and rumen-undegradable protein using degradation and passage rate equations, the thirteen feeds spanned a nutritionally actionable spectrum. Corn gluten feed delivered the highest rumen-degradable protein at 74 per cent of crude protein, making it best suited to rations where maximising microbial protein synthesis is the goal, particularly alongside high-CB1 energy sources. Coconut oil cake sat at the opposite extreme, with 64 per cent of its protein escaping rumen degradation, making it most valuable where post-ruminal amino acid supply is the limiting factor, as in early lactation or high-producing cattle whose metabolisable protein requirements exceed what microbes alone can supply. Soybean meal and alfalfa residue occupied an adaptable middle ground.

None of these distinctions are visible in a conventional feed tag, which is precisely the point the authors emphasise. Poor nutritional management rooted in poor-quality feeds is identified as the primary on-farm constraint limiting milk yield on smallholder tropical dairy farms, frequently pushing animals into negative energy and protein balance. By publishing a consistent, regionally grounded CNCPS reference dataset for thirteen ingredients analysed in a single run, the Kerala team has given South Asian nutritionists the raw material to formulate diets around ruminal degradation kinetics rather than proximate composition alone. The researchers frame the work as a starting point: wider sampling across different agro-climatic zones and supply chains will be needed to expand it into a comprehensive regional feed library, and future studies should progressively adopt the updated CNCPS v6.5 fractionation framework, with careful attention to how the older fraction definitions map onto the newer pool structure.

Subject of Research: CNCPS-based carbohydrate and protein fractionation of tropical ruminant concentrate feed ingredients for precision diet formulation

Article Title: CNCPS-based carbohydrate and protein fractionation of feed ingredients commonly used in tropical ruminant diet formulation

Article References: Sahib, L., Kulangara, A., Kalarikkal Subramanian, A., Chacko, B., Gopalakrishnan, R., & Kundukulam Sunny, A. (2026). CNCPS-based carbohydrate and protein fractionation of feed ingredients commonly used in tropical ruminant diet formulation. Discover Animals, 3(1), Article 100. https://doi.org/10.1007/s44338-026-00245-4

Image Credits: AI Generated

DOI: 10.1007/s44338-026-00245-4

Keywords: CNCPS, feed fractionation, tropical ruminants, rumen degradability, concentrate ingredients, South Asia, precision feeding, dairy nutrition, protein fractions, carbohydrate fractions, RDP RUP, livestock