Lysine occupies a special place in poultry nutrition. In conventional corn–soybean meal diets it is typically the second most limiting essential amino acid, and it serves as the reference point around which the entire ‘ideal protein’ concept is built. Once lysine is supplied at the correct level, all other essential amino acids can be balanced against it in fixed ratios, allowing nutritionists to formulate diets that match physiological needs while minimising costly and environmentally damaging nitrogen excretion. But lysine does far more than simply build protein. It is a precursor for carnitine, which shuttles fatty acids into mitochondria for energy production, and it helps activate the mTOR signalling pathway that governs the rate of protein synthesis in growing tissues. Deficiency stunts growth and weakens immunity; oversupply disrupts amino acid balance and forces the body to pay a metabolic penalty for degrading the excess.

Despite this central role, estimates of lysine requirements for starter-phase Japanese quail have varied widely in the literature, generally falling between 1.20% and 1.40% of the diet. Part of the discrepancy reflects methodological differences, part reflects genetic progress: modern quail strains bred for faster growth and better feed efficiency may simply need more than the standards set decades ago. To resolve the question, researchers at the University of Tabriz in Iran conducted one of the most comprehensive requirement studies to date, raising 900 day-old quail chicks across 15 different dietary treatments in a carefully controlled 3 × 5 factorial design.

The experimental architecture was deliberately thorough. Three crude protein levels—22%, 24% and 26%—were crossed with five lysine levels ranging from 0.95% to 1.55% of the diet. Chicks were housed in 90 floor pens with six replicate pens per treatment, under a 23-hour light photoperiod with ambient temperature stepping down from 35°C to 29°C over the two-week trial. Crucially, all other essential amino acids were held in fixed ratios to lysine according to the ideal protein concept, with crystalline amino acids used to guarantee that methionine, threonine, tryptophan, arginine, leucine, isoleucine and the sulphur amino acids never became limiting. Diets were verified analytically by high-performance liquid chromatography, confirming that what was formulated was what the birds actually ate.

The growth results told a clear story. Body weight and weight gain rose as dietary protein increased, with chicks on 26% crude protein reaching a final body weight of 71.72 grams compared with roughly 69.3 grams at the lower protein levels. Feed intake, intriguingly, moved in the opposite direction, declining as protein density rose—a pattern the authors attribute to improved amino acid balance and metabolic efficiency reducing the drive to overeat. Lysine produced a classic quadratic response: performance climbed steadily up to 1.4% dietary lysine, where chicks achieved their peak body weight of 73.93 grams and weight gain of 66.50 grams, then declined at 1.55%, signalling that beyond a physiological threshold, extra lysine becomes a liability rather than an asset.

Perhaps the most consequential finding was the significant interaction between protein level and lysine for feed intake, feed conversion ratio and protein efficiency ratio. At 22% crude protein, performance kept improving as lysine rose to 1.4%, indicating that birds on reduced-protein diets depend heavily on supplemental lysine to compensate for the lower total amino acid supply. At 24% and 26% protein, the response flattened out much earlier, with little benefit beyond 1.25% lysine, because intact protein sources were already delivering ample lysine on their own. This context-dependence helps explain why lysine requirement estimates have bounced around the literature for years: studies using different basal protein levels were, in effect, measuring different things.

Carcass data reinforced the message that balance beats brute force. Carcass yield and breast muscle yield peaked at 24% crude protein and declined at 26%, suggesting that very high protein intake carries metabolic costs—extra heat production and increased liver workload from nitrogen deamination—that erode the efficiency of protein deposition. Breast muscle proved especially sensitive to lysine, climbing from 29.6% of live weight at 0.95% lysine to 32.0% at 1.25% before plateauing. Because breast meat yield is a key economic driver in meat-type quail production, this sensitivity matters commercially. A significant protein × lysine interaction for breast yield confirmed that the optimal lysine level for muscle development shifts with the surrounding dietary protein context.

The statistical side of the study carries lessons of its own. The researchers fitted both linear and quadratic broken-line regression models, which locate the ‘breakpoint’ at which the response to a nutrient plateaus. Across nearly all response criteria, the linear model outperformed the quadratic version, delivering higher coefficients of determination and tighter confidence intervals. The quadratic model consistently produced requirement estimates 0.04 to 0.07 percentage points higher, likely reflecting overfitting of the pronounced peaks in the data. Using linear broken-line analysis, the lysine requirement for weight gain was estimated at 1.20% of diet at 22% crude protein, 1.32% at 24%, and 1.40% at 26%—values that generally exceed older recommendations but align with recent factorial modelling of modern quail strains, including a 2023 estimate of roughly 1.35% to 1.45% of diet for growing quail.

Mechanistically, the response patterns map neatly onto established biochemistry. Suboptimal lysine intake dampens mTOR activation, slowing translational efficiency and cell growth, which explains the steep performance gains as lysine approaches the requirement. Beyond the breakpoint, surplus lysine must be deaminated and converted to urea, processes that generate metabolic heat and burden the liver and kidneys—a penalty visible in the reduced protein efficiency ratio observed at 1.55% lysine. The study’s authors are careful to note limitations: the trial used optimal environmental conditions that may not reflect commercial farms, covered only the 0–14 day starter phase, and did not include economic analysis of supplementation decisions.

The practical take-home for producers is a set of context-specific targets rather than a single magic number. For diets containing 22% or 26% crude protein, the study supports lysine levels of 1.40% to 1.42%, while 1.32% to 1.35% suffices at 24% crude protein. These figures prioritise both growth and feed efficiency while limiting nitrogen excretion, a growing regulatory and environmental concern for poultry operations worldwide. The authors call for follow-up work on later growth phases, dynamic requirement models that track changing needs along the growth curve, interactions with alternative protein ingredients, and the influence of heat stress on lysine metabolism. For now, the message is clear: as quail genetics have sprinted ahead, feeding standards have lagged behind, and precision nutrition—right amino acid, right protein context, right statistical model—is the way to catch up.

Subject of Research: Lysine requirement estimation for starter-phase Japanese quail using dose–response modelling across dietary protein levels

Article Title: Lysine Requirements in Starter‐Phase Japanese Quail (Coturnix japonica) Through Dose–Response Modelling: Interactions With Dietary Protein Level

Article References: Valizadeh, H., Taghinejad‐Roudbaneh, M., & Kianfar, R. (2026). Lysine Requirements in Starter‐Phase Japanese Quail ( Coturnix japonica ) Through Dose–Response Modelling: Interactions With Dietary Protein Level. Veterinary Medicine and Science, 12(6), Article e71142. https://doi.org/10.1002/vms3.71142

Image Credits: AI Generated

DOI: 10.1002/vms3.71142

Keywords: Japanese quail, lysine, poultry nutrition, dose–response modelling, broken-line regression, ideal protein, crude protein, feed conversion ratio, breast muscle yield, starter phase, amino acid requirements, precision feeding

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