Ask ten producers what a balanced poultry diet is and you get ten nutrient lists. Protein, energy, calcium, vitamins. All correct, none of it decisive. The question that separates a flock holding its growth curve from one drifting off it is narrower than that: which specification are you formulating against, and does the bird eat enough of it for the specification to mean anything?
Key takeaways
- Crude protein is a weak target. Digestible lysine, with the other amino acids expressed as a ratio to it, is what a formulation actually runs on.
- Breeder specifications get revised. Aviagen’s digestible lysine figure for Ross starter feed reads 1.28% in its 2014 specification and 1.32% in the 2022 one.
- For layers, limestone particle size changes how much calcium a hen has to eat to reach the same shell quality.
- What may legally enter the ration is regional. Since 6 September 2021 the EU permits porcine and insect processed animal protein in poultry feed, while ruminant meat-and-bone meal stays prohibited.
Crude protein is the number people argue about, and the wrong one
Formulation for growing birds runs on digestible amino acids, not on crude protein. Crude protein is a nitrogen measurement. It says nothing about whether lysine, methionine and threonine arrive in usable proportions, or whether the bird can absorb them once they do. Two rations at the same protein percentage can perform very differently, and the amino acid profile behind the headline figure explains why.
The convention that replaced it is straightforward. Set digestible lysine first, then express every other essential amino acid as a percentage of lysine, the approach usually called ideal protein. Lysine serves as the anchor because it is measured reliably and its requirement scales cleanly with lean tissue growth.
What matters operationally is that the anchor itself moves. Aviagen’s Ross broiler nutrition specifications for a 1.70 to 2.40 kg target liveweight listed digestible lysine at 1.28% in starter, 1.15% in grower and 1.03% in finisher in the 2014 document. The 2022 specification, built around a four-phase program, lists 1.32%, 1.18%, 1.08% and 1.02%. The direction is upward at the front of the cycle, which is where the modern bird lays down most of its frame.
| Phase | Ross 2014 spec, digestible lysine | Ross 2022 spec, digestible lysine |
|---|---|---|
| Starter | 1.28% | 1.32% |
| Grower | 1.15% | 1.18% |
| Finisher (finisher 1 in 2022) | 1.03% | 1.08% |
| Finisher 2 | not in this program | 1.02% |
Read that as a direction of travel rather than a like-for-like comparison: the two documents describe different phase programs and different weight targets. The point stands anyway. A spec sheet printed once and taped to the mill wall stops being a specification and becomes a habit.
Energy sets intake, so energy sets everything else
Birds eat largely to meet an energy requirement, which means the energy density of the feed decides how many grams go down the throat each day. Raise the energy level and daily intake falls. Every other nutrient supplied per bird per day falls with it, whether or not anyone changed those lines in the formula.
That is the reason amino acids are specified relative to energy rather than as free-standing percentages. Adjust the fat inclusion to take advantage of an oil price and you have quietly changed the effective lysine intake of the flock. The formula still looks compliant. The bird is not receiving what the formula says.
For layers, calcium is a particle size question before it is a percentage
The calcium figure on a layer feed label describes the quantity, not the delivery. Work summarized in the poultry nutrition literature found that hens taking in 2 g of calcium a day from large limestone particles reached an average eggshell specific gravity of 1.080, while hens on very fine limestone had to eat 3 g a day to reach the same standard. Same mineral, same target, a third more consumption to get there.
The mechanism is mechanical. Coarse particles are retained in the gizzard and dissolve slowly, which keeps calcium available through the night, when shell calcification actually happens. Fine limestone passes through and is largely gone by the time the hen needs it. Published work points to roughly 1 mm as the minimum particle size for meaningful selective retention in the gizzard of commercial white layers, with medium grades in the 2 to 5 mm range commonly recommended for performance and bone quality.
Fiber behaves in a related way, influencing gizzard function and retention time rather than supplying a nutrient directly, which is why we treat it as a structural decision rather than a filler. That argument is set out separately in our piece on the role of fiber in a laying hen’s diet.
What may legally enter the ration depends on where the mill stands
Ingredient advice does not travel across borders, and animal proteins are the clearest case. In the European Union, Commission Regulation (EU) 2021/1372, applicable from 6 September 2021, re-authorized processed animal protein of porcine origin in poultry feed, along with insect protein, under strict conditions on collection, dedicated processing lines and routine sampling to exclude cross-contamination with ruminant material. Ruminant meat-and-bone meal remains banned, and the intra-species recycling prohibition still stands, so poultry protein does not go back into poultry feed. A ration sheet written where meat-and-bone meal is unrestricted is therefore not portable, and each animal-derived ingredient needs checking against the rules of the jurisdiction where the feed is manufactured.
The specification only counts if it reaches the crop
A formulation is a statement of intent. What the flock receives is a physical product with a form, a fines fraction and a distribution along the feeder line. Birds select against fines when they can, so a pellet that arrives substantially broken down is no longer the ration that was formulated, whatever the delivery note says. Feed intake also follows water intake closely, and a restricted or warm drinker line suppresses consumption before anything is visible in the feed itself.
Four checks worth running on your own specification
- Date the spec sheet. Identify which breeder revision you are formulating against, and for which target liveweight and phase program. A 2014 document and a 2022 document are not the same brief.
- Read amino acids as ratios to digestible lysine, then check those ratios against the energy level you actually run, not the one the specification assumes.
- Ask your limestone supplier for a particle size distribution, not just a calcium assay. On layer feed this is the cheapest shell quality intervention available.
- Sample at the feeder, not at the bin. Check pellet integrity and fines where the birds eat, against what left the mill.
Questions that come up when we walk through this
Is a higher protein feed always better for growth?
No. Beyond the point where the limiting amino acid is satisfied, additional nitrogen is deaminated and excreted rather than converted into tissue. It costs money in the formula, and it raises litter moisture and ammonia load in the house. The balance between amino acids does more for growth than the height of the protein figure.
Are the NRC tables still a valid formulation target?
They are a reference framework, not a target for modern commercial strains. The National Research Council’s Nutrient Requirements of Poultry is still in its ninth revised edition, published in 1994, and a tenth revised edition has been in preparation through the National Academies. Genetic progress since then has been substantial, which is why breeder specifications, revised on a much shorter cycle, do the day-to-day work.
Who should sign off a feed change on a flock with a health problem?
The flock veterinarian, together with the nutritionist. Feed is a tempting lever because it is under your control, but a ration change made to treat a suspected disease can mask the clinical picture and delay diagnosis. Nutrition supports the immune response; it does not substitute for a veterinary assessment.
From specification to feed pan
Getting the numbers right is half the job. The other half is what happens between the mill and the bird, which is where most of the loss occurs.
Sources: Aviagen, Ross Broiler Nutrition Specifications 2014 and 2022; peer-reviewed work on limestone particle size, eggshell quality and gizzard retention in laying hens; Commission Regulation (EU) 2021/1372; National Research Council, Nutrient Requirements of Poultry, ninth revised edition, 1994, and the Nutrient Requirements of Poultry 10th Revised Edition project at the National Academies. Consulted August 2026.
This article covers nutrition and feed management. Diagnosis and treatment of flock health problems are veterinary decisions and fall outside its scope.