A study published in December 2026 in Poultry Science, Volume 105, Issue 12, examines how three dietary levers — net energy, crude protein, and standardized ileal digestible lysine — affect growth performance, nitrogen utilization, and hepatic metabolism in broilers between 22 and 35 days of age. The window matters commercially: it is the grow-out phase in which feed conversion and nitrogen excretion are largely determined, and in which most flock-level feed-cost decisions are locked in.

Who ran the study, and how it is structured

The author team — Yao Yu, Caiwei Luo, Tahir Mahmood, Li Chen, Yves Mercier, and Jianmin Yuan — reports in Poultry Science, the flagship journal of the Poultry Science Association. The paper's title identifies the three dietary factors under test and the three outcome domains measured: growth performance, nitrogen utilization, and hepatic metabolism. That combination of outcomes is the study's distinguishing feature. Feeding trials in broilers routinely measure growth and feed conversion. Fewer pair those with nitrogen-balance data and liver-metabolism readouts in the same experiment, and the linkage is what gives the work its practical weight.

Why these three nutrients together?

Net energy, crude protein, and standardized ileal digestible lysine interact. Net energy describes the energy actually available to the bird after digestive and metabolic losses. Crude protein sets the total nitrogen load entering the bird, digestible or not. Standardized ileal digestible lysine corrects for what the bird actually absorbs at the terminal ileum — the metric most feed formulators now use as the reference amino acid against which all others are ratioed. Adjusting one without the other two can mislead: protein can appear adequate on paper while delivering surplus nitrogen the bird excretes, or energy density can mask an amino acid shortfall.

For the study cohort, the 22-to-35-day span covers the finisher phase, when feed intake per bird peaks and when the gap between formulated and delivered nutrition shows up most clearly in flock uniformity and litter nitrogen.

What the outcome domains signal for practice

Each of the three measured domains maps to a distinct decision point at the farm level.

• Growth performance — weight gain and feed conversion in this phase determine closeout economics. Phase-specific dietary energy and lysine settings are the formulator's main remaining cost levers once genetics are fixed.
• Nitrogen utilization — retention versus excretion drives both feed-protein efficiency and environmental loading. Litter nitrogen is an increasing regulatory and neighbor-relations issue in dense poultry regions, making retention data a compliance input as much as a nutrition input.
• Hepatic metabolism — the liver is the site of deamination and urea-cycle-adjacent processing in birds; changes here indicate the metabolic cost the bird pays to handle dietary nitrogen surpluses. These readouts can reveal whether performance holds only by shifting metabolic burden to the liver.

The value of measuring all three in one design is coherence. A diet that sustains growth while improving nitrogen retention and leaving hepatic markers undisturbed is a different proposition from one that holds weight gain only by pushing nitrogen-handling load onto the liver.

Why the reader should note the framing

This report concerns a study's publication — its authorship, its placement, and the variables and outcomes its title declares. The full text in Poultry Science, Volume 105, Issue 12, carries the experimental design details, dietary specifications, and quantitative results, and readers making formulation decisions should consult those tables directly. The December 2026 publication places the findings in the current literature stream on precision protein feeding, where reducing crude protein while holding digestible amino acid ratios is an active strategy for cutting excretion without sacrificing gain.

With feed the dominant cost of broiler production and nitrogen output an environmental pressure point, studies that quantify the trade space among energy, protein, and digestible lysine in the finisher phase — as this Poultry Science paper sets out to do — will inform how phase-feeding programs are tuned in the seasons ahead.

By Amara Osei, The Vet Scope