Reduced-protein layer diets improved digestibility, with enzyme caveats

CURRENT FULL VERSION: A June 3, 2026, study in Animals takes a closer look at a question poultry nutritionists have been circling for years: can enzyme packages make reduced-protein layer diets work better, without giving up production? In this trial, researchers found that reduced-protein diets did improve nutrient utilization and lowered protein excretion in laying hens, but the performance picture was mixed. Egg weight fell across the study, egg mass dipped early, and the higher inclusion rate of xylanase plus β-glucanase reduced hen-day egg production in the later phase. (researchgate.net)

The study comes at a time when reduced-protein feeding is attracting more attention because soybean meal costs, sustainability pressures, and nitrogen management are all pushing producers to get more from each unit of dietary protein. The authors note that reduced-protein diets are appealing because they can lower feed cost and nitrogen excretion, but also warn that amino acid supplementation alone may not solve digestibility limits tied to phytate and non-starch polysaccharides. That’s the rationale for adding enzymes such as phytase, xylanase, and β-glucanase, though published responses have been inconsistent. A useful parallel comes from outside poultry: a recent Veterinary Sciences trial in 200 weaned piglets found that reducing crude protein by 2% lowered body weight and average daily gain across a 31-day period, and adding protease at 0.1 g/kg only partially restored those losses. Notably, that piglet study did not find significant changes in dry matter, nitrogen, or energy digestibility, feed conversion, or fecal score, underscoring a broader point that enzyme supplementation does not always translate into a full performance rescue when protein is cut too far. (researchgate.net)

In the new work, 208 hens were assigned to eight treatments in a 2 × 2 × 2 factorial design from 35 to 57 weeks of age. The diets compared standard protein at 16.5% crude protein versus reduced protein at 14.5%, phytase at 600 or 1200 FTU/kg, and xylanase/β-glucanase at 100 or 150 g/ton. Across the full period, there were no significant interactions for overall laying performance, but the reduced-protein diets consistently lowered egg weight. They also reduced yolk weight at 47 weeks, and by 57 weeks they decreased albumen weight and albumen proportion while increasing yolk proportion. Meanwhile, the higher carbohydrase dose, 150 g/ton, lowered hen-day egg production during weeks 48 to 57 and reduced shell breaking strength at 57 weeks. (researchgate.net)

The clearest upside was on nutrient use and waste output. Reduced-protein diets lowered excreta moisture, improved dry matter digestibility, increased apparent metabolisable energy digestibility, increased apparent protein digestibility, and sharply decreased protein excretion. The authors concluded that reducing protein to an appropriate level may offer environmental benefits without hurting feed efficiency. That conclusion fits with broader recent literature showing that lower-protein layer diets can reduce nitrogen and ammonia burdens, but only if amino acid balance and enzyme strategy are tight enough to avoid hidden performance losses. The piglet protease study adds a useful caution here as well: even when lower-protein programs are nutritionally intentional, maintaining growth or production is not guaranteed, and enzyme support may only partly compensate rather than fully normalize outcomes. (researchgate.net)

The mixed enzyme response is probably the most practical takeaway. Other recent layer studies have shown that xylanase or enzyme blends can improve egg production, egg mass, shell quality, gut integrity, or nutrient digestibility in nutrient-reduced diets, but they’ve also emphasized that results vary by substrate, dose, and bird age. One 2025 Animals study reported better egg production, egg mass, and shell quality with 50 to 100 g/MT xylanase in energy-reduced diets, while noting poorer outcomes at the highest dose tested. A 2024 study also found phytase and xylanase could improve phosphorus use and some performance measures in layers. In that context, the new study’s signal is less that enzymes failed, and more that inclusion rate matters, especially in reduced-protein, post-peak flocks. The same principle appears in swine nutrition: in the weaned piglet protease trial, a 1% crude-protein reduction was tolerated better than a 2% cut, and protease improved performance only partially, reinforcing that the margin for safe protein reduction can be narrow. (mdpi.com)

For veterinary professionals working with commercial poultry systems, this is a formulation and flock-management story as much as a nutrition story. Lower protein excretion can translate into less nitrogen loading and potentially better house conditions, including litter and ammonia management, which can affect respiratory health, welfare, and egg cleanliness. But the downside risk is also familiar: if the protein cut is too aggressive, or if the enzyme matrix overpromises, the losses may show up first in egg size, shell quality, or late-cycle production rather than in feed conversion alone. That makes veterinary oversight important when nutrition changes intersect with shell defects, flock persistence, and environmental control. The cross-species pattern from piglets strengthens that practical message: performance can slip even when digestibility or manure-related measures look acceptable on paper. (researchgate.net)

There doesn’t appear to be a separate company press release or major industry statement attached to this paper, and publicly visible commentary so far is limited. Still, the study is likely to be read as a caution against assuming that higher enzyme inclusion automatically delivers better biological returns. The broader industry direction remains clear: reduced-protein feeding is still attractive, but precision matters more than ever, especially as producers try to balance ingredient economics, sustainability targets, and egg output in older hens. Findings from other species, including the recent piglet protease work, point in the same direction: lower-protein programs may be feasible, but the biological tradeoffs remain highly dose- and context-dependent. (researchgate.net)

Why it matters: This paper gives veterinary teams and poultry nutrition advisers a more nuanced benchmark for reduced-protein programs in layers. It supports the environmental case for protein reduction, particularly around protein excretion, but it also suggests that post-peak hens may not fully tolerate every enzyme-rate combination without tradeoffs in egg size or shell metrics. In practice, that means ration changes should be interpreted alongside production records, shell quality trends, and housing conditions, not just digestibility data. The broader feed-management lesson, echoed by recent piglet data, is that enzymes may help at the margins but may not fully reverse the consequences of a deeper protein cut. (researchgate.net)

What to watch: Expect follow-up work to focus on commercial validation, narrower enzyme dose optimization, and whether different grain bases or amino acid strategies can preserve the digestibility and nitrogen benefits while protecting egg weight and shell strength in later-lay hens. A related question across species is where the practical lower limit for crude-protein reduction really sits before performance losses become too costly, even with enzyme support. (researchgate.net)