Phytase in Animal Feed: Phytate, FTU Units, Matrix Values and Superdosing

Phytase is a feed enzyme that releases phosphorus from phytate in plant ingredients, and the EU sets its legal minimum content for chickens for fattening product by product, from 125 FTU/kg (4a27) to 500 FTU/kg (4a37) of complete feed (12 % moisture). Each authorisation fixes its own animal categories, unit and end date.

Phytase belongs to category 4, zootechnical additives, one of the five types of feed additives in Regulation (EC) No 1831/2003. In the US it has no 21 CFR section. The key facts follow.

• EU functional group 4a, digestibility enhancers, like the other feed enzymes.
• EU legal minimum content only: no EU maximum content and no withdrawal period is set.
• FTU, FYT, OTU, PPU and U are never converted 1:1.
• US: animal-food GRAS notices with FDA "no questions" letters, not approvals.

What Is Phytase?#

Phytase is a phosphatase enzyme that removes phosphate groups step by step from phytate (myo-inositol hexakisphosphate, InsP6), and the EU authorises it as a zootechnical feed additive in functional group 4a digestibility enhancers. Two enzyme types are used: 3-phytase (EC 3.1.3.8) and 6-phytase (EC 3.1.3.26).

The producing organisms are mostly genetically modified strains of Trichoderma reesei, Aspergillus, Komagataella and Schizosaccharomyces pombe, which is why feed phytase is called microbial phytase. The annexes treat the product as a respiratory sensitiser; for the hazard line see the product SDS.

Phytate, the substrate phytase breaks down#

Phytate holds phosphorus that pigs and poultry digest poorly, and it also binds calcium, zinc, amino acids and energy in the gut. That anti-nutritional effect is why phytase reduces inorganic phosphate supplementation and phosphorus excretion.

Phytate also binds zinc in the digesta; the feed side of that binding is covered under zinc in animal feed. One EU fish entry (4a16) applies to feed containing more than 0.23 % phytin-bound phosphorus, an example of phytate level written into an act.

How Does Phytase Work in Poultry and Pigs?#

Phytase works in the upper digestive tract, the crop, proventriculus and gizzard of poultry and the stomach and upper small intestine of pigs, where phytate is soluble. It dephosphorylates InsP6 stepwise into lower inositol phosphates and inositol, which releases phosphorus and calcium and reduces phytate-protein and phytate-mineral complexes. Added activity was not recovered in the pig ileum (Dersjant-Li et al., 2015, Journal of the Science of Food and Agriculture 95:878).

3-phytase and 6-phytase: where dephosphorylation starts#

3-phytase starts removing phosphate at the 3-position of the phytate ring and 6-phytase at the 6-position, and the IUBMB accepted name of 6-phytase is 4-phytase because the name "6-phytase" follows 1L-numbering. The two types differ as follows.

• Start position: 3-phytase at the 3-position; 6-phytase at the 6-position (4-position in D-numbering).
• EC number: 3-phytase EC 3.1.3.8; 6-phytase EC 3.1.3.26.
• Origin: fungal Aspergillus niger enzymes for the 3-phytases; E. coli-type (appA), Buttiauxella and Citrobacter-type histidine acid phosphatases for the bacterial 6-phytases.
• pH and pepsin profile: fungal A. niger 3-phytases show a lower pH optimum spread and lower pepsin resistance; the bacterial 6-phytases have pH optima of about 2.5 to 5.5 and good pepsin resistance.

These are profiles, not a ranking.

Phytase Units: FTU, FYT, OTU, PPU and U#

Five activity units are in use in EU phytase acts, and each is defined as 1 µmol of inorganic phosphate liberated per minute under its own assay conditions. One FTU is that amount from sodium phytate at pH 5.5 and 37 °C, the definition used in annexes such as Implementing Regulation (EU) 2020/172.

The table compares the four units whose definitions the acts give; entries marked U define the unit in each act, so no definition is written here.

Phytase activity units (implementing regulations, read 2026-11-03)

Units are never converted 1:1, because 1 FTU of product A is not 1 FTU of product B in vivo: intrinsic efficacy differs between enzymes.

Measuring phytase activity in feed: EN ISO 30024 and AOAC 2000.12#

EN ISO 30024 is a colorimetric phosphomolybdate method that cannot distinguish added phytase from intrinsic plant phytase. The 2009 first edition is superseded in scope by the 2024 second edition, which extends it to plant raw materials and compound feeds.

AOAC 2000.12 (Engelen et al., 2001, Journal of AOAC International 84:629) was validated at 200 to 400 FTU/kg across 14 and 13 laboratories, with repeatability RSDr of 2.5 to 8.6 % and reproducibility RSDR of 14 to 27.6 %. With reproducibility that wide, one feed assay is not proof of under-supply.

Which Phytases Does the EU Register List?#

The EU Register lists 3-phytases and 6-phytases from several holders, each authorised by its own implementing regulation for named animal categories at a legal minimum content in the holder's own activity unit. The tables below follow the implementing regulations and the register as read on 3 November 2026; they show the entries recorded for this page, not the whole register.

3-phytase entries: 4a1600, 4a25 and 4a50#

BASF SE holds 4a1600 and Fertinagro holds 4a25 and 4a50, with legal minimum contents from 100 FTU/kg (pigs for fattening, 4a1600) to 1 000 FTU/kg (laying hens, 4a25 and 4a50).

EU 3-phytase entries (implementing regulations and EU Register, read 2026-11-03). 3-phytase: EC 3.1.3.8, CAS 37288-11-2

Legal minimum content per kg complete feed at 12 % moisture, in the unit of each act; not a recommended inclusion. No maximum content and no withdrawal period are set. Units are not interchangeable.

The EU Register also lists the 2017/895 entry for 4a25 in Annex 2 (end date 2027-06-14); the table shows the later acts. A further 3-phytase from Trichoderma reesei CBS 528.94 (turkeys for fattening and sows) was withdrawn by Implementing Regulation (EU) 2025/2575 with transitional measures.

6-phytase (4-phytase) entries from 4a1640 to 4a64#

Most EU entries are 6-phytases from Trichoderma reesei, Aspergillus, Komagataella or Schizosaccharomyces strains, authorised in FTU, FYT, OTU, PPU or U, and the table lists them in ID order because the units differ and ascending order would imply comparability.

EU 6-phytase entries (implementing regulations and EU Register, read 2026-11-03). 6-phytase (IUBMB accepted name 4-phytase): EC 3.1.3.26, CAS 9001-89-2

Legal minimum content per kg complete feed at 12 % moisture, in the unit of each act; not a recommended inclusion. No maximum content and no withdrawal period are set. Units are not interchangeable.

The 4a27 minimum for chickens for fattening and reared for laying is 125 FTU/kg since Implementing Regulation (EU) 2019/1290 of 31 July 2019, which reduced the 750 FTU/kg of the original Implementing Regulation (EU) 2018/338. The 4a19 entry now rests on Implementing Regulation (EU) 2026/91, which repeals Regulation (EU) No 292/2014, with transitional measures to 4 February 2027.

Two entries carry a past printed expiry: 4a23 (29 March 2026) and 4a24 liquid (29 June 2026). For both, the EU Register records a renewal application and still lists the entry pending the Commission decision (Article 14 of Regulation (EC) No 1831/2003).

What Does the Evidence Show for Phytase?#

Meta-analyses show that phytase raises phosphorus digestibility in pigs and restores eggshell quality and egg production in phosphorus-deficient hen and breeder diets, and the size of the effect depends on dietary calcium and phytate. Selle and Ravindran (2007, Animal Feed Science and Technology 135:1-41) is the benchmark review of microbial phytase in poultry.

Meta-analyses in pigs, broiler breeders and laying hens#

Velayudhan, Marchal and Dersjant-Li (2019, Journal of Animal Science 97, Suppl 3) pooled 19 studies with 766 data points and found that Buttiauxella phytase at 250 to 2 000 FTU/kg raised apparent total tract digestibility (ATTD) of phosphorus in pigs exponentially. The laying-hen result bears on eggshell quality, where Lima et al. (2026) measured gains in shell thickness and breaking strength.

The table compares four reviews and two single trials; no broiler meta-analysis with a verified effect size is recorded, and all effects are against phosphorus-deficient controls.

Phytase evidence (named studies)

Why phytase responses vary: calcium, limestone and phytate level#

Phytase responses vary with dietary calcium, the calcium to phosphorus ratio, limestone particle size and phytate content. High calcium, a wide Ca:P ratio and coarse limestone reduce phytase efficacy.

The pig meta-analysis found negative correlations with all three, and the breeder meta-analysis found a larger gain when phytate phosphorus reached 2.5 g/kg and calcium was below requirement. A response measured with one product at a given FTU level does not transfer to another.

Phytase Matrix Values: How Released Nutrients Are Credited#

A phytase matrix value is the amount of digestible phosphorus, calcium and other nutrients a nutritionist credits to a given phytase activity in the formula, so that feed phosphate and other sources can be reduced. The credit is set per product and species, and a matrix is not carried across products by FTU number.

Which nutrients a phytase matrix covers and how it is set#

A phytase matrix covers up to five nutrient groups, listed below, and it is selected together with intrinsic efficacy, thermostability, form and register coverage per species.

• Available or STTD phosphorus (avP, standardised total tract digestible P).
• Calcium.
• Sodium.
• Digestible amino acids.
• Metabolisable energy (ME).

One product-specific example from a named trial: in grow-finish pigs, Holloway et al. (2018, Iowa State) used a Quantum Blue (AB Enzymes Finland Oy, 4a19) inclusion of 0.005 % of the diet, which supplied at least 250 FTU/kg and was assumed to release 0.08 % STTD phosphorus.

At superdosing levels the matrix is not extended: the extra-phosphoric benefit of a superdose is taken as performance, not as matrix credit.

Phytase Superdosing: 1 500 to 2 500 FTU/kg in Trials#

Phytase superdosing means feeding activity well above the level used to replace feed phosphate, usually 1 500 to 2 500 FTU/kg in trials, to destroy phytate almost completely and gain extra-phosphoric effects. These are trial and practice levels, not legal values, and the responses include the feed conversion ratio.

In one broiler trial (Kiarie, Woyengo and Nyachoti, 2015), 2 000 FTU/kg of Buttiauxella phytase on a diet with 40 % less available phosphorus and 17 % less calcium raised body weight gain by 20 % and improved FCR by 7.4 % against the negative control, from a single trial that is not a general effect.

A second single trial (de Léo et al., 2026, British Poultry Science) tested broilers on corn-soy-meat and bone meal diets and found that 2 000 and 2 500 FTU/kg gave the best gain, FCR and the highest tibia calcium and phosphorus.

How Much Phytase Goes into Feed?#

Feed must contain at least the EU legal minimum of the product used, from 100 FTU/kg for pigs for fattening (4a1600, 4a27) to 2 500 FTU/kg for other fin fish (4a19), and no maximum content or withdrawal period is set.

EU legal minimum content by animal category#

The EU legal minimum content is the lowest activity per kg complete feed (12 % moisture) that the act requires for the named animal category when the additive is used. The table gives the lowest and highest FTU value per category and lists other units separately.

EU legal minimum content by animal category (implementing regulations, read 2026-11-03)

The minimum is read as follows.

• It is the least activity the feed must contain, in the act's unit.
• It is not a recommended inclusion, an optimum or a maximum; the 2 000 FTU/kg of 4a24 (Implementing Regulation (EU) 2017/896) and 1 000 FTU/kg of 4a25 (Implementing Regulation (EU) 2017/895) are other provisions, not legal maxima.
• It cannot be moved to another unit or another product.

Pelleting, post-pellet liquid application and premix storage#

Pelleting heat reduces phytase activity, so coated granulates go into the mash and liquids are sprayed after pelleting. In a pelleting study, raising conditioning from 74 to 85 °C lifted the hot pellet temperature from 80.1 to 87.5 °C and the pellet durability index from 84.3 to 88.2 %, and phytase stability decreased linearly (Truelock et al., 2020, Journal of Animal Science).

Premix storage adds a second loss route. In a premix storage study (Translational Animal Science, doi 10.1093/tas/txaa049), phytase was stable at 22 °C and 28.4 % relative humidity, fell dramatically at 39.5 °C and 78.8 % humidity and lost 20 % after a 60 °C heat pulse of about 9.5 hours, which is why activity is checked in feed premixes as well as in finished feed.

The acts require the directions for use to state storage conditions and stability to heat treatment. Forms differ: coated thermostable granulate at 5 000 to 65 000 FTU/g, powder up to 100 000 FTU/g, and liquid for post-pellet application at 5 000 to 20 000 FTU/g or mL.

Phytase for Poultry, Pigs and Fish#

EU phytase authorisations name animal categories exactly, so a product authorised for chickens for fattening reaches laying hens only where its act names laying birds. The table maps categories to example entries and species pages.

Animal categories, example entries and species pages

Phytase in poultry feed: broilers, laying hens and turkeys#

Phytase entries for chickens for fattening carry legal minimum contents of 125 to 500 FTU/kg, and entries for laying hens 150 to 1 000 FTU/kg, depending on the product. Examples are 4a27 at 125 FTU/kg and 4a37 at 500 FTU/kg for chickens, and 4a1640 and 4a19 at 150 FTU/kg and 4a25 and 4a50 at 1 000 FTU/kg for laying hens.

For turkeys for fattening, 4a1600 sets 250 FTU/kg, 4a27 125 FTU/kg and 4a37 500 FTU/kg. 4a1600 sets 300 FTU/kg for ducks.

Phytase in pig feed: piglets, finishers and sows#

Pig phytase entries differ by category, as 4a1600 shows with 500 FTU/kg for piglets and sows and 100 FTU/kg for pigs for fattening. For weaned piglets the legal minimum runs from 125 to 1 000 FTU or U per kg depending on the product, with 4a27 at 125 FTU/kg and 4a31 at 1 000 U/kg. Sows reach 500 FTU/kg (4a1640, 4a37).

Phytase in fish feed#

Phytase entries for fish include 4a19, 4a48 and 4a16, with legal minimum contents of 500 to 2 500 FTU/kg (4a19), 1 000 FYT/kg (4a48) and 500 OTU/kg (4a16, for feed with more than 0.23 % phytin-bound phosphorus).

EU and US Status of Phytase Side by Side#

In the EU each phytase needs a holder-bound implementing regulation that fixes animal categories and a legal minimum, while in the US no phytase has a 21 CFR section and market access runs through animal-food GRAS notices and the AAFCO Official Publication. The table compares the two systems.

EU and US status of phytase (read 2026-11-03)

EU: holder-bound 4a authorisations and printed expiries#

Each EU phytase authorisation names a holder, a production strain, animal categories, a legal minimum and an end date, runs for ten years and can be renewed under Article 14. Holders change by act: Implementing Regulation (EU) 2026/180 moved 4a18i and 4a48 to Novozymes A/S, and Implementing Regulation (EU) 2025/316 moved 4a19 to AB Enzymes Finland Oy.

EFSA concluded for 4a1600 (EFSA Journal 2019;17(3):5640) and the 4a19 renewal (EFSA Journal 2025;23:e9463) that consumers face no concern and need no MRL or ADI, that users face respiratory sensitisation, and that the environment faces no concern because phytase reduces the phosphorus load. The framework is Regulation (EC) No 1831/2003; Commission Implementing Decision (EU) 2017/302 (BAT 4) names phytase-type additives that reduce total phosphorus excreted.

US: no 21 CFR section, animal-food notices instead#

No phytase has a section in 21 CFR 573 or 558 (eCFR search, 3 November 2026), so access runs through GRAS notices with "no questions" letters and through the AAFCO Official Publication. Four notice groups are recorded.

• AGRN 14 and 15: Citrobacter braakii phytase, poultry 250 to 4,000 FYT/kg and swine 500 to 4,000 FYT/kg.
• AGRN 21, 27 and 32: phytase corn grain, maize expressing an E. coli-derived phytase, poultry 250 to 6,000 FTU/kg and swine 500 to 4,500 FTU/kg.
• AGRN 61: phytase from a Pseudomonas fluorescens strain expressing an altered E. coli appA 6-phytase gene, FDA letter of 2 November 2023.

A "no questions" letter is not an approval and is never transferred to another strain or process; no US withdrawal period applies. The FDA-AAFCO memorandum of understanding ended on 1 October 2024 without a successor. A mandatory GRAS notification is proposed in 91 FR 51834 (11 August 2026, proposed 21 CFR 570.205, comments close 9 December 2026), which lists seven circumstances where no notice is required; it is not final. The wider frame is the US feed additive regulation.

Great Britain and China#

Two other markets keep their own phytase lists:

• Great Britain: the GB feed additive register lists 6-phytase from Aspergillus oryzae DSM 22594 (feedadd-1247) while the EU entry 4a18i names strain DSM 33699 (Implementing Regulation (EU) 2023/1342), and also lists Quantum Blue (feedadd-1248), OptiPhos for fish (feedadd-1243) and the 3-phytase from Trichoderma reesei CBS 528.94 for turkeys for fattening and sows (feedadd-1456).
• China: the China feed additive regulation frame shows an import registration certificate for Ronozyme HiPhos (M), a phytase mixture from Aspergillus oryzae for swine and poultry (Novozymes A/S), valid 2022.12 to 2027.12.

Forms, Grades and Sourcing of Phytase#

Phytase is sold as coated thermostable granulates, powders and liquids for post-pellet application, each with a guaranteed activity per gram or millilitre that has to deliver the act's legal minimum in the final feed. Additive minimums in the acts include 5 000 FTU/g (4a1600) and 30 000 FTU/g (4a37).

Quotes depend on phytase type, form, activity guarantee, matrix support and volume.

Buying checklist for feed phytase#

Before ordering, check seven points:

1. Confirm the identification number, holder and phytase type (3- or 6-phytase).
2. Find the entry for the exact animal category in the EU Register of Feed Additives.
3. Compare the unit and assay named in the act.
4. Ask for thermostability data or a post-pellet liquid.
5. Request a validated matrix for the species.
6. Check the manufacturer's FAMI-QS certification or equivalent quality scheme.
7. For US use, check that the notice covers the notifier's own strain.

Phytase Next to Xylanase, Protease and Inorganic Phosphates#

Phytase acts on phytate, while xylanase, beta-glucanase, beta-mannanase and protease act on other substrates, and feed phosphates supply phosphorus directly. Xylanase acts on arabinoxylans, beta-glucanase on the beta-glucans of barley and oats, beta-mannanase on soybean meal mannans and protease on dietary protein.

Feed phosphates and limestone are feed materials, not additives, and their phosphorus is far more digestible than phytate phosphorus, which is why phytase reduces the feed phosphate needed in a formula. The table compares the classes.

Phytase compared with other enzymes and phosphorus sources

Questions buyers ask about phytase#

Two questions follow.

What is the role of phytase in poultry nutrition?#

Phytase releases phosphorus and calcium from phytate in poultry diets and reduces the phytate that binds minerals, amino acids and energy. Selle and Ravindran (2007) review the evidence, and in the EU its use is bound to the animal categories and legal minimum of the authorising regulation, for example 125 to 500 FTU/kg for chickens for fattening.

How much does phytase cost?#

No dated price is published here; quotes depend on phytase type, form, activity guarantee, matrix support and volume. The request form in the sourcing section collects those points once.