Probiotics for Poultry: Strains, Evidence and Use in Broilers and Layers

Probiotics for poultry are live, strain-identified bacteria and yeasts, mainly Bacillus spores, lactic acid bacteria and Saccharomyces cerevisiae, that the EU authorises as zootechnical additives, mostly gut flora stabilisers, with legal minimum contents for chickens for fattening from 3 × 10^7 to 3 × 10^10 CFU/kg complete feed. Each strain has its own minimum, bird categories and end date.

Poultry probiotics belong to category 4, one of the five types of feed additives in Regulation (EC) No 1831/2003. The types of feed additives are defined by function, and "probiotic" is not a legal category among them. Four facts frame the topic.

• EU legal minima for chickens for fattening run from 3 × 10^7 CFU/kg (4b1898) to 3 × 10^10 CFU/kg (4b1708); the overview of direct-fed microbials covers other species.
• No withdrawal period applies to any EU microorganism gut flora stabiliser.
• One probiotic carries an EU Salmonella claim in poultry: 4d1703.
• In the US, no probiotic is FDA-approved; direct-fed microbials are regulated as food under FDA CPG Sec. 689.100.

What Are Probiotics for Poultry?#

In EU law, probiotics for poultry are microorganisms authorised as zootechnical additives, mostly in functional group 4b gut flora stabilisers, which Regulation (EC) No 1831/2003 defines as "micro-organisms or other chemically defined substances, which, when fed to animals, have a positive effect on the gut flora". Three poultry entries sit in 4d other zootechnical additives: 4d1703, 4d1712 and 4d12.

Each authorisation is strain-specific: the strain is species plus deposit number, and the authorisation is bound to its holder under Regulation (EC) No 1831/2003. Yeast cell walls and inactivated bacteria are feed materials (Regulation (EU) 2022/1104), not probiotics.

How Do Probiotics Work in the Chicken Gut?#

Probiotics act in the chicken's intestine by excluding bacteria such as Clostridium perfringens and coliforms from attachment sites, by producing lactic acid, bacteriocins or lipopeptides and by secreting enzymes, and each effect is specific to the strain tested. Gut effects are measured with biomarkers such as villus length, crypt depth and villus:crypt ratio (Ducatelle et al. 2018, Veterinary Research 49:43).

Spores, lactic acid bacteria and live yeast#

Poultry probiotics fall into three groups: spore formers, lactic acid bacteria and live yeast. The groups differ as follows.

• Spore formers (Bacillus, Weizmannia, Clostridium): spores survive pelleting and gastric passage, then germinate in the small intestine.
• Lactic acid bacteria (Enterococcus, Lactobacillus genera, Pediococcus): lactic acid lowers gut pH; cells adhere and exclude competitors.
• Live yeast (Saccharomyces cerevisiae CNCM I-1079): carries an EU Salmonella claim.

Clostridium butyricum, a butyrate-producing spore former, and Enterococcus faecium are not QPS (qualified presumption of safety), while Bacillus subtilis, B. licheniformis, B. velezensis and S. cerevisiae are QPS with qualifications (EFSA, 2025 list).

Which Probiotic Strains Are Authorised for Poultry?#

The EU Register of Feed Additives lists Bacillus and other spore formers, lactic acid bacteria and one single-strain live yeast for poultry, and each entry names its bird categories, its own legal minimum and its own implementing regulation. The table compares the entries as read in the EU Register; three uses past their printed expiry carry a status sentence.

EU probiotic entries for poultry (EU Register and implementing regulations, read 2026-11-03)

Legal minimum content per kg complete feed at 12 % moisture (CFU/L for water for drinking), as set in each implementing regulation; not a recommended dose. No maximum content and no withdrawal period are set for these entries.

Four pages cover the groups in depth.

• Spore formers, strain dossiers: Bacillus probiotics in feed
• Enterococcus, Lactobacillus-genus and Pediococcus entries: lactic acid bacteria in feed
• Saccharomyces cerevisiae strains: live yeast probiotics
• Same strains in other species: probiotics for pigs, probiotics in aquaculture feed

Spore formers form the larger group, from 3 × 10^7 CFU/kg (4b1898, the lowest poultry minimum in the table) to 1.6 × 10^9 CFU/kg (4b1828, 4b1894). Minima differ about 100-fold within one genus. Two names changed: 4b1820 is Bacillus velezensis, renamed from B. subtilis C-3102 by Implementing Regulation (EU) 2022/703, and 4b1900 is Weizmannia faecalis, formerly Bacillus coagulans.

Lactic acid bacteria include three Enterococcus lactis entries (4b1705, 4b1841, 4b1708), multi-strain preparations such as 4b1890 and Pediococcus acidilactici CNCM I-4622 (4d1712, all avian species). The older 4b1707 entry is named in its act as Enterococcus faecium. E. lactis NCIMB 11181 (4b1708) has the highest chicken minimum, 3 × 10^10 CFU/kg.

Saccharomyces cerevisiae CNCM I-1079 and the EU Salmonella claim#

Saccharomyces cerevisiae CNCM I-1079 (4d1703) is the only probiotic with an EU Salmonella claim for poultry: "reduction of Salmonella spp. contamination on carcasses through its decrease in faeces", at min 1 × 10^9 CFU/kg complete feed (12 % moisture), EU legal minimum, for chickens, minor poultry and turkeys for fattening. It runs to 8 November 2027 for chickens (Implementing Regulation (EU) 2017/1905) and 26 February 2030 for turkeys (Implementing Regulation (EU) 2020/162).

The other EU Salmonella-claim additive in poultry, bacteriophages 4d29 in drinking water (Implementing Regulation (EU) 2025/1390), is not a probiotic. In the US, a Salmonella-reduction claim is a drug claim. Programme design is covered under Salmonella control in poultry.

What Does the Evidence Show in Broilers and Layers?#

Meta-analyses of broiler trials show small average gains in body weight and feed conversion from probiotics, with Bacillus more consistent than Lactobacillus, while no laying-hen meta-analysis with verified effect sizes is available. These averages never make probiotics equivalent to antibiotic growth promoters.

Two broiler meta-analyses: Bilal et al. 2026 and Blajman et al. 2014#

Bilal, El-Fateh, Arfan and Zhao (2026, Poultry Science 105(6):106854), pooling 53 studies with 106 broiler trials, found body weight +66.6 g and FCR −0.058 (−0.107 adjusted). The table sets it beside the older Blajman meta-analysis.

Blajman's body weight gain effect was no longer significant after correction for publication bias, and both analyses pooled broilers only. Additives compared on feed conversion ratio are covered separately.

Why poultry responses to probiotics vary#

Responses vary because strain, dose and survival, delivery route and publication bias differ between trials. Vegetative lactic acid bacteria or uncoated yeast added before an 85 to 90 °C conditioner do not keep their label CFU. Against coccidiosis, Peek and Landman (2011) found that prebiotics and probiotics gave conflicting, non-consistent results.

How Much Probiotic Goes into Poultry Feed and Water?#

Each authorised strain must reach its EU legal minimum in the final feed, from 3 × 10^7 CFU/kg (4b1898) to 3 × 10^10 CFU/kg (4b1708) for chickens for fattening, and no maximum content or withdrawal period is set. The only EU microorganism maximum applies to E. lactis DSM 7134 in pigs (Implementing Regulation (EU) 2020/159).

Legal minimum content in feed: the CFU/kg range#

The EU legal minimum is the lowest CFU count the act requires in the final feed, measured per kg complete feed at 12 % moisture. Three points define it.

• A floor, per strain: for example min 1 × 10^9 CFU/kg complete feed (12 % moisture) for 4b1822 under Implementing Regulation (EU) 2020/1395.
• Not an optimum or recommended dose: the act sets no target and no maximum.
• Not transferable: minima differ about 100-fold between strains of one genus.

Probiotics in drinking water: liquid and water-soluble forms#

Only entries whose act sets a CFU/L minimum may be given in drinking water; 4b1713 and 4b1897i are water only. The table lists the water minima.

The 4b1894 (2025/2576) and 4b1897i acts require stability in water for drinking to be stated. Cleaning and treatment of the drinking-water lines themselves is a separate topic that this page does not cover.

Pelleting, premix storage and coccidiostat compatibility#

Spore formers tolerate pelleting, vegetative cells need protection, and each act lists the coccidiostats the strain may be combined with. Compatible coccidiostats are never implied by the genus. EFSA data for one Bacillus preparation show under 0.5 log loss after pelleting at 95 °C and after 6 months in premix at 25 °C and 60 % relative humidity.

Protected forms exist for heat-sensitive cells: 4b1705 as micro-encapsulated granules (at least 1 × 10^10 CFU/g) and 4d1703 as a coated form (at least 1 × 10^10 CFU/g), and the 4d1703 acts require storage conditions and stability to heat treatment on the directions for use.

Act lists differ: 4b1822 (2020/1395) names diclazuril, monensin sodium and nicarbazin; 4b1827i (2021/2051) lasalocid A sodium, monensin sodium and diclazuril; 4b1828 (2021/1410) diclazuril and lasalocid A sodium; 4b1708 monensin sodium and decoquinate; 4b1897 nicarbazin, diclazuril, decoquinate and halofuginone.

Probiotics for Broilers, Layers, Turkeys and Minor Poultry#

EU probiotic authorisations are granted per bird category exactly as the act words it, so a strain authorised for chickens for fattening may not be fed to laying hens unless its act names them. Other poultry feed additives use the same categories, and the overview of poultry feed additives sets out each programme.

The table matches categories to example entries and programme pages.

Chickens for fattening#

Chickens for fattening have the widest choice, from 3 × 10^7 CFU/kg (4b1898) to 3 × 10^10 CFU/kg (4b1708). Four table entries name only this poultry category: 4b1821 (8 × 10^8 CFU/kg, runs to 26 February 2030, Implementing Regulation (EU) 2020/161), 4b1825 (1 × 10^9 CFU/kg), 4b1892 and 4b1713 (5 × 10^8 CFU/L, water only).

Laying hens, pullets and breeders#

Laying hens need an entry that names laying birds; rearing pullets are covered as "chickens reared for laying". 4b1828 covers laying hens at 1.6 × 10^9 CFU/kg to 19 September 2031 (Implementing Regulation (EU) 2021/1410); 4b1822 covers poultry for laying (2026/1036), 4b1823i poultry for laying or reproduction (2026/92) and 4b1894 all poultry species for laying or breeding (2025/2576).

Weizmannia faecalis (4b1900) covers all poultry reared for laying or breeding (2026/553), while 4b1705, 4b1890 and 4b1895 exclude laying birds. The 4b1715 laying-hen use (2015/38) and 4d12 (2016/898) are past their printed expiry and are shown with their register status in the table. No layer meta-analysis with verified effect sizes is available.

Turkeys and minor poultry species#

Turkeys have separate entries with their own minima, for example 4b1830 at 1.25 × 10^8 CFU/kg for turkeys against 2.5 × 10^8 CFU/kg for chickens (Implementing Regulation (EU) 2021/1411). 4b1700i names turkeys for fattening as its only poultry category (1.3 × 10^9 CFU/kg; 6.5 × 10^8 CFU/L water), 4b1827i covers turkeys for fattening under 2021/2051, and 4b1852 and 4d1703 cover chickens and turkeys for fattening. Minor poultry appear in entries such as 4b1829 and 4b1841, and 4b1820 and 4d1712 cover all avian species.

EU and US Status of Poultry Probiotics Side by Side#

In the EU, each poultry probiotic needs a strain-specific implementing regulation that fixes its bird categories and legal minimum, while in the US no probiotic is FDA-approved and direct-fed microbials are regulated as food under FDA CPG Sec. 689.100 when they make no drug claim. The table compares the two systems attribute by attribute.

EU: strain-specific zootechnical authorisations#

Each EU authorisation names the strain by deposit number, the holder, the bird categories, the legal minimum and the end date, and it is bound to that holder. No withdrawal period and no MRL apply, and under Article 13(3) of Regulation (EC) No 1831/2003 the label states only the authorised effect, never a disease claim.

No EU authorisation carries a necrotic enteritis or Clostridium perfringens claim (EU Register, 3 November 2026); feed strategies are compared under necrotic enteritis in broilers. The acts class microbial preparations as potential skin and respiratory sensitisers and require operational procedures plus breathing and skin protection for users; for hazard statements, see the product SDS.

For uses past their printed expiry, the register status reads, for example for 4b1707 (Implementing Regulation (EU) 2015/1053): printed expiry 2025-07-22; the EU Register records a renewal application and still lists the entry pending the Commission decision (Article 14 of Regulation (EC) No 1831/2003).

US: direct-fed microbials under CPG Sec. 689.100#

US poultry probiotics are direct-fed microbials, regulated as food under FDA CVM CPG Sec. 689.100 (issued 2 May 1988, revised March 1995) when the organism is on the AAFCO microorganism list and no drug claim is made. The legal basis is the food definition in FFDCA section 201(f)(3); there is no NADA and no 21 CFR 573 entry for a direct-fed microbial.

A disease or structure/function claim makes the product an unapproved new animal drug (section 501(a)(5)) unless a NADA covers it, and an unlisted organism makes it an unapproved food additive. The label reads "Contains a source of live (viable) naturally occurring microorganisms", naming each species and CFU/g, as in the AAFCO Official Publication.

Live Saccharomyces cerevisiae can be sold in the US as a direct-fed microbial only without a Salmonella claim. Dried Komagataella pastoris yeast (21 CFR 573.587) is non-viable, limited to broiler chickens at no more than 10 % of the formulation, and not a direct-fed microbial.

Great Britain, Canada and India#

Three other markets apply their own rules:

• Great Britain: EU authorisations in force on 31 December 2020 were retained and sit in the FSA register; later EU acts do not apply in GB automatically.
• Canada: each viable microbial strain needs CFIA pre-market registration (RG-1 section 3.22); flora or disease claims make the product a veterinary drug.
• India: IS 1374:2007 Annex C lists probiotics among optional poultry feed additives; see India feed regulation.

Forms, Grades and Sourcing of Poultry Probiotics#

Poultry probiotics are sold as spore powders, micro-encapsulated or coated granules and non-coated forms for water, and the guaranteed CFU per gram has to deliver the act's legal minimum in the final feed or drinking water. Acts set additive minima, for example 1 × 10^10 CFU/g for 4b1820 and 2 × 10^10 CFU/g non-coated for 4d1703.

Quotes depend on strain, form, CFU guarantee and volume; no price is given here.

Buying checklist for poultry probiotic strains#

Before ordering, check seven points:

1. Confirm strain identity by deposit number and current EU name, since labels may lag behind renamings.
2. Find the entry in the EU Register of Feed Additives for the bird category.
3. Compare the CFU guarantee at end of shelf life with the legal minimum.
4. Check heat stability for pelleting, or water stability where the act requires it (4b1894, 4b1897i).
5. Check coccidiostat and acid compatibility in the act, such as formic acid for 4b1821.
6. Ask the manufacturing site for FAMI-QS certification or GMP+.
7. For US use, confirm the live-microorganism label statement and the absence of drug or structure/function claims.

Poultry Probiotics in the Wider Gut-Health Programme#

Probiotics are one feed lever on bird gut health, next to prebiotics, acidifiers, enzymes and essential oils. The overview of gut health in poultry maps where each class acts.

Probiotics are live, with a CFU guarantee; prebiotics are "a substrate that is selectively utilized by host microorganisms conferring a health benefit" (ISAPP, Gibson et al. 2017), and postbiotics "a preparation of inanimate microorganisms and/or their components that confers a health benefit on the host" (ISAPP, Salminen et al. 2021). MOS, inulin, FOS and inactivated bacteria are EU feed materials. The table places probiotics next to related groups and their pages.

Probiotics are one class studied as alternatives to antibiotic growth promoters, never presented as equivalent to them.

Questions buyers ask about probiotics for poultry#

Two buyer questions recur.

What do probiotics do for chickens?#

Probiotics stabilise the chicken's gut flora: Bacillus spores germinate in the small intestine and lactic acid bacteria lower gut pH. In broilers, Bilal et al. (2026) found body weight +66.6 g and FCR −0.058 across 106 trials.

Which type of probiotic is best for poultry?#

No single strain is best; choose one authorised for the bird category, feed form and coccidiostat programme. Bacillus improved FCR more consistently than Lactobacillus (Bilal et al. 2026).