Before formulation evaluation, the blended live culture is screened for strain identity, toxigenic potential and antibiotic resistance genes. Bacillus cereus is enumerated on mannitol egg yolk polymyxin agar according to ISO 7932:2004 after heat activation at 80 °C for 10 min to select spores; Streptococcus faecalis (Enterococcus faecalis) is enumerated on bile esculin azide agar according to ISO 7899-2:2000. The release specification allows total Bacillus cereus spore count between 1.0×10¹⁰ CFU/g and 5.0×10¹⁰ CFU/g and Streptococcus faecalis count between 1.0×10⁹ CFU/g and 1.0×10¹⁰ CFU/g. PCR screening must return negative results for the nhe, hbl and cytK enterotoxin gene clusters in the Bacillus fraction and for vanA, vanB and esp in the enterococcal fraction. Moisture is controlled to 6.0% by ISO 6496:1999 or Karl Fischer titration, and water activity is held below 0.35 at 25 °C by ISO 18787:2017. A 1 kg sample pulled from three production lots after 20 min blending in a 500 L twin-ribbon mixer must show a coefficient of variation of live-cell distribution below 0.15 log10 CFU/g. These release thresholds decide which downstream unit operations can be executed without destroying the non-spore-forming Streptococcus fraction, which is more sensitive than the Bacillus spore fraction to heat, high water activity and shear.

What Limits the Post-Pelleting Recovery Window in Broiler Direct-Fed Microbial Premixes?

Dry premix addition to broiler feed is carried out in two dilution stages. A 1 kg API portion is first blended with 9 kg ground limestone or defatted rice bran carrier in a 50 L V-blender for 10 min; the preblend is then added to a 2,000 kg horizontal ribbon mixer and mixed for 15 min at 80 rpm. The final inclusion is 2.5 kg premix per 1,000 kg complete feed, delivering 1.0×10⁸–1.0×10⁹ CFU/kg of total live organisms. Direct addition of the unmixed API to the main mixer without the first dilution step is not accepted, because field-scale distribution tests show hot spots of Bacillus cereus above 3.0×10⁹ CFU/kg and Streptococcus-deficient zones below 5.0×10⁷ CFU/kg. After dry mixing, the feed is sampled at the mixer discharge screw and at the bucket elevator inlet; the live-cell coefficient of variation between these points must be below 0.20 log10 CFU/g.

Pelleting is the critical thermal step for the Streptococcus faecalis fraction. Conditioning at 80 °C for 45 s produces a 1.5–2.5 log10 CFU/g reduction in the vegetative enterococcus; Bacillus cereus spores typically show a lower reduction of 0.5–1.0 log10 CFU/g, but this depends on pellet die friction and conditioning moisture. When finish feed is pelleted, the live blend is therefore not added solely in the dry mixer at full dose; the dose is split, with the Bacillus-dominant dry portion applied before conditioning and the Streptococcus-dominant liquid portion applied after pelleting. The post-pelleting liquid is sprayed onto cooled pellets at 40 °C in a vacuum coater operating at −0.6 bar for 4 min. The spray suspension is prepared at 1.0×10⁹ CFU/mL in potable water containing 0.1% sodium alginate as a droplet stabilizer and is metered at 0.5 L per 100 kg of pellets. If the pellet surface water activity after coating exceeds 0.70, the Bacillus spore fraction germinates in the bag and the product loses spore dormancy within 72 h. The terminal product is broiler crumble or pellet feed in multiwall paper bags with a polyethylene inner liner; finish feed moisture is not allowed to exceed 12.0%.

Swine nursery top-dress granules are made by low-shear fluid-bed spray granulation at 35 °C, because wet high-shear granulation exposes the Streptococcus faecalis fraction to water activity above 0.60 for too long and produces a viability loss of more than 1.0 log10 CFU/g before drying. The binding solution contains 10% pregelatinized starch and 5% maltodextrin in deionized water; the bed temperature is held between 32 °C and 38 °C, and the exhaust air humidity is kept below 45% RH. After drying, the granule moisture is 4.5–5.5%. The product is sieved to retain the 300 μm to 500 μm fraction; fines below 100 μm are recycled at a maximum of 20% of fresh feed mass, because recycled fines carry electrostatic charge and cause non-uniform distribution of the live cells in the final top-dress. A 1:100 preblend with spray-dried whey is prepared in a 100 L paddle mixer for 8 min before final dilution with ground rice hulls or light calcium carbonate. The top-dress is applied at 3 kg per tonne of complete nursery feed and is formulated to deliver 1.2×10⁹ CFU/kg of Streptococcus faecalis and 3.0×10⁸ CFU/kg of Bacillus cereus spores. The terminal granules are coated with 2% hydrogenated vegetable oil at 45 °C in a pan coater to delay moisture uptake; without this coating, nursery feeds containing zinc oxide at 2,000 mg/kg and copper sulfate at 150 mg/kg cause an enterococcus count drop of 0.8 log10 CFU/g within 14 days. Finished granules are packed under nitrogen in 25 kg aluminium-lined bags and stored at 25 °C and 60% RH for a maximum of 180 days.

A Calf Oral Drench Must Not Be Held After Reconstitution

Oral drench powders for calves are reconstituted in warm water at 38 °C to a final volume of 2 L per calf. The powder is compounded in a 200 L low-shear mixer from the live blend, monohydrate lactose and a citrate buffer; on reconstitution the pH is 6.5–6.8. The target dose is 5.0×10⁸ CFU of Streptococcus faecalis per calf per day and 1.0×10⁸ CFU of Bacillus cereus spores per calf per day. Osmolality of the reconstituted drench is measured by freezing point depression and must remain between 300 mOsm/kg and 400 mOsm/kg; above 500 mOsm/kg the vegetative enterococcus cell membrane loses water and the culturable count falls faster than 0.5 log10 CFU/mL per hour. Once reconstituted, the drench must be administered within 4 h; in aqueous media at pH 7.0 and 25 °C, Streptococcus faecalis does not sporulate and begins measurable decline. The drench is not steam-sterilized; any terminal heat treatment above 60 °C for 1 min produces a 3–4 log10 CFU/mL loss in the enterococcal fraction. For milk replacer powder, the product is dry-blended at 1.0×10⁷ CFU/g of milk replacer. Reconstitution is limited to 42 °C; water at 50 °C kills 1.0–1.5 log10 CFU/g of Streptococcus faecalis within 5 min. The reconstituted milk replacer is fed within 30 min, because longer holding at rearing temperature allows Bacillus cereus vegetative growth and possible enterotoxin production. Acidified milk replacer at pH below 4.5 is incompatible with the live Streptococcus fraction; the product should not be added to acidified milk replacer unless a buffer is included. Terminal products are calf oral drench powder and calf milk replacer additive.

If the Preparation Is Suspended in a Vitamin-Electrolyte Oral Solution for Poultry Drinking Water

Dry water-dispersible oral solutions are compounded to be reconstituted in the barn within 4 h before administration. The final drinking water concentration is 1.0×10⁷ CFU/mL. The formula uses a 0.085 M citrate-phosphate buffer to hold pH at 6.5; glucose is limited to 0.5% w/v because higher glucose concentrations raise osmolality above 600 mOsm/kg and reduce enterococcal viability. The dry powder is passed through a 1.5 mm sieve and filled into double polyethylene-lined foil pouches. Chlorinated water inactivates the vegetative Streptococcus fraction; sodium thiosulfate at 0.001% w/v is included as a chlorine neutralizer. Water lines used for the oral solution must not be treated simultaneously with hydrogen peroxide or organic acid salts; acidifiers at pH below 4.5 create an incompatible environment for the enterococcal cell wall. A production-scale drinking water proportioner is calibrated to deliver 0.5 L of stock suspension per 100 L of drinking water; the stock suspension itself is prepared in a 50 L stainless steel tank with gentle agitation at 30 rpm. After mixing, the final solution is used within 24 h; any residual medicated water is discarded and water lines are rinsed with clean water. The terminal product is a water-dispersible oral solution powder for poultry and swine, not a parenteral solution.

Extruded aquaculture feed is not dry-blended with the complete live preparation before extrusion because the extruder barrel and die temperatures of 105–125 °C destroy the Streptococcus faecalis fraction. Post-extrusion vacuum coating is specified instead. The feed pellets are dried to 6–8% moisture and cooled to 45 °C before entering a vacuum coater at 0.4–0.6 bar. Fish oil is used at 6% of pellet mass; the live blend is suspended in the oil with 0.5% lecithin as a dispersant. The oil-bacterial suspension is sprayed at 1.0×10⁹ CFU/mL over 3–5 min. Atomizing air pressure is maintained between 2.0 bar and 3.0 bar; higher pressure above 4.0 bar causes shear-induced loss of 0.9 log10 CFU/g in the enterococcal fraction. Vacuum release pulls the oil phase into the open pores of the pellet. The final target is 1.0×10⁸ CFU/g of finished feed. After coating, pellets are held in a cooling line until the residual surface oil is absorbed and the pellet surface is dry to touch; packaging in woven polypropylene with an inner polyethylene liner is required to prevent water activity increase above 0.60. For shrimp feed, the coated pellets may be crumbled to 0.6–1.0 mm only after oil absorption is complete; premature crumbling releases trapped oil and creates hot spots of bacterial growth. Published survival data for this exact live blend in extruded aquaculture matrices are limited; each feed mill should validate the first three production batches by enumeration at the pellet core and surface. The terminal product is top-coated aquatic feed for shrimp, tilapia and carp.

Compression Behaviour and Roller Compaction Limits for Canine Probiotic Tablets

Direct compression of the API at 20% loading in microcrystalline cellulose is possible, but tablet compaction pressures above 200 MPa reduce Streptococcus faecalis count by more than 2.0 log10 CFU/g. Roller compaction is therefore preferred for high-loading tablets. The dry granulator is run at a roll pressure of 6 MPa and roll speed 10 rpm; the compacted ribbon is milled through a 1.0 mm screen. The granulate is blended with 0.5% magnesium stearate for 2 min; longer blending at 60 rpm reduces enterococcal viability by 0.2 log10 CFU/g for each additional 5 min. Compression is performed on a 10-station rotary tablet press at 12 kN compression force and 30 rpm turret speed. Final tablet hardness is maintained at 60–80 N; tablets below 50 N show edge friability above 1.0% and tablets above 100 N show delayed disintegration. The process loss is 0.3 log10 CFU/g during roller compaction and 0.4 log10 CFU/g during compression; an overage of 0.7 log10 CFU/g is added to the granulation blend. Capsules are filled using a low-vibration dosator capsule filler at 250 mg fill weight in hypromellose capsules, with the same overage. The terminal product is packaged in polyvinylidene chloride-coated aluminium blister packs with silica gel desiccant; water activity is held below 0.25 and storage is rated for 24 months at 25 °C and 60% RH.

Injectable presentation is outside the intended use of this live culture blend. Because the Bacillus spores are the intended active, a 0.2 μm sterilizing-grade membrane retains the spore fraction; the resulting filtrate lacks the Bacillus component and cannot be considered the same preparation. If the retentate is used, it is non-sterile. Terminal moist-heat sterilization at 121 °C for 15 min achieves a 6 log10 reduction of Bacillus spores but also inactivates the non-spore-forming Streptococcus faecalis. Enterococcus faecalis is not a recognized injectable probiotic; systemic administration of live enterococci carries a risk of bacteremia and endocarditis. Strains carrying vanA or vanB glycopeptide resistance determinants are excluded from feed uses by EFSA QPS guidance. No pharmacopoeial monograph exists for a sterile injectable suspension of live Bacillus cereus and Streptococcus faecalis. If an injectable product is requested, the live API must be segregated from oral and feed-grade supply chains and handled as a biological investigational medicinal product; it is not suitable for routine veterinary injection. The same restriction applies to any solution presented in ampoules, vials or syringes; only oral solutions and drinking water dispersions fall within the technical scope of this preparation.