Aluminium-Hydroxide-Adjuvanted Intramuscular Suspension for Replacement Breeding Stock

For replacement gilts and boars entering a porcine breeding unit, the inactivated Haemophilus parasuis bacterin is processed into a sterile aqueous suspension adsorbed onto aluminium hydroxide gel. The terminal injectable product is intended for intramuscular administration, conventionally as a 2 mL dose. Manufacturing must be conducted under EudraLex Volume 4 Annex 2 conditions for veterinary medicinal products, and the final suspension must pass sterility testing according to Ph. Eur. 2.6.1 and USP <71>. Bacterial endotoxin content is monitored by Ph. Eur. 2.6.14; because Gram-negative whole-cell bacterins inherently contain lipooligosaccharide, the release limit is established through batch-constitutive safety data rather than a fixed compendial numerical threshold. The antigen concentrate addition ratio is not a fixed percentage across all bulk sizes. The concentrate is standardised by pre-inactivation viable cell count, typically within 3.0×10⁹–8.0×10⁹ CFU/mL. After inactivation and aseptic harvest, the concentrate is added to the aluminium hydroxide bulk at 10%–20% v/v to achieve a final release specification of 1.0×10⁹–2.0×10⁹ inactivated cells per 2 mL dose. The exact volume fraction is calculated per batch as concentrate volume = final batch volume × (target dose count × batch dose number) / (concentrate cell count × expected antigen recovery).

Downstream production begins with fermentation of Haemophilus parasuis in PPLO broth supplemented with 1% v/v nicotinamide adenine dinucleotide and 5% v/v inactivated horse serum at 37±0.5°C under 5% CO₂ for 18–24 h. The culture is inactivated with formaldehyde 0.2% v/v at 37°C for 24–48 h with agitation at 100–150 rpm; inactivation is confirmed by two blind passages on chocolate agar at 37°C for 7 days. The inactivated bulk is then concentrated or diafiltered to reduce residual formaldehyde and low-molecular-weight medium components. Adsorption onto aluminium hydroxide is performed at pH 6.8–7.2 for 12–24 h at 4–8°C. Terminal product types are aqueous injectable suspensions in 50 mL, 100 mL, or 250 mL vial presentations. A critical process limit is avoidance of aluminium gel flocculation when antigen concentrate is introduced too rapidly; batch records therefore specify that antigen concentrate be diluted 1:5 with sterile buffer before adjuvant mixing.

High-shear rotor-stator emulsification of a pre-farrowing sow vaccine requires the inactivated Haemophilus parasuis bacterin to be incorporated into a sterile aqueous phase before oil addition. The objective of this water-in-oil emulsion presentation is to create an intramuscular depot that prolongs antigen presentation and increases colostral antibody transfer. The aqueous antigen phase typically constitutes 40%–50% v/v of the final emulsion. The oil phase comprises light liquid paraffin and sorbitan monooleate at 8%–12% w/v of the oil phase; primary emulsification is carried out in a high-shear rotor-stator mixer at 8,000–12,000 rpm for 10–20 min, followed by a valve homogeniser pass at 150–250 bar to reduce droplet size below 10 μm Dv90. Compliance requires sterility by Ph. Eur. 2.6.1 and preservative efficacy by Ph. Eur. 5.1.3 when a multidose presentation is selected. The terminal product type is an injectable water-in-oil emulsion, supplied as 2 mL or 5 mL dose vials. Emulsion viscosity is held at 20–40 mPa·s at 20°C to maintain syringeability through 18 G needles. Published data for this specific Haemophilus parasuis water-in-oil configuration is limited; the stated operating ranges derive from general veterinary bacterin emulsion practice and require batch-specific stability verification.

What Limits Antigen Load in Polyvalent Swine Respiratory Co-Formulations?

When an inactivated Haemophilus parasuis bacterin is co-formulated with inactivated Mycoplasma hyopneumoniae or porcine circovirus type 2 subunit antigen, the limiting variable is typically aluminium hydroxide binding capacity rather than bulk volume. The H. parasuis concentrate is added at 10%–18% v/v of the final aqueous bulk after each antigen has been pre-diluted to matched protein content. Potency preservation for each component must be demonstrated by batch-release potency assays rather than by calculation alone; where no compendial potency test exists for the combination, the manufacturer applies consistency protocols under Ph. Eur. 5.2.6 or USDA 9 CFR Part 113. Manufacturing controls include sequential adsorption: Mycoplasma antigen is adsorbed first at pH 6.4–6.8, then the H. parasuis antigen at pH 6.8–7.2, because simultaneous addition produces competitive desorption and free-antigen supernatant fractions above 15%. Terminal product types are multivalent injectable suspensions in 2 mL dose presentations for mass vaccination of grow-finish pigs.

A recognised production-scale failure mode in multi-antigen bacterin lines is the formation of visible aggregates when the H. parasuis concentrate is added at 25% v/v or higher without a 1:10 dilution step. To prevent this, stainless steel 316L mixing vessels of 500–2,000 L capacity are operated with bottom-mounted magnetic mixers at 120–180 rpm, and antigen concentrate is introduced at a maximum rate of 5 L/min per 1,000 L bulk. After adsorption, the bulk is held at 4°C for 8–24 h before filling; samples are drawn from top, middle, and bottom zones to confirm antigen content variance below 5% RSD. The finished multivalent suspension must remain free of visible particulates larger than 25 μm when examined according to the relevant compendial visible inspection procedure.

For closed-herd outbreak control, the inactivated Haemophilus parasuis bacterin is produced as an autogenous injectable aqueous suspension from a diagnostic isolate. The isolate is serotyped by gel diffusion or PCR and expanded in NAD-supplemented broth; because field isolates frequently show slower growth than reference strains, fermentation time may extend to 36 h before reaching a pre-inactivation count of 1.0×10⁹–3.0×10⁹ CFU/mL. Addition ratio in the final formulation is calculated to deliver 1×10⁹ inactivated cells per 2 mL dose; this frequently corresponds to 20%–35% v/v of concentrated antigen suspension in the final aqueous bulk because autogenous harvest titres are lower than commercial fermentation titres. The downstream production process includes formaldehyde inactivation at 0.2% v/v for 48 h at 37°C, sterility and inactivation checks, and aseptic filling into 2 mL or 10 mL vials. Terminal product type is a herd-specific injectable suspension, authorised under national autogenous biological product permits, with expiry typically limited to 6–12 months at 2–8°C. Sterility is confirmed by Ph. Eur. 2.6.1; safety is demonstrated by a target-animal batch safety test according to Ph. Eur. 5.2.6 or the relevant national monograph.

When Oil-in-Water Adjuvanting Replaces Aluminium Gel in Piglet Priming

In piglet priming programmes where injection-site reactivity must be minimised, an oil-in-water emulsion is used instead of aluminium hydroxide. The aqueous antigen phase containing inactivated Haemophilus parasuis bacterin represents 60%–70% v/v of the final emulsion; the oil phase, typically medium-chain triglycerides or squalane, represents 20%–30% v/v with polysorbate 80 at 2%–4% w/v of the oil phase as surfactant. The antigen concentrate addition is adjusted to 10%–20% v/v of the aqueous phase, targeting the same final dose count as the aluminium-adjuvanted product. Downstream production uses a two-step emulsification: a low-shear mix at 500–1,000 rpm for 5 min to form a coarse dispersion, followed by high-pressure homogenisation at 200–400 bar for 3–5 cycles until droplet size Dv90 is ≤5 μm. Terminal product type is an oil-in-water injectable emulsion with lower local reactogenicity, supplied in 2 mL single-dose vials or 50 mL multidose vials. Compliance includes sterility by Ph. Eur. 2.6.1, droplet-size verification by laser diffraction, and bacterial endotoxin by Ph. Eur. 2.6.14. A critical process conflict is heat accumulation during homogenisation; the product temperature must not exceed 25°C because overheating reduces emulsion stability and can denature surface-exposed bacterial antigens. If the homogeniser cooling jacket fails, batch records show visible creaming within 24 h at 2–8°C.