Native maize starch is introduced at 5–15% w/w as an intragranular binder-disintegrant in wet-granulated oral tablets for companion animals. The fraction retained on a 75 µm sieve should be below 1.0% when pregelatinised starch is used as a disintegrant, while native starch paste grades are typically released with a loss on drying of 10–14% w/w and a swelling capacity between 18 g/g and 25 g/g at 95°C. Aqueous starch slurry at 5–10% w/w solids is heated to 70–80°C under low-shear mixing until a translucent paste is formed; for maize starch, measurable viscosity peaks between 68°C and 72°C, and holding above 95°C for more than 30 min causes amylopectin scission that reduces intragranular bond strength. Because the material is supplied as a veterinary-grade starch with compendial release testing, botanical source, loss on drying, sulfated ash, and microbial limits should be checked against the relevant Ph. Eur. starch monograph before use.

The wet mass after paste addition is granulated to a final moisture content of 12–15% w/w; overwetting beyond 17% w/w produces dense, slow-disintegrating granules because starch hydrate films fuse at dried particle contacts. The granulate is passed through an oscillating granulator fitted with a 1.2–2.0 mm screen and dried in a fluid-bed dryer at 50–60°C inlet air until residual moisture reaches 2–4% w/w. Compression on a rotary tablet press is performed at 10–20 kN main force to a target breaking force of 5–12 kp; friability is held below 1.0% under USP <1216>. Disintegration testing in purified water at 37±2°C should give a result not exceeding 15 min under USP <701>, and the active-containing tablet must additionally satisfy USP <711> dissolution acceptance criteria because starch hydration at granule interfaces can retard drug diffusion; the effect should be evaluated against a starch-free control because published data for this specific configuration is limited.

Starch-based wet granulation is unsuitable for actives that hydrolyse in the presence of free moisture; in such cases pregelatinised starch at 2–5% w/w is used as an intragranular dry binder with limited aqueous granulation fluid. Compression room temperature should remain below 40°C on the die table because starch film adhesion to punch faces increases beyond this point and produces picking. Finished tablet monographs for veterinary oral anthelmintics and non-steroidal anti-inflammatory drugs frequently list maize starch or pregelatinised maize starch in the formulation dossier, with the starch fraction declared as an excipient because it has no primary pharmacological effect at these use levels.

Because raw starch powder with a fines fraction above 30% flows poorly on automatic capsule equipment, encapsulation-grade starch is usually converted by roller compaction into a free-flowing granulate with a target D50 between 100 µm and 500 µm and a fines content below 15%. Powder flow is characterised by angle of repose between 30° and 35° and Carr index not exceeding 20% according to USP <1174>. Capsule filling on a dosator or tamping-pin machine is run to a fill-weight relative standard deviation below 2.0%; the starch component is commonly used at 20–40% w/w in the fill formulation, with the balance divided between crystalline diluent, disintegrant, and lubricant.

Roller compaction at 4–6 kN/cm ribbon force is adjusted to avoid excessive granulate hardness that reduces compactibility in the capsule slug; overcompaction can raise the fraction of particles above 710 µm and cause incomplete capsule filling. Moisture content is maintained at 8–12% w/w because starch below 8% becomes electrostatically charged and adheres to gelatin or HPMC capsule shells, while moisture above 12% softens the shell at the body seam. Finished capsules containing starch-based fill are tested for in-vitro release under USP <711> and microbial limits under USP <61> and USP <62>. Terminal products include hard-shell oral capsules for companion-animal antibiotics and anthelmintics where the starch filler contributes to plug formation without delaying dissolution beyond the specification.

Can Native Starch Function as a Lyophilisation Scaffold in Sterile Veterinary Suspensions?

Native starch is water-insoluble; injectable use is therefore confined to sterile suspension forms and lyophilisation matrices, never to intravenous solutions. For a sterile aqueous suspension for intramuscular or subcutaneous use, particle-size distribution is controlled by laser diffraction under USP <429> with D90 below 40 µm in screening studies, although published data for starch-containing veterinary injectable monographs is limited. The finished injectable must pass particulate-matter testing under USP <788>, sterility testing under USP <71>, and bacterial endotoxin testing under USP <85>. Because starches of botanical origin carry processing bioburden and endotoxin load, depyrogenation cannot be omitted, and the washed starch must be dried and milled in a controlled area with final-filtered air.

Terminal sterilisation of dry starch is commonly performed by gamma irradiation at 15–25 kGy; doses above 25 kGy reduce molecular weight, increase cold-water solubility, and lower swelling capacity. Moist-heat sterilisation at 121°C for 15 min is not applicable because wet starch gelatinises into a hard cake, while dry-heat sterilisation at 160°C produces browning and loss of binder functionality. In lyophilisation, starch at 5–10% w/w of the pre-lyophilisation dispersion acts as a bulking scaffold; the frozen dispersion is annealed and then dried with a primary shelf temperature below the collapse temperature, commonly -25°C to -15°C, determined by freeze-drying microscopy. Because native starch does not dissolve, the pre-lyophilisation dispersion must be continuously stirred to avoid sedimentation and batch stratification in unagitated vessels.

The reconstituted suspension is assessed for syringability with a 21-gauge needle and for resuspendability after storage at 2–8°C. Starch-based injectable presentations are not appropriate where intravenous administration is required or where the animal species has impaired clearance of insoluble particles; the formulation dossier must justify the route and particle size. Terminal products are therefore sterile suspensions for intramammary or topical injection and lyophilised powders for reconstitution into oral or parenteral suspensions after veterinary prescription.

Particle-Size Matching and Segregation Control in Oral Powder Blends

At a starch carrier level of 10–30% w/w in oral powders, the predominant failure mode is particle-size-induced segregation. The starch fraction should have a D50 between 75 µm and 150 µm when the active premix has a D50 between 100 µm and 250 µm, and the ratio of active D50 to starch D50 should remain below 2:1. A tumble blender with a working-volume fill of 50–70% and a speed of 10–20 rpm for 15–25 min normally achieves a content uniformity RSD below 5.0% when sampled under USP <905>. Bulk density of the starch component is typically 0.45–0.60 g/cm³, which determines sachet fill volume; tapped density is measured to prevent underfilling in high-speed vertical form-fill-seal machines.

Humidity control is a process boundary. Native starch equilibrates above 12% w/w moisture when exposed to relative humidity above 60%, and the resulting liquid bridges produce lumps and restart flow problems in dosing augers. Powder packaging areas are kept at 25°C/40% RH maximum, and finished sachets are made from aluminium foil laminate or HDPE with moisture vapour transmission below 0.1 g/m²/day if a desiccant is not used. The terminal powder blend is tested for loss on drying by USP <731>, content uniformity by USP <905>, and microbial limits by USP <61> and USP <62>. Oral powders prepared with starch carriers are commonly administered by top-dressing onto feed or by dissolution in drinking water for poultry and swine.

The control matrix for non-sterile oral powders is consolidated below.

Granule Porosity Depends on Gelatinisation Kinetics Rather Than Impeller Speed Alone

In veterinary granules for top-dress administration, the starch fraction is used at 20–40% w/w; granule porosity, which controls dispersion in saliva or gastric fluid, is governed more by the gelatinisation state of the starch binder than by high-shear impeller energy. A high-shear mixer granulator is run at an impeller speed of 200–400 rpm and a chopper speed of 1000–3000 rpm; pregelatinised starch binder is sprayed as a 5–10% w/w solution at 10–30 g/min until a wet-mass endpoint of 10–15% w/w water is reached. The wet granules are transferred to a fluid-bed dryer with an inlet air temperature of 60–70°C and dried to residual moisture of 3–5% w/w. The dried product is sieved to a target fraction between 500 µm and 1000 µm, and granule friability is kept below 5% after 10 min of tumbling to limit fines generation in packaging and in feed mixing.

Higher pregelatinised starch binder levels increase dry granule tensile strength but can reduce the rate of active release because the hydrated gel layer forms a diffusion barrier. A granule containing 25% w/w pregelatinised starch may show a dissolution rate reduction of 10–20% relative to 10% w/w binder when measured under USP <711> in species-relevant media. To compensate, sodium starch glycolate or crospovidone is added at 2–5% w/w as an extragranular disintegrant while the native starch fraction remains primarily a granulating diluent. Drying conditions must avoid case hardening, which occurs when the inlet air temperature exceeds 70°C at high humidity and produces a dry outer shell with a wet core; the result is delayed disintegration and localized microbial risk because core moisture remains above 5% w/w.

The terminal granules are filled into single-dose sachets or bulk containers for oral administration to horses, cattle, or companion animals. The finished granules are tested for loss on drying, uniformity of dosage units under USP <905>, and dissolution under USP <711>. Because starch-based granules are hygroscopic, containers must include a desiccant if the closure system has a moisture vapour transmission rate above 0.2 g/m²/day.

A horizontal ribbon blender with a working-volume fill between 60% and 80% is the standard equipment for starch-built medicated premixes. Starch is added at 2–10% w/w as a flow aid and dust suppressant, and the total batch is mixed at 20–30 rpm for 8–12 min. Homogeneity is evaluated by taking 10 discrete samples and assaying the active; the coefficient of variation must remain below 5% for release. Starch with moisture above 12% w/w creates liquid bridges between particles and increases segregation risk in downstream hopper discharge, while starch with a D50 below 50 µm can form dust layers that deposit on dust-collection ducting and create cross-batch contamination.

Regulatory release of a medicated premix containing starch must reference FDA 21 CFR 225 current good manufacturing practice for medicated feed, and, where applicable, EU 2019/4 requirements for medicated feed and intermediates. The starch is declared as an excipient or technological additive according to the filing jurisdiction, not as an active ingredient. In premixes containing copper sulfate pentahydrate or zinc oxide, free moisture from starch can accelerate contact degradation of trace minerals during storage at 40°C/75% RH for 6–12 weeks; moisture-activated discoloration and potency loss are controlled by keeping the premix moisture below 8% w/w. Terminal premix products are diluted into complete feed for swine, poultry, and ruminants at rates determined by the active veterinary substance.

When Pregelatinised Starch Replaces Xanthan Gum in Oral Drench Vehicles

Because native starch is insoluble in cold water, oral solutions and drench vehicles require pregelatinised starch that hydrates without cooking. Dispersed at 2–5% w/v in purified water at 20–25°C, pregelatinised starch forms an opaque pseudoplastic dispersion with a viscosity of 50–200 mPa·s at 20 rpm on a Brookfield viscometer under USP <911>. The system is not a true solution, so clarity and filterability tests are not part of the specification. Viscosity is stable over a pH range of 4.0–7.0; above 8.0, alkaline hydrolysis reduces chain length and suspension capacity within hours at elevated temperature.

In oral drench vehicles for calves, sheep, and goats, pregelatinised starch can serve as an alternative thickener but has a defined limitation: freeze-thaw stability is inferior to xanthan gum, and a starch-thickened vehicle may phase-separate after storage at -20°C. Preservative efficacy must be revalidated because benzalkonium chloride and other cationic preservatives may partition onto starch granule surfaces; antimicrobial effectiveness is tested under USP <51>. The finished oral liquid is filled as a single-dose drench or multi-dose bottle and tested for deliverable volume, viscosity under USP <911>, and content uniformity under USP <905>. Terminal products include oral drenches and tubing liquids for large animals, with the starch component functioning as a suspending body and viscosity modifier rather than a solubiliser.