Animal Feed Pellet Hardness Tester — Crush Strength + Holmen Durability for Poultry, Swine, Aquaculture
Animal feed pellets must survive bagging, augering, conveyor handling, transport to the farm, and final mechanical feeding before the animal eats them. Weak pellets generate fines that segregate during transport, leading to nutrient inhomogeneity, dust hazards in the barn and waste in the feed pan. Two complementary tests measure pellet integrity: crush strength (force to fracture a single pellet) and durability (mass loss under tumbling, the Holmen or PDI test). A reliable feed pellet hardness tester covers both for a complete picture of pellet quality.
Quick Answer
A feed pellet hardness tester measures the compressive force a single feed pellet withstands before fracture, typically reported in kilograms-force (kgf) or newtons. The KHT crush-strength method uses a parallel-platen compression test analogous to ASTM D4179. For durability, the industry uses the Holmen NHP100/NHP200 tumble test or the Kansas State PDI box, which measures mass loss after a defined tumble. A complete feed-mill QC program runs both crush strength and durability on every batch.
Why Feed Pellet Quality Decides Animal Performance and Mill Profitability
Pellet hardness is one of the most critical characteristics indicating process quality, and it is essential to ensure a desirable product and efficient downstream processes. Hardness is the force necessary to crush a pellet, and durability is the amount of fines returning from pellets after being subjected to mechanical or pneumatic agitation. Fines in the feed pan are eaten preferentially by some species and rejected by others — segregating the diet from the formulation specification. For broilers and layers, fines below 10% are typical specification; above 15% the feed conversion ratio measurably worsens. For the feed mill itself, weak pellets are a direct cost: they generate dust hazards, require more frequent cleanout of conveyors and bagging equipment, and produce returned shipments when the customer rejects on dust content. Crush strength and durability QC are the primary tools for catching weak runs before they leave the mill.
Crush Strength vs Durability — Two Different Tests, Two Different Failure Modes
Crush strength measures the compressive force a single pellet withstands at the moment of fracture — the test answers 'how hard is this pellet?'. Durability measures the cumulative mass loss when many pellets are tumbled together — answering 'how much fines does this batch generate during handling?'. They are correlated but not identical: a pellet can have high crush strength (binder is stiff) but low durability (binder is brittle), or vice versa. Two measurement methods dominate feed-mill QC: **Crush strength**: parallel-platen single-pellet test, force-displacement curve to fracture, typical force range 1–60 N for animal-feed pellets. Method analogous to ASTM D4179. **Durability**: Holmen NHP tester (UK industry standard, commonly NHP100 portable or NHP200 lab) or the Kansas State PDI box (KSU PDI). Both tumble a pellet sample under air or mechanical agitation for a defined time, then sieve and weigh the surviving fraction. Typical specs: 95–98% PDI for high-quality broiler feed, 88–92% for cattle feed, > 99% for premium salmon aquafeed.
Crush Strength Method on the KHT Tester
The KHT instrument runs feed-pellet crush strength using a parallel-platen test geometry analogous to ASTM D4179. A single pellet is placed between platens and compressed at 5–10 mm/min until fracture; the peak force is recorded as the crush strength. Typical feed-pellet crush specs are 1–10 N for soft layer mash pellets, 10–30 N for poultry grower, and 25–60 N for premium aquafeed where the pellet must survive pneumatic feeding through long pipes. A precision 0–100 N load cell (with ±0.2% accuracy at this range) handles the full feed-industry span. The 25-position rotary auto-feeder runs an unattended batch in 8–12 minutes, with mean, median and lower-5th-percentile statistics auto-computed and exported to CSV/PDF. Run daily as part of the every-shift QC routine, the same instrument doubles as the device for new-formula development testing.
Durability Testing — Holmen NHP and Kansas State PDI
Pellet durability is measured by tumbling a pellet sample and reporting the percentage that survive the tumble at the original size. The Holmen NHP100 (portable, mill-floor) and NHP200 (lab-grade) are the dominant instruments in European and Latin American feed mills. The Kansas State PDI box (a rectangular tumbling box, 500 g sample, 10-minute tumble at 50 rpm) is the standard in North American mills. The two methods give different absolute values for the same pellet — Holmen tends to report 1–3 percentage points lower than KSU PDI on the same sample because the Holmen air-current adds an attrition component on top of the mechanical tumble. Both methods are valid; the rule is to pick one and stay consistent across all production lines and customer specs. KHT does not currently manufacture the Holmen drum (TEKPRO holds that license) but our crush-strength instrument complements either Holmen or KSU PDI as the second test in a complete QC routine. Many feed-mill QC labs run KHT crush + Holmen NHP100 side-by-side and find the combined data set covers all customer-spec questions.
Where Feed Pellet Crush + Durability Matter Most
Crush and durability QC are most critical for premium and export feeds. Pneumatic-fed aquaculture pellets travel up to 100 m through farm pipes at velocities that fragment weak pellets — salmon and shrimp feeds typically spec >99% PDI and >40 N crush. Long-distance broiler-feed shipments to Africa and the Middle East face 20+ days of ocean transit and multiple trans-shipments — these specs typically demand >95% PDI and >20 N crush. Companion-pet kibble similarly demands high integrity for retail-bag presentation. An Aqua Feed Mill in Southeast Asia used the KHT crush-strength tester paired with a Holmen NHP100 to track the pellet-quality response to a binder reformulation. The new binder lifted PDI from 96.8% to 98.6% and crush strength from 31 N to 42 N — eliminating customer fines complaints and supporting a $50/ton premium for the upgraded product.
Building a Feed-Mill QC Routine for Crush + Durability
A complete feed-mill QC routine uses crush strength and durability as complementary indicators. Recommended frequency: durability (Holmen or KSU PDI) every shift on every production line, crush strength every shift on premium and export lines, plus every formulation change. Both tests are run at the same physical lab bench and entered into a single QC database for trend analysis. KHT software supports trend dashboards that plot crush strength vs PDI over time, with auto-alerts when either trend approaches the lower spec limit. Most feed-mill QC managers use these dashboards to predict the next 4–8 hour pellet-quality direction and trigger preemptive die or roller adjustments before the values drop below spec — a far less disruptive intervention than waiting for a sub-spec lot to be flagged after the fact.
Choosing the Right Feed Pellet Hardness Tester
For animal-feed QC, the recommended configuration is a 0–100 N high-precision load frame (0–500 N option for very hard aquafeed and ruminant pellets), parallel platens flat to ≤5 µm, a 25-position rotary auto-feeder, and software with the durability trend-dashboard module. Pair the instrument with a Holmen NHP100 (portable) or KSU PDI box (lab-grade) for durability — both run as separate workstations and feed data into the same KHT software for combined reporting.
Frequently Asked Questions
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