Getting the particle size right in layer mash isn’t just a technical detail – it plays a direct role in how well a hen digests her feed, absorbs nutrients, and ultimately how many quality eggs she lays. Even when a diet is nutritionally spot-on, the wrong mix of fine and coarse particles can quietly hold a flock back.
What is particle size distribution?
Particle size distribution (PSD) simply describes the spread of different sized particles within a feed. For layer mash, the target is a Geometric Mean Diameter (GMD) of approximately 1200 microns (1.2 mm), with most particles sitting in a healthy middle range rather than skewing too fine or too coarse.
The ideal spread looks like this:
- 55–85% of particles between 1.0–3.0 mm
- No more than 10% fine particles (under 0.5 mm)
- No more than 10% coarse particles (over 3.0 mm)
Why particle size affects hen health and performance
A hen’s digestive system relies on a mix of mechanical grinding and enzymatic digestion, and particle size determines how well the two work together.
Coarser particles, particularly whole or cracked grains, keep the gizzard active – stimulating grinding and helping it develop into a strong, well-functioning organ. Fine particles play their own role too, offering more surface area for digestive enzymes to act on so nutrients are released efficiently.
The balance matters more than either extreme. Diets too high in fine particles are linked to a smaller, underworked gizzard and faster gut transit, both of which can reduce how much of the feed a hen actually absorbs. On the flip side, feed that’s too coarse can be harder for hens to consume efficiently, working against them rather than for them. Getting the balance right keeps digestion running smoothly from end to end.
Why coarse limestone matters before lay
Including coarse limestone particles (2-4 mm) in pre-lay diets gives hens a real advantage heading into production. Because the larger particles stay in the gizzard longer, they dissolve slowly overnight, releasing calcium exactly when it’s needed most – during the nighttime formation of the eggshell.
Why hens are picky eaters
Hens naturally prefer larger particles, and this preference only gets stronger as they age. If particle size isn’t well controlled, hens will pick out the bigger, energy-dense pieces and leave the finer particles – the ones carrying essential vitamins and trace minerals – behind. Over time, this selective feeding leads to nutrient imbalances and a drop in performance, even when the diet formulation on paper is correct.
Steps to get particle size right on farm
Keeping particle size consistent takes a bit of ongoing attention, both in the shed and back at the mill:
- Watch the flock. Feed sorting or uneven consumption in the shed can be early warning signs that particle size isn’t quite right.
- Manage feeder timing. Letting feeders run empty at controlled intervals helps stop fine particles building up at the bottom and being left behind.
- Review grinding and screening. Hammer mills or roller mills and their screens need to be set up to consistently produce the target particle range.
- Check mixer performance. A well-mixed batch spreads nutrients evenly through the feed, not just the particle sizes.
- Handle feed carefully after processing. Excess handling, augering, or long transport runs can cause particles to separate out again, undoing good processing work.
- Support good presentation on the farm. Feeder design and day-to-day management should keep the feed consistent right up until the hen eats it.
Getting particle size distribution right isn’t a one-off fix – it’s an ongoing process of monitoring, adjusting, and fine-tuning feed processing and on-farm management. Done well, it supports strong gizzard function, efficient digestion, and consistent egg production and shell quality.
At Reid Stockfeeds we are focused on precision manufacturing, ensuring our mash feeds are produces at the optimal particle size for your herd or flock. We have a number of processes and checks in place that allow us to deliver the right size feed every time.
Chat to us today about what your particle size should be and why! Contact Reid Stockfeeds today on 1300 REID FEED to speak directly with our Monogastric Specialists about our Eggs4Sure range or poultry rations tailored to your exact standards.
Author
AuthorJohnny Barwary
PhD in poultry nutrition and physiology
Reid’s monogastric manager
