Egg production curves and what breaks them
A layer flock has one shape it is supposed to follow. Reading where yours departs from it tells you what went wrong and roughly when.
Awaiting veterinary review. This guide is written from published industry practice and has not yet been checked by our domain advisor. Confirm anything clinical with your own veterinarian before acting on it.
A broiler flock is judged at the end. A layer flock is judged every single day for over a year, against a curve the breeder published before the birds hatched. That curve is the most useful diagnostic tool a layer farm has, and most farms never plot it.
The shape
| Stage | Roughly | What happens | | --- | --- | --- | | Point of lay | ~18–20 weeks | First eggs, small, irregular | | Rise | 20–26 weeks | Climbs steeply | | Peak | ~26–30 weeks | The maximum — commonly 90–95% | | Persistency | 30–72+ weeks | A slow, steady decline |
Two numbers describe a layer flock: how high it peaks and how slowly it falls. Persistency is worth more money than peak, because it is paid out over fifty weeks rather than four.
Egg size increases throughout, so a flock laying fewer eggs later in life is not necessarily producing less mass.
Rearing decides the peak
By the time a pullet lays her first egg, her peak is largely already set. Body weight and frame at point of lay are what determine whether she can sustain 90%+.
An underweight pullet will never peak properly, no matter what you feed her afterwards. She will come into lay late, peak low, and lay small eggs. Almost every disappointing peak is a rearing failure, not a laying-house failure.
Weigh pullets through rearing against the strain’s target. Uniformity matters as much as the average — a flock where a third of the birds are behind will have a flat, smeared peak instead of a sharp one.
What breaks a curve, and how it looks
A sudden, sharp drop across the flock points to something acute:
- Infectious bronchitis — often with misshapen, thin or wrinkled shells and watery whites
- Newcastle disease — usually with respiratory or nervous signs and mortality
- Heat stress — abrupt, follows the weather, shells thin first
- Water interruption — the fastest and most reversible of all; even a few hours without water costs eggs for days
- A feed change, or a batch of feed that is short on calcium or energy
A gradual failure to hold points at nutrition or parasites:
- Feed intake falling as the weather heats up
- Calcium or available phosphorus below requirement
- Mycotoxins in the ration
- Internal or external parasites
- Lighting drifting shorter
A peak that never arrives points back at rearing.
Light: never go backwards
In layers, day length is the signal for sexual maturity. The rule is simple and absolute in commercial practice: during rear you never increase day length, and during lay you never decrease it.
A shortened day in a laying flock — a timer failure, a load-shedding pattern that eats the morning light — reads to the bird as the end of the season. Birds can go out of production and are slow to come back.
Shell quality tracks separately
Shell quality declines with flock age even when egg numbers hold, because egg size keeps rising while the hen’s ability to deposit calcium does not. Cracks and downgrades are a cost that climbs all the way through the cycle.
Calcium particle size matters here: coarse limestone or oyster shell stays in the gizzard and releases calcium overnight, which is when the shell is actually formed. Fine limestone alone passes through too quickly.
Plot it
One line, daily, hen-day percentage against the strain’s target. Nothing else on a layer farm shows you a problem as early — usually several days before anything is visible in the shed.