At a glance. Use daily mortality and culling records to identify changes that warrant investigation, and prepare useful information for the flock veterinarian.
Every farm records mortality, but few farms truly read it. Written down as a simple daily count, those numbers look like a sad list. Plotted as a curve over the life of the flock, they become one of the most powerful diagnostic tools you own. A normal flock does not lose birds at a flat, even rate - the losses cluster into humps and peaks whose timing and shape reveal the cause. A spike at day 3 means something very different from a slow climb in week six. Learning to read that curve lets you diagnose problems by age, often before a single bird is sent to the lab. This guide teaches you how.
Why the Mortality Curve Is a Diagnostic Tool
Mortality is not random noise. Different causes of death strike at characteristic ages, so the timing of a loss is itself a clue. Yolk-sac infection kills in the first days; coccidiosis strikes in mid-cycle; prolapse builds late in lay. Plot deaths against age and these patterns separate themselves out.
The curve turns a raw number into a question with a likely answer. Instead of asking only "how many died," you begin asking "when, and in what shape" - which points toward why.
- Each cause of death has a typical age window
- Timing of losses is a diagnostic clue in its own right
- The shape of the curve narrows down the likely cause
- Reading age patterns often beats guessing at symptoms
- The curve guides where to focus necropsy and testing
What a Normal Curve Looks Like
A healthy flock's mortality curve is not flat. It typically shows a small hump in the first week, settles into a low steady baseline through the middle of the cycle, and then, in long-lived layers, drifts gently upward with age. Knowing this normal shape lets you spot the abnormal instantly.
The goal is not zero mortality, which is unrealistic, but a curve that stays within expected bands and shows no sudden, unexplained departures.
- A modest first-week hump is normal and expected
- A low, steady baseline should follow through mid-cycle
- Layers show a slow late-life rise as birds age
- Deviations from this shape are the warning signs
- "Normal" is a recognisable pattern, not a flat line
The Day-3 First-Week Peak
First-week mortality is naturally the highest of the whole grow-out, and it commonly peaks around day 3. That timing is a signature: it points to problems the chick brought with it or met in its first hours - yolk-sac infection, omphalitis (unhealed navels), weak or poor-quality chicks, chilling in transport or brooding, and starve-out where chicks never find feed and water.
A good target for first-week mortality is under about 1%. When the peak is sharp and centred on day 3, look upstream to the hatchery and to your brooding setup.
- First-week losses are naturally the highest of the cycle
- A peak around day 3 points to hatchery and early-brooding causes
- Yolk-sac infection, omphalitis and poor chicks cluster here
- Chilling and starve-out add to the day-3 hump
- Aim to keep first-week mortality under about 1%
These early benchmarks are reference figures - confirm realistic targets for your chicks and climate with your local veterinarian or hatchery.
Early Brooding Losses and Their Causes
Beyond the day-3 peak, the first two weeks carry more losses driven by infection taking hold in naive chicks. Salmonella, E. coli and lingering yolk-sac problems can push early brooding mortality to around 2-3%. Strikingly, this early window can account for roughly 30% of a flock's total mortality for the entire cycle.
That concentration is why brooding gets so much attention. Get the first two weeks right - clean chicks, warm dry litter, easy access to feed and water - and you protect a large share of the flock's survival.
- Salmonella, E. coli and yolk-sac infection drive early losses
- Early brooding mortality can run about 2-3%
- This window may equal roughly 30% of total cycle mortality
- Chick source, warmth and hygiene decide much of the outcome
- Strong brooding pays back across the whole grow-out
Mortality percentages vary widely between farms and strains; treat these as reference figures and confirm your own targets with your veterinarian.
The Mid-Cycle Hump
After the early period settles, a well-run flock enjoys a quiet stretch - until the mid-cycle, when a second hump often appears. This is the window for coccidiosis, Mycoplasma and other respiratory disease, and sudden-death syndrome in fast-growing birds. Mid-cycle losses can run around 3% and account for roughly 35% of total mortality.
A rising curve in this middle window is your cue to look hard at gut health and air quality. Coccidiosis in particular tends to climb over several days rather than spike overnight.
- The mid-cycle hump signals coccidiosis, respiratory disease or sudden death
- Mid-cycle losses can run about 3% of the flock
- This window may make up roughly 35% of total mortality
- A slow climb here often means coccidiosis or Mycoplasma
- Gut health and air quality are the first things to check
As always, these figures are reference points that shift with breed, season and region - verify the picture for your flock with your local veterinarian.
Late-Cycle Losses in Layers
In long-lived laying flocks, a third pattern emerges late: a slow, grinding rise in mortality tied to the demands of sustained egg production. Prolapse, cannibalism, fatty liver haemorrhagic syndrome and egg peritonitis all build gradually rather than striking all at once.
Because these losses accumulate quietly, they are easy to underestimate. Watching the late curve helps you catch problems like pecking or body-condition issues before they snowball.
- Prolapse and cannibalism climb slowly in late lay
- Fatty liver and egg peritonitis add to late losses
- These causes build gradually, not in sudden spikes
- Body condition and lighting management influence the trend
- A creeping late rise deserves attention before it accelerates
Reading the Shape - Spike Versus Slow Climb
Once you know the age windows, the shape of the curve refines the diagnosis. A sudden vertical spike suggests an acute event - an infectious disease outbreak, a heat episode, a water failure, or a management error. A slow, steady climb points instead to a chronic or building problem such as coccidiosis, a nutritional issue, or creeping disease pressure.
Reading shape and timing together is far more informative than either alone. The "when" narrows the cause; the "how fast" confirms it.
- A sharp spike means an acute event - disease, heat, or equipment failure
- A slow climb means a chronic or building problem
- An early hump points to hatchery and brooding causes
- Combine timing and shape to narrow the diagnosis
- Any sudden departure from the baseline warrants immediate investigation
Benchmarks by Bird Type
Numbers only mean something against a benchmark. For broilers, total mortality under about 5% across the cycle is a common target for a healthy flock. For layer rearing, aim for under roughly 3-4% through the growing period. Knowing these bands tells you whether your curve sits in acceptable territory or is drifting into trouble.
Use benchmarks as a scoreboard, not a straitjacket - genetics, climate and market conditions all shift the realistic target.
- Broiler total mortality target: under about 5% for the cycle
- Layer rearing target: under roughly 3-4%
- Benchmarks show whether your curve is on track
- Local conditions and genetics shift the realistic numbers
- Compare flock to flock on your own farm for the clearest signal
These benchmark percentages are reference figures - confirm the right targets for your birds and region with your local veterinarian.
Separating Mortality from Culling
A clean curve depends on clean records, and that means separating true mortality from culling. Culling - or "dumping" - unthrifty, injured or sick birds is a normal part of good management, but if those culls are lumped into the death count, the curve becomes muddy and hard to read.
Record culls in their own column. A flock with rising culls but steady deaths tells a different story from one with rising deaths - and you can only see that difference if the two are kept apart.
- Culling weak or sick birds is normal, deliberate management
- Record culls separately from birds that died on their own
- Mixing the two blurs the diagnostic value of the curve
- Rising culls versus rising deaths point to different problems
- Clean, split records make the curve honest and readable
The Danger of Reflex Medication
When chicks start dying in the first days, the instinct is to reach for antibiotics. Resist the reflex. Over-medicating in the first 2 weeks can damage the developing liver and kidneys - the very organs a young bird needs to grow. Dosing before you know the cause can harm the flock and mask the real problem.
Diagnose first, treat second. A necropsy and a look at the curve often reveal that the losses are non-infectious - chilling, starve-out, poor chicks - where an antibiotic does nothing but harm.
- Avoid reflexive antibiotic use in the first 2 weeks
- Over-medication can damage young liver and kidney function
- Dosing before diagnosis can mask the true cause
- Many early losses are non-infectious and need management, not drugs
- Diagnose first, then treat on evidence
Any medication note here is a general reference point only - always confirm the diagnosis and any treatment with your local veterinarian and respect withdrawal periods.
Daily Records and Necropsy Discipline
None of this works without discipline. The curve is only as good as the daily habit that builds it: count deaths and culls every single day, by house, and plot them. Pair that with routine necropsy of birds that die, and you close the loop between the pattern on paper and the lesion in the bird.
Necropsy turns a shape into a name. A day-3 peak plus unhealed navels and infected yolk sacs at necropsy is a complete diagnosis - curve and carcass agreeing.
- Record deaths and culls daily, house by house
- Plot the numbers so the shape becomes visible
- Perform routine necropsies on birds that die
- Match necropsy findings to the curve's timing and shape
- Consistent records make every flock a lesson for the next
Acting on What the Curve Tells You
Reading the curve is only useful if you act. An early hump sends you back to the hatchery and brooder; a mid-cycle climb sends you to gut and air quality; a late rise sends you to body condition and pecking. The curve is a map that tells you where to look and how urgently.
Over time, comparing curves flock after flock turns your farm's own history into your best diagnostic reference - more relevant than any textbook average.
- Let the timing of losses direct where you investigate
- Match your response to the shape and age of the problem
- Use the curve to prioritise urgent versus building issues
- Build a library of past curves for comparison
- Turn each flock's pattern into a lesson for the next
Your mortality record is already telling a story every day - the skill is in reading it. If you would like help setting up housing, brooding and equipment that keeps that curve low and its early hump small, our team is glad to work through a plan shaped to your birds, your climate and your goals whenever you are ready to design it together.
Visual checklist
Related reading
All-In-All-Out Poultry Management and Downtime
Poultry Respiratory Health: Prevention and Monitoring
Further reading
Disease prevention and treatment must be adapted to the flock and local requirements. Confirm medicines, vaccines and disinfectant procedures with the responsible veterinarian and the approved product instructions.
