Most broiler mortality is not random. The common causes — heat stress, respiratory disease, coccidiosis and gut problems, drinker failure, and congenital or cardiac issues — each leave a pattern: a time of day, an age window, a house pattern. Reading that pattern is what turns a spike from a surprise into a diagnosis. This page covers the causes growers actually see, the signature each one leaves in the record, and the checks that separate them — with the money math that shows why the difference matters before settlement.
What Are the Most Common Causes of Broiler Mortality?
| Cause | Typical Signature | First Checks |
|---|---|---|
| Heat stress | Losses climbing in afternoon heat; birds panting, spreading from feeders; water intake spiked hours earlier | House temperature at bird level, tunnel ventilation and cooling pads, water chart deviation |
| Respiratory disease (often ammonia-linked) | Morbidity before mortality — rales, labored breathing, reduced intake; losses spread across a house, not clustered | Ammonia level at bird level, ventilation settings, litter condition (litter ammonia guide) |
| Coccidiosis and gut disease | Bloody droppings, ruffled birds, uneven growth preceding deaths; often peaks weeks 2–4 | Litter caking and moisture, drinking water quality, recent ration or medication changes |
| Drinker failure / starvation | Sudden mortality spike within 24–48 hours of a line problem; small birds hit first; crop-empty birds at necropsy | Nipple pressure and height, line level, pump and regulator, recent line work |
| Ascites, roundheart, other cardiac | Sudden deaths in fast-growing birds, often week 4+, sometimes with pale combs; more common in high-altitude or cold-stress periods | Growth rate vs target, house temperature swings, ventilation adequacy |
| Trauma and handling | Isolated deaths near equipment, fans, or during catch; bruising found at processing | Fan guards, heater clearance, penning and handling practices |
Why the Pattern Matters More Than the Count
A daily count tells you how many died. The pattern tells you why: mortality that climbs every afternoon after the house passes 85°F is heat stress with a ventilation fix — not a disease with an expensive treatment. Losses confined to one house point local: a drinker line, a heater, a cold corner. Losses spread evenly across houses point systemic: ration, chick quality, or a complex-wide health event. And morbidity the flock survives — birds that ate less, gained slower — still steals performance: a flock running 10% light at day 42 from subclinical respiratory pressure has already lost roughly 19,200 lb across 30,000 birds before a single bird dies of it. See the growth bands guide for what that shortfall costs.
When Mortality Spikes: Decision Tree
Pull mortality by house, by day, and by time of day from your logs. Normal post-week-1 mortality runs well under 1% per week; anything above that, or any sudden day-over-day doubling, earns investigation. Compare houses under the same weather before treating it as a farm-wide problem.
Temperature across the floor (not just at the controller), panting behavior, feed and water access, litter condition, air quality. Heat stress and drinker failure are the two causes that announce themselves physically — and both have hours, not days, to fix.
Water deviation precedes most crises: a spike before a heat event, a drop before a drinker failure or disease onset. Compare against the water chart and the feed chart for the age. Feed normal + water down = water system. Both down = environment or health.
Pattern, affected houses, water and feed deviations, treatments given, mortality curve — bring the data, not just the dead birds. If a reportable condition is suspected, your vet and integrator handle agency notification; your job is accurate, dated evidence. Treatment decisions belong with the veterinarian, not this page.
On 30,000 birds, each 1% of mortality is 300 birds — roughly $1,800 of live weight at an example $1.00/lb, plus the feed those birds consumed before dying. Document the cause, the response, and the follow-up in the same log the next audit reads. See the integrator records requirements for why dated mortality entries matter beyond the flock.
The Habit That Catches Causes Early
Log every loss with house, date, and time of day — the same way, every day. A count on paper tells you what died; a timestamped, house-linked record tells you that deaths climbed every afternoon after 2 p.m., or that house two lost birds while house one stayed flat. That is the difference between a number and a clue, and it is what makes the weekly pattern review worth five minutes.
Tracking Mortality in Poultry Log™
Mortality logged in Poultry Log™ is tied to house, flock, and timestamp automatically — so a spike surfaces as a dated change against the flock's own baseline, with the water, feed, and temperature logs on the same timeline to check against. Each flock's mortality history feeds the profitability dashboard, where losses show up as cost per pound produced — the number that decides whether the next flock gets the same program or a different one.
- 2026-10-05: Comprehensive rewrite. Cause-signature table, pattern-over-count framing, five-step spike decision tree, and cost math — replacing the earlier short note.
- Earlier version: brief note on logging mortality patterns.