Why Broilers Die: The Causes, by Week

TL;DR: Read the timing. Week-one deaths point at the brooder — chilling, overheating, chicks not finding feed or water, piling. Mid-cycle deaths point at disease. Late-cycle deaths point at heat and the growth curve — heat stress, leg weakness, heart failure — and they are the expensive ones, because those birds ate almost all their feed and return nothing. Record deaths daily with dates; the pattern is the diagnosis.

Most broiler loss in the Philippines happens in two windows: the first week and the last.

Week One: The Brooder

Chicks arrive with almost no reserve. Nearly everything that kills them here is environmental.

Cause	What you see	Fix
Chilling	Huddled tight under the heat, loud persistent cheeping	Brooder heat
Overheating	Spread to the walls, panting	Raise the lamp or reduce output
Piling	Chicks heaped in a corner, smothering underneath	Round off corners, fix the draught — act immediately
Not finding feed or water	Empty crops at night, chicks not thriving	Chick feeding schedule — water first, show them
Drowning	In drinkers too deep	Shallow drinkers, or pebbles in them
Poor chick quality on arrival	Weak, wobbly, unhealed navels	Inspect at handover — where to buy day-old chicks

Our chick mortality causes and sick chick symptoms guides cover this window in full. It is the highest-return week of the whole cycle to get right.

Mid-Cycle: Disease

Once brooding is behind you and before the birds get heavy, deaths usually mean an infectious problem.

Coccidiosis — bloody or watery droppings, birds off feed. Litter-borne, which is why floor management and all-in all-out matter.
Gumboro — sharp rise in deaths then a sharp fall, survivors immunosuppressed.
Respiratory disease — CRD, coryza, infectious bronchitis.
Newcastle — nervous signs, green droppings, high mortality.

The response is diagnosis rather than guesswork, and the prevention is a vaccination programme built with a veterinarian or agrivet plus real biosecurity — see chick vaccination schedule and backyard flock biosecurity.

Ammonia from wet litter belongs here too. It damages the airway lining directly and opens the door to everything above — see deep litter system and coop ventilation.

Late Cycle: Heat and the Growth Curve

The expensive window, because these birds have eaten nearly all their feed.

Heat stress is the leading cause in Philippine conditions. A heavily muscled bird generates a lot of metabolic heat and sheds it poorly, and a caged or housed bird cannot walk somewhere cooler. Watch for panting, wings held away from the body, listlessness — see heat stress in chickens.

Deaths at night after a hot day are a specific and common pattern: an uninsulated roof absorbs heat all day and radiates it downward into the evening, so the load peaks after dark.

Structural problems come with the growth curve itself:

Leg weakness and lameness — birds sitting, reluctant to reach feed and water.
Heart and circulatory failure, more likely in heat and at higher weights.

Our Cornish Cross guide explains why these are built into fast broiler genetics rather than being bad luck. The mitigation is largely harvesting on time — see when to harvest a broiler. Holding birds past target increases every one of these risks.

What It Costs You

Losses are not equal.

A chick that dies in week one costs the chick price and a few days of feed.
A bird that dies in the final week has consumed almost its entire feed requirement and returns nothing.

That asymmetry is why late-cycle heat management has such a large effect on the bottom line, and why our feed conversion and is poultry farming profitable guides treat mortality as a cost line rather than an afterthought.

Record It Daily

One line per day: date, number dead, anything you noticed.

That record is what turns “we lost a lot this batch” into a diagnosis:

Front-loaded → brooding.
Middle spike → disease; get a diagnosis.
Back-loaded → heat and weight; check the roof, the airflow, the density and the harvest date.
Steady low trickle throughout → usually density, litter or ongoing parasite pressure.

Keep it with your feed and weight records — see keeping records that are actually useful.

The Honest Limits Here

The causes described and their typical timing are standard broiler production knowledge, and the physiological problems associated with fast growth are documented in poultry science. This guide gives no acceptable mortality percentage, because published figures come from controlled commercial conditions and would be a misleading yardstick for a backyard or small-farm operation — track your own across batches instead. Where deaths are rising or the cause is unclear, get a diagnosis from a veterinarian or your local agriculture office rather than treating on a guess.

Frequently Asked Questions

What causes broiler deaths in the first week?

Brooding problems dominate — chilling, overheating, chicks unable to find feed or water, and piling. Chick quality on arrival matters too, which is why inspecting at handover is worth the minute it takes.

What causes deaths late in the cycle?

Heat stress above all in Philippine conditions, plus the structural problems that come with fast growth — leg weakness and heart and circulatory failure. Heavy birds are the most vulnerable to all three.

How much mortality is normal?

Some loss occurs in every batch, and what matters more than a benchmark is your own figure tracked across batches and the pattern of when the deaths happen.

Why do birds die at night after a hot day?

An uninsulated roof absorbs heat all day and radiates it downward into the evening, so the heat load can peak well after the sun has gone.

Does mortality affect profitability much?

Substantially. A bird that dies late has eaten most of its feed and returns nothing, so late losses cost far more than early ones.

What is the single most effective thing to reduce mortality?

Getting brooding right in the first week and managing heat in the last. Those two windows account for most preventable loss in Philippine broiler growing.

Should I record deaths?

Yes, daily, with the date. The pattern over the cycle is what tells you the cause, and without a record you are left guessing at the end.