Heat stress is the fastest way to lose money in a broiler house, and it is almost always visible before it is fatal — if you are watching the right signal. Birds begin panting around 86°F (30°C) at bird level, and sustained temperatures above 95°F (35°F) turn a performance problem into a mortality event within hours. The earliest reliable signal is not panting: it is water. Water intake rises roughly 2–3% for every °F above 70°F, hours before birds visibly suffer. This page covers the temperature response bands, the water-signal protocol, and the prevention stack that keeps birds inside their comfort zone when the weather does not cooperate.
What Happens at Each Temperature Band?
| Bird-Level Temperature | What the Birds Do | What You Do |
|---|---|---|
| Below 75°F (24°C) | Comfort zone — normal intake, normal gain | Standard program; watch for cold stress in winter instead |
| 75–85°F (24–29°C) | Intake starts shifting — birds drink more per pound gained, eat slightly less | Verify cooling pads wet properly, tunnel shutters seal, drinker pressure is right |
| 86–90°F (30–32°C) | Panting begins; feed intake drops noticeably; birds spread from feeders and seek shade/air | Act now: full tunnel, pads wet, lights dimmed per label, check every fan runs at speed |
| Above 95°F (35°C) | Panting heavy, wings lifted, mortality risk rising sharply — fast-growing birds suffer first | Emergency protocol per your veterinarian and integrator: fogging/dousing per product labels, maximum ventilation, heat-emergency lighting practices, prepare for possible early catch |
The Water Signal: Catching Heat Before the Birds Show It
Water is the early-warning metric because birds drink to cool themselves — and they start doing it before they stop eating or start panting visibly. The protocol:
- Read meters at the same time daily and compare against the water consumption chart for the age and the day's temperature. At a comfortable 70°F, a week-6 Cobb 500 bird drinks about 357 mL/day — expect roughly a quarter more at 80°F and half again at 90°F.
- A noon spike against your own baseline — not against the chart alone — is the flag. A house running 20% above its usual intake on a hot afternoon is telling you its cooling system is not keeping up.
- Pair water with feed: water up + feed down on a hot afternoon = heat load. Water down + feed down = drinker problem or disease — a different emergency entirely. See the water early-warning guide.
The Prevention Stack: What Keeps Birds in the Zone
- Ventilation capacity verified before summer, not during it. Every fan runs at full speed, shutters seal, pads wet completely and evenly, static pressure holds. A single dead fan in week 5 of a July flock is a margin event.
- Know your house's hot spots. Walk the floor with a thermometer at bird level in mid-afternoon — corners, the end farthest from the controllers, the row under a failed pad. Cool the worst point, not the sensor.
- Feed timing: birds eat less in the heat, so shift feeding effort toward cooler hours where your program allows — more feed in the morning and evening, less during the afternoon peak. Intake is what you can still influence when temperature is not.
- Litter and air quality: wet litter from over-drinking or leaking drinkers adds humidity, which makes effective temperature higher than the thermometer says. Dry litter is heat-stress armor — see the litter ammonia guide.
- Weeks 4–6 are the danger window: fast-growing birds generate the most metabolic heat. The ADG chart shows this is also when gain matters most — a heat slump in week 5 costs the most weight because it happens when the bird is worth the most per pound gained.
When Heat Hits Anyway: Decision Tree
Controller reads one point. Walk the floor with a thermometer. If the hottest zone is 8°F above the sensor reading, the sensor is not your emergency — the hot zone is.
Fans at full speed (listen and feel), pads wet across the full surface, shutters sealing, pumps running. Most heat emergencies are equipment failures discovered late, not weather surprises.
Pull the last 48 hours of water per bird against the chart and feed intake against the feed chart. The size of the deviation tells you how long the house has been heat-loaded and how much performance is already lost.
Follow your veterinarian's and integrator's heat-emergency guidance. Then project: a week-5 flock that eats 10% light for three days loses roughly 50 g per bird of gain — about 3,300 lb across 30,000 birds. Compare that to the cost of the extra cooling you skipped in May.
Tracking Heat and Water in Poultry Log™
Water logs with time-of-day stamps, temperature context, and house-level comparison are what make the water signal usable — a noon spike shows as a dated deviation against the flock's own curve, not a number you reconstruct from memory. When heat events and mortality land on the same timeline as water and feed, the cause review that follows is a five-minute read instead of an argument. And the profitability dashboard shows what each heat event actually cost per pound — the number that justifies next year's cooling budget.
- 2026-10-05: Comprehensive rewrite. Temperature response bands, water-signal protocol, prevention stack, and emergency decision tree — replacing the earlier short note.
- Earlier version: brief note on the noon water spike.