Short answer: a flock that loses 0–1% of its chicks in the first week, and lands somewhere around 2–4.5% of the birds placed by the time it leaves for slaughter, sits inside the range reported for commercial broiler flocks in large studies. The exact number moves with breed, season and shed management, so the most useful comparison is your own flock against its own past cycles, not a single fixed target.
Broiler mortality rate is the share of chicks placed in a flock that die before reaching market weight, usually tracked as first-week mortality and as cumulative (total) mortality. Every flock loses some birds between placement and pick-up. The real job is knowing how many is normal, which week deserves the closest watching, and the point where a number stops being normal and starts being a warning worth a phone call.
How do you calculate broiler mortality rate?
Divide the number of dead birds by the number of chicks placed, then multiply by 100:
Mortality rate (%) = (birds died ÷ chicks placed) × 100
This gives your broiler mortality percentage for the flock so far.
For example, suppose a flock is placed with 5,000 day-old chicks and has lost 70 birds by day 35. Cumulative mortality is 70 ÷ 5,000 × 100 = 1.4%. Work this out every morning from a running count, not just once at the end of the cycle — the week the losses happened tells you far more than the final total ever will.
What is a normal mortality rate, week by week?
No single public table lists an exact cumulative percentage for every week of a broiler's life, but two sources give real, usable numbers: a review of first-week mortality in Poultry Science, and a large-scale comparison of 4,228 Ross 308 and Hubbard JA787 flocks (64.6 million broilers, Norway, 2015–2021) published in a peer-reviewed mortality-risk study.
| Period | Ideal / target | Average, fast-growing breed (Ross 308) | Average, slower-growing breed (Hubbard JA787) |
|---|---|---|---|
| First week (day 0–7) | 0–1% | 1.40% | 0.76% |
| Week 2 to slaughter | — | 3.05% | 1.49% |
| Total, placement to slaughter | — | 4.41% | 2.24% |
| Dead on arrival at the plant | — | 0.063% | 0.015% |
Two things stand out. First, the ideal first-week figure (0–1%) is lower than what large commercial datasets actually average, so a little above 1% in week one is common and not automatically a crisis by itself — it is the trend across several flocks that matters. Second, breed changes the whole picture: the same study found roughly double the total mortality in the fast-growing Ross 308 compared with the slower-growing Hubbard JA787, raised under the same commercial conditions.
Why does mortality differ so much between breeds?
Fast growth has a cost. The Ross 308 vs Hubbard JA787 study found that chronic conditions such as ascites, growth retardation and hepatitis were more common in the faster-growing breed. Wherever a shed runs a fast-growing broiler, the Ross 308 figures above are the closer comparison point than the slower-growing breed's lower numbers.
What causes most deaths in the first week?
A day-old chick carries a small yolk reserve that is a bridge, not a meal. Chicks that do not find water and feed within the first day or two run out of that reserve and often die on the second or third night. The Poultry Science review also names infections carried from the hatchery, particularly yolk sac infection through a poorly healed navel, as a recognised cause of early deaths, alongside chilling, overheating and culls of weak or lame chicks. Our guide to chicks dying in the brooder walks through the checks to run the same night, and the brooding temperature guide has the week-by-week heat targets.
What causes deaths later in the flock?
Mortality in a well-run flock usually settles down after the first one to two weeks. As birds approach market weight, the Ross 308 vs Hubbard JA787 study points to the same chronic conditions — ascites, growth retardation and hepatitis — becoming more visible in fast-growing birds. Heat stress is also a bigger risk once birds are older, heavier and carrying more body mass through a hot shed; see our guide to summer heat stress for the signs and the fixes.
Your daily mortality record sheet
A single final number tells you almost nothing. A daily record shows you the day things changed. Copy this table onto a sheet in the shed and fill it in every morning before you do anything else:
| Date | Age (days) | Birds alive this morning | Dead today | Cumulative dead | Cumulative mortality % | Notes |
|---|---|---|---|---|---|---|
In the notes column, write down anything unusual that day — a power cut, an unusually hot or cold night, a vaccination, a feed change. Six months of these sheets, kept flock after flock, will tell you more about your own shed than any published benchmark can.
When should you call a vet?
Call when daily deaths stay above your flock's own normal level for more than a day without an obvious cause such as a power cut or an unusually hot day, when the daily count suddenly jumps, or when you see signs of disease: wet or poorly healed navels in young chicks, or swollen bellies, blue combs and birds found dead with no warning in older birds. Describe what you see and share your record sheet with your vet rather than guessing at a cause or starting any medicine on your own.
What does this mean for broiler farms in Pakistan?
Open-sided sheds in Punjab face the two seasons that push mortality hardest in either direction: sharp summer heat and cold winter nights. Our guides to summer heat stress and keeping broilers warm in winter cover the shed changes that matter most in each season. Keep a photo of your daily record sheet on your phone so it travels with you to the dealer or the mill when you need help reading a bad week.
Written by the Vital Feeds editorial team.
How this guide was made: the benchmark figures are taken from a Poultry Science review of first-week mortality and a peer-reviewed study of 4,228 Ross 308 and Hubbard JA787 flocks in Norway, both read in full; the draft was AI-assisted and fact-checked against those sources on 15 October 2026.
Want help reading your flock's numbers? Message the mill on WhatsApp (UAN 0311 1555136) with your record sheet, or see our broiler starter, grower and finisher feed and find your nearest dealer.