Commercial broiler genetics from Cobb-Vantress and Aviagen are capable of reaching 4.5–6.5 lb (2.0–2.9 kg) in 5–7 weeks under ideal conditions. But "ideal" on paper and "ideal" in your house rarely match. Use this chart to track your flock against breeder targets, spot drift early, and take action before margin disappears.
Cobb 500 Growth Chart (2022 Performance & Nutrition Supplement)
Source: Cobb-Vantress, Cobb500 Broiler Performance and Nutrition Supplement (2022). Targets are for mixed-sex birds under standard management conditions.
| Age | Live Weight | Live Weight | Weekly Gain | Cumulative FCR |
|---|---|---|---|---|
| 1 day | 42 g | 0.09 lb | — | 0.80 |
| 7 days | 190 g | 0.42 lb | 148 g | 0.88 |
| 14 days | 470 g | 1.04 lb | 280 g | 1.10 |
| 21 days | 975 g | 2.15 lb | 505 g | 1.24 |
| 28 days | 1,620 g | 3.57 lb | 645 g | 1.34 |
| 35 days | 2,190 g | 4.83 lb | 570 g | 1.53 |
| 42 days | 2,910 g | 6.41 lb | 720 g | 1.69 |
| 49 days | 3,300 g | 7.26 lb | 390 g | 1.80 |
Ross 308 Growth Chart (2022 Performance Objectives)
Source: Aviagen, Ross 308 Broiler Performance Objectives (2022). Targets are for mixed-sex birds under standard management conditions.
| Age | Live Weight | Live Weight | Weekly Gain | Cumulative FCR |
|---|---|---|---|---|
| 1 day | 42 g | 0.09 lb | — | 0.80 |
| 7 days | 190 g | 0.42 lb | 148 g | 0.88 |
| 14 days | 485 g | 1.07 lb | 295 g | 1.10 |
| 21 days | 940 g | 2.07 lb | 455 g | 1.24 |
| 28 days | 1,540 g | 3.40 lb | 600 g | 1.34 |
| 35 days | 2,230 g | 4.92 lb | 690 g | 1.50 |
| 42 days | 2,950 g | 6.50 lb | 720 g | 1.65 |
| 49 days | 3,350 g | 7.39 lb | 400 g | 1.78 |
- Cobb-Vantress. Cobb500 Broiler Performance and Nutrition Supplement (2022). Download PDF
- Aviagen. Ross 308 Broiler Performance Objectives (2022). aviagen.com
- Poultria. Cobb 500 Broiler Management Guide. poultria.com
Choosing Your Reference Strain
Most commercial flocks use either Cobb 500 or Ross 308. The two look similar but differ in key ways:
| Trait | Cobb 500 | Ross 308 |
|---|---|---|
| Day 14 weight | 470 g | 485 g |
| Day 35 weight | 2,190 g | 2,230 g |
| FCR to 2.2 kg | 1.48–1.54 | 1.45–1.50 |
| Breast meat yield | 23.5–25.0% | 22.5–24.0% |
| Heat tolerance | High | Moderate |
If you don't know which strain you're growing, check your placement records or ask your integrator. The difference in growth rate is small in the first 2 weeks but becomes more pronounced by week 4–5.
When Weights Fall Below Target: Decision Tree
Seeing birds below target weight? Work through these checks in order before the problem compounds.
Weigh at least 30–50 birds per house, randomly selected. Catch birds when crops are empty (mid-morning is ideal). Check that your scale is calibrated. If your method is flawed, the "problem" may be measurement error.
Are feeders and drinkers accessible to all birds? Is feed fresh and not damp? Verify that the delivered feed matches the ration schedule for the correct phase (starter, grower, finisher). Track daily feed consumption per bird against expected intake from the growth chart.
Brooder temperature should be 32–34°C (90–93°F) at floor level in week 1, dropping ~3°C per week. Heat stress (house too hot) is the #1 reason for reduced feed intake after week 3. Check ventilation, evaporative cooling, and litter condition.
Morbidity or elevated mortality (>1% per week after day 7) directly reduces flock weight. Look for signs of respiratory distress, lameness, or uneven cloacal tones. Call your veterinarian if you see patterns.
If the deviation is >10% below target by day 21, calculate the projected revenue impact. Extend grow-out by 1–2 days only if FCR remains acceptable. Adjust your budget forecast accordingly — the earlier you know, the more you can adapt.
How to Sample Broiler Weights
Consistent, accurate sampling is the foundation of growth tracking. Here's the protocol:
- Select a random sample: At least 30–50 birds per house, or 1–2% of the flock if larger. Do not pick visibly sick or cull birds.
- Time it right: Weigh mid-morning, after the crop has emptied overnight but before afternoon feed allocation fills it.
- Weigh individually: Use a hanging gram scale or a certified digital platform. Record each bird's weight.
- Calculate: Average weight, standard deviation, and coefficient of variation (CV%).
- Compare: Against the breeder targets above for the same age. Adjust for your specific strain.
- Log it: Record the date, house number, average weight, and CV% in your flock record system.
Uniformity matters as much as the average. A flock with a CV% above 10% at day 21 is likely to have uneven feed access, health issues, or management discrepancies that should be investigated.
FCR Benchmarks by Age
Feed Conversion Ratio (FCR) measures how many pounds of feed it takes to produce one pound of live weight gain. Lower is better:
| Breed | Day 21–28 FCR | Day 35 FCR | Day 42 FCR | Day 42 Market FCR | Assessment |
|---|---|---|---|---|---|
| Cobb 500 | 1.25–1.30 | 1.50–1.55 | 1.65–1.70 | 1.53–1.69 | Excellent: ≤ 1.55 | Good: 1.55–1.70 | Needs work: > 1.75 |
| Ross 308 | 1.25–1.30 | 1.48–1.52 | 1.63–1.68 | 1.50–1.65 | Excellent: ≤ 1.50 | Good: 1.50–1.65 | Needs work: > 1.70 |
FCR rises sharply after 42 days. Most growers hit market weight at 42–49 days. Extending beyond 49 days typically increases FCR faster than it increases sale weight — use the FCR guide to decide when to catch.
Tracking Growth in Poultry Log
When you record house entry/exit counts, sample weights, feed deliveries, and mortality in Poultry Log, the system compares your flock's actual growth against the target curve for your breed. If growth drops below the 10% threshold, you get an alert with suggested checks.
Each flock's final performance feeds into the profitability dashboard, where you can see how growth rate and FCR affected margin. The settlement calculator lets you verify your independent numbers against your integrator's sheet, and the budget template helps you plan feed purchases and forecast revenue based on projected weights.
- 2026-09-03: Separated Cobb 500 and Ross 308 tables with direct breeder citations. Added decision tree and sampling protocol. Added FCR benchmarks and contextual links.
- 2024-01: Initial version.