Heat Stress and Rising Mortality in a Broiler Shed
A contract broiler farm in Nagpur houses 5,000 birds in an open-sided shed at 12 birds/m². On day 30, with daytime temperature 38°C and high humidity, daily mortality rises from 8 to 25 birds. Water intake has doubled, feed intake fell 15%, litter is wet and caked, and ammonia is strong. Birds are panting and sitting with wings spread; some have watery droppings. The shed has two 36-inch fans but no foggers, and the water line is a single nipple line with 10 nipples per 1,000 birds. The farm manager wants to start a 5-day antibiotic course and continue until harvest on day 38. The buyer's live-weight price is ₹110/kg, feed conversion has worsened from 1.55 to 1.75, and the average body weight is 1.6 kg.
1. Separate the likely primary causes of the mortality from secondary effects, and justify your priority order.
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Heat stress is the primary cause; the secondary effects are wet litter, ammonia, reduced feed intake and possible opportunistic enteric infection. At 38°C with high humidity, 12 birds/m² and only two fans, birds cannot lose heat. Panting, wing spreading, doubled water intake and a 15% feed drop are classic. Wet litter and ammonia follow from increased water intake and poor ventilation; they further irritate the respiratory tract and reduce performance. Mortality is rising because the heat load is cumulative. Antibiotics address bacteria, not heat, and starting a 5-day course without diagnosis adds cost and resistance risk. The priority order is: reduce heat load and improve air movement; restore water supply and litter quality; then investigate specific disease if mortality continues after cooling.
2. List the immediate actions you would take in the next 24 hours and explain how each addresses the problem.
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Next 24 hours: (1) install foggers/misters and run fans; wet the roof if possible; (2) increase air speed with additional fans and open side curtains fully; (3) check water flow at the far end of each line and add extra drinkers-10 nipples per 1,000 birds is inadequate in heat; (4) provide cool, clean water with electrolytes and vitamin C; (5) remove caked litter and add dry bedding, especially around drinkers; (6) shift feeding to early morning and evening; (7) reduce effective density by moving some birds or partitioning the shed if possible; (8) record mortality twice daily. Each action targets the pathway: cooling lowers heat load; water restores intake; dry litter reduces ammonia; feeding time reduces metabolic heat. Do not start antibiotics until a veterinarian examines sick birds.
3. Should the farm harvest early at day 34 rather than day 38? Support with a simple economic and welfare argument.
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Early harvest is likely better if heat stress continues. At 25 deaths/day, four extra days cost about 100 birds × 1.6 kg × ₹110 = ₹17,600 in dead stock alone. If surviving birds gain only 40 g/day under heat, 4,900 birds × 0.16 kg × ₹110 ≈ ₹86,000 extra revenue; feed for four days at about 120 g/bird/day × 4,900 × ₹32/kg ≈ ₹75,000. The marginal result is roughly negative before labour and medicine. Harvest at day 34 avoids further mortality and poor feed conversion. However, check the buyer's minimum weight and penalty terms; if birds are below contract weight, a partial harvest or thinning may be better. Welfare also favours reducing the heat load or harvesting rather than leaving birds to pant.