Heat Stress Loss Calculator
Dairy cattle · Gulf Region & Latin America · Based on peer-reviewed science
🌡 Climate Conditions
Avg. Temperature — Hot Season daily average
°C
Relative Humidity — Hot Season daily average
%
Days/Year in Heat Stress THI ≥ 72
days
🐄 Herd Parameters
Lactating Cows
head
Avg. Daily Yield / Cow 305-d lactation
kg/day
Milk Price per kg
$/kg
Currency
Cooling / Mitigation 0%
No coolingBasic fans + shadeFull cool
Temperature-Humidity Index
Calculated THI
—
—
Milk Loss · Cow · Day
—
kg during heat season
Total Milk Lost
—
kg / year
Yield Loss
—
% of 305-day production
Reproductive Cost
—
extra days open
⚠ Estimated Annual Loss
—
per cow: —
Milk—
Repro—
Saved by cooling—
🧬 Genomic Selection Potential
Based on heritability estimates for heat tolerance (h²≈0.17–0.22) from Ravagnolo & Misztal (2000) and genomic selection accuracy typical for Holstein populations (r≈0.65–0.75). Annual genetic gain reduces the milk loss slope per THI unit by ~2% per year of consistent sire selection. Estimates are cumulative and assume continuous use of top heat-tolerance ranked sires. Actual gain depends on selection intensity, generation interval, and population structure.
Selecting for heat tolerance EBVs reduces the slope of milk loss per THI unit. Estimated annual savings from improved heat-tolerant sire selection:
5 years
—
saved / year of selection
7 years
—
saved / year of selection
10 years
—
saved / year of selection
Scientific Basis & Methodology
THI formula: NRC (1971) livestock weather safety index: THI = (0.8 × Tdb) + (RH/100) × (Tdb − 14.4) + 46.4.
Thresholds: Armstrong (1994); Collier et al. (2012) — high-producing cows (>30 kg/day) show performance decline from THI 68.
Milk loss model: Ravagnolo & Misztal (2000) random regression estimates; West (2003) yield-dependent slope (0.20–0.41 kg/THI unit); Bernabucci et al. (2010) Italian Holstein validation. Loss rate scales with productivity: base 0.20 kg per THI unit for 20 kg/day cows, +0.01 per additional kg of yield.
Reproductive losses: Hansen (2009) conception rate decline (~3%/THI unit above 72); Schüller et al. (2014) days-open model; cost approximated as 50% of daily milk value per extra day open.
Note: Estimates represent potential losses before mitigation and assume a uniform heat stress period. Actual losses depend on breed composition, acclimatisation, management intensity, and facility design.