Heat Stress Genomic Gains 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
🧬 Your Gains from Genomic Selection
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.
By selecting sires for heat tolerance EBVs, your herd progressively recovers lost production, milk yield, and fertility. Estimated gains after 10 years of consistent selection:
After 5 years
—
gained back / year
After 7 years
—
gained back / year
After 10 years
—
gained back / year
Revenue recovered from reduced milk loss and improved reproductive performance.
Up to
—
per year recoverable with consistent genomic selection
Heat Stress Impact — Current Baseline
THI
—
—
Milk loss / cow / day
—
kg
Total milk lost
—
kg / year
Yield loss
—
% of 305-d prod.
Extra days open
—
repro cost
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.