Livestock Temperature Stress Calculator

Which numbers are official, and which are not. The THI formula — THI = (0.8 × T) + [(RH/100) × (T − 14.4)] + 46.4 — is the one AHDB publishes (Mader et al., 2006). AHDB puts the onset of dairy heat stress at THI around 68, restated in July 2026, and notes high-yielding cows can show stress below it. The higher bands used here for moderate and severe risk, and the beef, sheep and pig thresholds, are conventional working values from the wider literature — AHDB publishes no banded scale, so treat those steps as a gradient, not a rule. Poultry figures are different: those come from statutory DEFRA codes and are quoted as written.

Disclaimer: recommendations follow official UK guidance. Cattle, sheep and pigs: AHDB and NADIS. Poultry: DEFRA Code of Practice for the Welfare of Laying Hens and Pullets, Code of Practice for the Welfare of Meat Chickens, and PB 10543 Heat Stress in Poultry. Individual animal responses vary by breed, age, condition, acclimatisation and housing. Housed poultry welfare depends primarily on in-house management; outdoor ambient temperature is a guide to ventilation load, not a direct indicator of bird body temperature. Always monitor animals directly and consult your veterinarian if concerned.