HERFS/AUTUMN BONUS TYDSKRIF 2026

Do not let heat stress sabotage your dairy herd! Stephan van der Westhuizen – Technical Specialist: Dairy Every dairy farmer knows that cows do not just survive on feed alone, they thrive when their environment supports their wellbeing. But as climate patterns shift and summer temperatures in South Africa regularly exceed 30°C, heat stress has quietly become one of themost destructive threats to dairy operations. It doesn’t arrive like a disease or an obvious disaster, but its effect is undeniable and experienced in lower milk yields, poor conception rates, and long-termdamage to herd health. The question is not whether heat stress exists, but how to stop it from sabotaging your herd. When heat stress sets in, cows eat less, their metabolic function slows down, and milk production can fall drastically, by up to 40% in severe cases. Fertility also suffers, with conception rates dropping by 20–30%. At the same time, cows become more vulnerable to disorders like ruminal acidosis, mastitis, and lameness. Managing this threat starts with vigilance and the right tools. One such tool is the Temperature-Humidity Index (THI), which gives early warning of heat stress risk. Mild stress begins at a THI of 68, while levels above 74 signal severe danger. Graph 1 illustrates this dramatic increase in the respiration rate as THI rises. These risks are not theoretical. Research shows that cows exposed to high THI conditions can exceed 70 breaths per minute – nearly double the normal rate of 30 to 40 breaths, which means their bodies are struggling to cool down. Graph 1: THI vs Cow Respiration Rate Every dairy farmer knows that cows do not just survive on feed alone, they thrive when their environment supports their wellbeing. But as climate patterns shift and summer temperatures in South Africa regularly exceed 30°C, heat stress has quietly become one of the most destructive threats to dairy operations. It doesn’t arrive like a disease or an obviou disaster, but its ffect is undeniable and experienced in lower milk yields, poor conception rates, and long-term damage to herd health. The question is not whether heat stress exists, but how to stop it from sabotaging your herd When heat stress sets in, cows eat less, their metabolic function slows down, and milk production can fall drastically, by up to 40% in severe cases. Fertility also suffers, with conception rates dropping by 20–30%. At the same time, cows become more vulnerable to disorders like ruminal cidosis, m stitis, and lameness. Managing this thr at starts with vigilanc and the right tools. One such tool is t T mperature-Humidity Index (THI), hich give early warning of he t stre s risk. M ld stress begins at a THI f 68, while levels above 74 signal severe danger. Graph 1 illustrates this d amatic increase in respiration rate as THI ris s. Th se risks are not the retical. Research shows that cows exposed to high THI conditions can exceed 70 breaths per minute, nearly double the normal rate of 30 to 40 breaths , which means their bodies are struggling to cool down. Do not let heat stress sabotage your dairy herd! Stephan van d r Westhuizen - Technical Specialist Dairy Gr : THI ver us cow r i rate THI (Temperature-Humidity-Index)