It takes just one sweltering day to reduce a dairy cow’s milk production by up to 10% – and that single day of heat stress can still affect output more than 10 days later. Even high-tech cooling systems often aren’t enough to counter the effects.
By Lucille Botha, senior journalist at African Farming and Landbouweekblad
A large-scale study of 130 000 dairy cows from about 300 farms in Israel – published in the journal Science Advances – highlights how rising temperatures could impact milk production by mid-century.
When wet-bulb temperatures (which combine heat and humidity to reflect how hot it feels) rise above 26°C on hot, humid days, milk production can drop by up to 10%.
“When cows are exposed to these muggy conditions, often called steam bath conditions, it takes more than 10 days for milk production to bounce back to normal levels,” the researchers report.
Cows in high-production phases – due to lactation stage or the number of calves they have had – are especially vulnerable to heat stress. The decrease in milk output due to heat stress is more than twice as high for cows that have had two or more calves, the study found.
Cooling Helps, But Not Enough
Almost all the farms studied had shade structures in place and used systems such as fans, sprinklers or evapotranspiration methods to cool the cows and their surroundings.
The research shows these measures could only offset about half of the milk losses on a 20°C day. At 24°C, they reduce losses by only about 40%.
The hotter it gets, the less these measures help – but installing cooling systems is still worthwhile, the researchers note.
Their cost analysis found that the investment in cooling equipment typically pays for itself within 18 months, based on the annual value of milk losses avoided.
Farms in countries that already experience high summer temperatures benefit the most from such cooling technologies.
Even technologically advanced farms may not be fully prepared for climate change, says Eyal Frank, assistant professor at the University of Chicago Harris School of Public Policy. He and his team found that without any cooling systems, the top 10 milk-producing countries in the world could see milk production fall by about 4% per day. With cooling systems, that drop could be limited to between 1,5% and 2,7% in the five largest producers: India, Pakistan, Brazil, the United States and China.
Also read: Combating heat stress in dairy cows: New findings and future directions
More Heatwaves Require New Plans
Fanie Ferreira, CEO of the Milk Producers’ Organisation (MPO), says the research highlights the urgent need for proactive adaptation – whether through infrastructure upgrades, genetic selection for heat tolerance, or improved management practices.
“The data in the study can also help model the economic impact of climate change on dairies more precisely, which is valuable for long-term planning and policy,” he notes.
Ferreira believes, however, that more research is needed to understand the effects of prolonged high temperatures, which are becoming increasingly common in South Africa. He says KwaZulu-Natal and the Eastern Cape – two key milk-producing regions – are facing increasingly longer periods of heat and humidity. This not only reduces milk yields but also affects animal health, fertility and nutrition. In many cases, it impacts herd performance across seasons.
The Western Cape is also under pressure due to rising average temperatures, more frequent heatwaves and persistent drought. These conditions are making both water and grazing increasingly scarce. Ferreira expects areas such as the Breede River Valley and parts of the Overberg to be among the hardest hit.
“Climate shifts can threaten the viability of certain production areas, particularly in terms of water availability, high temperatures and increasing production costs. Dairy farming is extremely capital-intensive, so moving a production unit to another region is not a simple option. It is more realistic that producers will need to adapt their existing systems to cope with a changing climate.”
He adds that cooling systems such as fans, sprinklers, misting equipment and shade structures are already common on farms in warmer, wetter areas like KwaZulu-Natal and parts of the Eastern Cape.
These systems are also being adopted more widely in northern production areas such as Gauteng, Limpopo and Mpumalanga.
But as heatwaves become more frequent and intense, even current systems may not be enough.
Cooling infrastructure also depends on reliable access to water and electricity, something that cannot always be guaranteed in South Africa.
“Farmers will increasingly need to integrate smart cooling solutions into their existing infrastructure to protect herd health, milk production and fertility,” Ferreira says. “These adaptations could, however, significantly affect the cost structure of a dairy farm – and margins are already under pressure.”
Farmers Are Having to Make Their Own Plans
Ferreira says there is currently no integrated, long-term national strategy focused specifically on climate change and the dairy industry, but various role players – including the MPO – are working to consolidate and share knowledge, research and best practices.
“Producers often find their own solutions, without notable government or policy support, and that comes at a cost,” Ferreira says. “Farmers must adapt not only to safeguard their production, but also to meet sustainability requirements in order to have access to markets and finance.”
He says some dairy farmers have started to specifically select animals with greater heat tolerance without compromising on milk production. They are, for instance, crossbreeding high-yielding breeds such as Holstein with others that are better adapted to hotter conditions.
Producers are also reassessing the design of their milking and feeding stalls and resting areas to improve air flow, provide natural shade and allow for better temperature control. This includes choosing roofing, flooring and partition materials with heat management in mind. Moveable or modular structures are also being used for greater flexibility.
Another strategy involves adjusting feed plans to reduce cows’ internal heat production – for example, by offering more easily digestible feed during warmer months. Many farmers are also shifting milking times to the cooler parts of the day, and closely monitoring cows’ behaviour and body temperature. Water management and maintaining electrolyte balance during periods of heat stress are also becoming key focus areas.
