How extreme heat will harm cattle
Cattle farmers will either have to provide protection for their animals, or shift to more resilient breeds or to other livestock
As a veterinarian involved in climate change-related research, Michelle North was surprised to find an enormous body of research into the effects of climate change on crops all around the world, but that livestock agriculture has been neglected.
“Because livestock contributes to food security, as well as supporting the livelihoods of many people, including poor subsistence farmers, we felt that this gap in the literature and thus policy space needed to be filled,” said North, a climate change researcher at the University of Kwazulu-natal.
She is the lead author of new research recently published in the journal Environmental Research Letters that unpacks the global risk of heat stress to cattle from climate change.
Researchers from the universities of Cape Town, Kwazulu-natal and Chicago analysed today’s heat and humidity conditions around the world, and estimated how they will affect cattle in future decades, depending on different levels of emissions and forms of land use.
They found that more than a billion cows around the world will experience heat stress by the end of the century if carbon emissions are high and environmental protection is low.
This means cattle would face potentially lethal heat stress in much of the world, including Central America, tropical South America, Equatorial Africa, and South and Southeast Asia.
But rapidly reducing greenhouse gas emissions, as well as keeping cattle production close to current levels, would reduce these effects by at least 50% in Asia, 63% in South America and 84% in Africa.
Extreme heat harms cattle in many different ways, particularly when combined with high humidity, they said. It reduces fertility, impairs the growth of calves and can result in increased deaths. It also reduces milk production in dairy cows. All this affects the viability of livestock farming, reducing animal welfare and farm income.
If future carbon emissions are very high, nine in 10 cows will experience 30 or more days of heat stress a year. More than three in 10 will experience it year-round by the end of the century.
Rising temperatures and humidity will force farmers to adapt to these new conditions by, for example, providing ventilation, air conditioning or switching to heat-adapted cattle breeds.
But these measures will become increasingly expensive with future warming. Nor will it be possible in all places, meaning cattle farming might no longer be viable in, for example, India, Brazil, Paraguay, Uruguay and north-eastern Argentina and across the Sahelian and East African countries.
“We’ve seen the deadly impacts for humans of climate change intensifying heatwaves, but the animals that feed us are also at severe risk from heat,” Christopher Trisos, an ecologist and climate change researcher at University of Cape Town, said in a statement.
Expanding cattle production by cutting down or burning tropical forests is unsustainable. “It worsens climate change and will undermine the welfare of hundreds of millions more cattle that will be exposed to severe, year-round heat stress.”
Adapting livestock farming systems to reduce the effects of heat stress will be essential, he said. “Reducing the amount of cattle products in diets can help limit future expansion of cattle farming, creating opportunities to protect and restore forests that can help limit future global warming.”
North said that cattle in most of South Africa already experience about a month of temperatures that exceed their heat stress threshold. This leads to reduced productivity, fertility, health and increased chance of death. But some parts of the country experience several months of heat stress.
“For the most part, temperatures only exceed the heat stress threshold by one or two units — for example, if you start to feel uncomfortably hot at 27°C, these hot days would be, on average, about 28°C. So, in other words, hot, but not extremely so, and for one month or more, every year.”
By the end of the century, however, the average amount by which the heat stress index value exceeds cattle’s threshold for safety or comfort in South Africa will more than double under a low greenhouse gas emissions scenario, and increase five-fold under a higher emissions scenario.
“In addition, there will be more of these hotter hot days: on average around the country, between one to two months more under a lower emissions scenario — so a total of two to four months of these hotter temperatures each year — and more than three to four months more under a high emissions scenario — so, on average six months of very hot days.”
This means that cattle will endure far higher heat stress burdens under climate change, “with high emissions leading to a much higher level of heat stress and its associated impacts”.
North pointed out that climate change-related hazards, including high temperatures, drought, and floods and increasing seasonal variability and unpredictability, make it difficult to farm anything successfully, whether livestock or crops.
“When the seasons are difficult to predict, farmers aren’t able to use hard-earned local or traditional knowledge to know when to plant crops, when there will be the most grazing available for their livestock and therefore when would be best to breed the animals so that the calves have enough food to grow well.”
These changing conditions, too, change diseases and parasites, meaning that farmers will have to be more aware of the health of their animals, and might need to treat them more often. “All of these factors make farming in some areas less viable.”
Intensifying heat will affect smallscale and large commercial cattle farmers. Commercial agriculture will have to implement potentially expensive adaptation mechanisms to ensure their productivity remains high, which means consumers will pay more for products.
This could affect food security, particularly in areas and vulnerable groups who may not be able to afford the increased cost of protein, North said.
Although commercial cattle farmers stand to lose the most income as a result of heat stress, they usually have insurance, good relations with banks and the ability to draw on loans to help them recover from heat-related losses, North said. “This means that large-scale farmers will usually be more able to bounce back after a crisis and be more resilient.”
For small-scale farmers, while the net losses may appear negligible from a larger economic perspective, “these losses can severely affect the farmers’ food security, and can lead to these farmers literally losing their livelihoods and ability to support their families”, North said, explaining how these farmers are far more vulnerable and less able to recover after crises.
To protect their cattle, farmers can provide shade by planting trees or providing areas covered by shade cloth or roofing. For animals kept in barns or sheds, airflow can be increased, fans installed and misters considered. “Some can even consider air conditioning or similar methods of climate control.”
Feeding times can be changed “so that animals aren’t eating and generating metabolic heat during the heat of the day” as can management and handling times “so that you’re not handling, moving, or stressing animals during the heat of the day”. Replacement animals can be selected based on their heat tolerance or farmers can consider moving to breeds known to cope better with heat or to other livestock species.
North emphasised tropical forests must not be cut down by farmers and pastoralists to expand cattle farming, “because that makes climate change much worse and exposes cattle to severe heat risk that can kill them”. And, by reducing the amount of red meat in their diets, consumers will reap health and budget benefits, “as well as reducing demand for meat products and reducing incentives for expanding cattle production”.
For North, the impacts she and her colleagues discuss in their paper “provide yet more justification” that governments need to push for action to reduce climate change, divestment away from fossil fuels and towards renewable energy sources, reduced deforestation and increased protection of natural areas that help buffer the effects of climate change.
“They also need to help their people adapt and be prepared for climate change, through education, through the provision of essential infrastructure, microinsurance or other financial safety nets for farmers and other support systems.”
More government regulation and support services for smallholder farmers and pastoralists is needed to adapt their livelihoods to the changing climate conditions, to support their shift out of livestock farming in the tropics, “or at least supporting or encouraging them to not to cut down forests for grazing or to supplement incomes”.
Heat reduces fertility, impairs the growth of calves and can result in increased deaths. It also reduces milk production