Global heating could cause an extra 1.2m lamb deaths in Australia each year, study finds

27 03 2024 | 09:28Aston Brown / THE GUARDIAN

University of Adelaide study finds potential lamb deaths from heat stress could increase from 2.1m to 3.3m per year under a 3C rise

Rising temperatures due to global heating will decrease lamb survival and fertility rates in Australia’s sheep flock resulting in industry-wide losses of up to $166m annually, new analysis predicts.

A University of Adelaide study, published in the journal Nature Food, modelled the impact an average temperature increase of 1C and 3C would have on Australia’s $4.3bn sheep industry.

An estimated 2.1 million potential lambs are currently lost annually due to heat stress, the study said. If temperatures were to rise by 3C, that number would rise to 3.3 million.

The report’s lead author, Associate Professor Will van Wettere, said heat stress was a “huge problem that’s only going to get worse”.

“The areas where sheep can be effectively raised in Australia are likely to reduce in the future,” Van Wettere said. “We’re going to have a smaller footprint for agriculture production if things keep going as predicted.

“And it looks like we’ve hit one degree already – it’s a worry, a big worry.”

Van Wettere said sheep in Queensland and arid environments are the most vulnerable to heat stress from rising temperatures, but flocks in cooler climates would still likely experience “significant impacts”.

In two previous Australian studies referenced in the report, heat stress reduced the lambing rate (the number of lambs born per one hundred ewes mated) by 3.5% for each additional day over 32.2C. Extreme heat also decreased a ram’s sperm quality and impaired foetal development.

“When it’s hotter ewes have fewer lambs,” Van Wettere said. “Then there is the effect of heat during pregnancy that results in smaller lambs which are less likely to survive.”

Notably, the report did not model a decrease in the availability and quality of livestock feed and water due to global heating, which would likely exacerbate adverse effects of heat stress.

Australia has the second-highest sheep population in the world, with a national flock of 72 million in 2024, according to estimates by the Australian Bureau of Agricultural and Resource Economics and Sciences. However, like the size of the country’s cattle herd, these figures are based on survey data which some experts say is inaccurate.

The director of the South Australian Drought Hub, Stephen Lee, said feed supplements, selective breeding and more shade cover would allow sheep to adapt to a warming climate.

“Heat stress on sheep production is very significant and predicted to increase,” he said. “But it’s also something we have the agency to address.”

The chief executive of Farmers for Climate Action, Natalie Collard, said the report was a “powerful example” of how global heating is affecting Australian agriculture.

“All of us in the farming sector need to reduce our carbon footprint so we can protect our food supply and the viability of our businesses in the long term,” Collard said.

She said a “serious injection” of research funding was needed to develop more technologies that farmers can use to mitigate extreme weather.

South Australian sheep producer Jane Kellock has increased lambing rates by 30% by feeding her ewes a melatonin-based feed supplement as part of a South Australian Drought Hub trial.

“Research means producers can make an informed decision about how to best adapt to climate change,” she said.

Meat and Livestock Australia said predicting how the livestock industry will be affected by global heating in the long term is difficult, but models were a useful tool to prepare for more extreme weather.

“[This study] allows industry to consider what management practices can be implemented to manage such scenarios should they eventuate,” a spokesperson said.

“Given the size of the country and diverse environmental landscapes, Australia is in a very strong position to maintain a thriving livestock industry.”

Cover photo: Feed supplements, selective breeding and more shade cover would allow sheep to adapt to a warming climate, experts say. Photograph: Simon Scott/The Guardian