Thursday, April 25, 2024

Project aims to determine heat stress limit for sheep

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The new tool will be used to help farmers proactively manage heat stress risks for their animals.
These sheep are been monitored at AgResearch’s Ruakura site to see how they are affected by heat stress, with the work eventually leading to a heat stress index tool for farmers.
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AgResearch scientists are developing a tool to help sheep farmers better predict when their animals are likely to be heat-stressed.

The tool, called a heat load index, will be used to help farmers proactively manage this risk for their animals.

The project, funded by the Ministry for Primary Industries, has scientists monitoring a small mob of Romney ewes in a paddock at its Ruakura site, where the data collected will be used to formulate the index.

The research was outlined at a field day at Ruakura organised by the MPI.

AgResearch scientist Karin Schutz said they are monitoring the ewes’ movements and time spent in shade and grazing pasture. The sheep’s respiration rates are also recorded and counted.

The index – along with a temperature threshold to advise when farmers should start mitigating for heat – should be ready by next summer.

A heat stress risk map will be created using NIWA weather data and sheep population density to show areas where heat stress is potentially an issue.

The work follows similar research where a heat load index was developed for dairy cows and released last year, taking into account temperature, solar radiation, humidity and air movement.

“In general terms, the more humid the weather is, the lower the air temperature is that the animals can cope with,” Schutz said.

That work found that a cow’s respiration rates took off once temperatures hit 21degC.

“If it’s a sunny day without any windspeed or air movement, that’s when cows start to get affected.”

Schutz said that threshold can lift because of external factors such as wind or cloud cover, which can push that temperature to the mid to high 20s.

That index was based on Waikato data during different heat stress trials. This year, more data is being collected from different regions in collaboration with Fonterra and DairyNZ to validate the index and make it more relevant to other regions.

The project had scientists monitor cows using ear tag technology that recorded grazing and ruminating behaviour. Data sensors were also placed on the cattle’s legs to measure lying behaviour. Tail sensors measured skin temperature, and respiration rates were recorded by manual observation.

Schutz said sheep and cows behave in similar ways when facing heat stress.

“They will go and look for shade. If they have plenty of shade, they will sit down in the shade then and go off and graze and go back to the shade again.

“It’s a natural response for animals to go and look for shade.”

Higher respiration rates also increase the need to consume water. If the animals cannot stay cool, their grazing activities are reduced, eventually leading to them breathing hard and panting.

Fonterra’s Mike Shallcrass said New Zealand’s outdoor farming systems are unusual because the animals are farmed all year round and people do not appreciate how odd this is.

Shallcrass said they are often questioned by customers in the marketplace around how outdoor farmed animals are treated when it comes to rain, cold and heat.

“It’s a minority of farmers who get that far in their thinking, but it’s growing. Our understanding of the heat stress mitigations available to farmers is seen as a risk from a business perspective.”

For the past two years, he said, the co-op has created a report for each of its farmers highlighting the estimated production it faces if no mitigations are put in place to stop heat stress.


Watch our latest On Farm Story on time-saving agritech to help farmers manage biosecurity on-farm below

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