Heat stress has a detrimental impact on the health of dairy cows, milk composition and production and can also have negative effects on forage nutritional composition and yield.
DairyBio and DairyFeedbase - joint ventures of Dairy Australia, Agriculture Victoria and the Gardiner Foundation - are actively developing innovation and technologies for farmers to reduce these impacts.
The temperature humidity index (THI) accounts for the combined effects of environmental temperature and relative humidity and is a useful way to assess the risk of heat stress.
The THI indicates the level of heat stress for a day, but it does not measure the accumulation of heat due to sustained or repeated heat events.
This makes it difficult to assess the total stress of a heatwave lasting multiple days.
Heat stress affects milk production by significantly reducing the cow's dry matter intake.
There are other effects not so evident, for example, heat stress increases subclinical ketosis, decreases reproductive performance, and can compromise mammary gland development.
The DairyFeedbase Feeding Cool Cows project team's early results show that incorporating a fat supplement into the diet of dairy cows during summer can mitigate some of these effects on milk production.
They also found that feeding betaine can reduce a cow's body temperature, which raises questions about mechanisms to maintain feed intake and milk production during long and hot summers.
The team is now actively recruiting partner farms from all over Australia to help assess the effect of heat events on-farm for a range of production systems and environments to then devise and test strategies to reduce these impacts.
- Reducing negative effects of heat stress
- Do not forget dry cows in hot conditions
- Northern Victorian dairy farmers safeguard herd welfare during summer
"We know that up to half the reduction in milk production from cows during heat events can be due to reduced feed intake," Feeding Cool Cows project leader and Agriculture Victoria senior research scientist Dr Leah Marett said.
"The Feeding Cool Cows project is developing strategies to offset this reduction by identifying dietary ingredients that help cows maintain intake or offset the effect of reduced intake on milk production.
"We need Partner Farms to help improve our understanding of the impact of the severity and duration of hot weather on commercial farms.
"And in turn, we will support farmers to explore how hot weather, nutrition, management and genetics contribute to the productivity of their herd."
Heat tolerance ABV
As part of the DairyBio animal program, Agriculture Victoria research scientists together with DataGene developed and released the world's first Heat Tolerance ABV in December 2017.
"Heat stress is an important factor that influences productivity and health in dairy cows, and the climate change modelling conducted by Agriculture Victoria shows us this is going to become an even bigger challenge," DairyBio animal program leader, Agriculture Victoria principal research scientist and La Trobe University Professor Jennie Pryce said.
"Selecting bulls using the Heat Tolerance ABV in the DataGene Good Bulls Guide and app is an important step in a heat mitigation strategy.
"The Feeding Cool Cows project will be helping to collect data which will help validate and improve the reliability of the ABV."
The proposed DairyBio 2021-26 (DairyBio21-26) animal program projects have a key focus of adapting to climate change through expanding the genomic prediction of heat tolerance to integrate data from wearable sensor devices and the development of breeding values to reduce the environmental impact of dairying.
Heat does not just affect dairy cows; it also has a substantial effect on forage.
"The climate modelling that we have completed, combined with the messages industry are providing have defined the targets for the next DairyBio forage program," DairyBio forage program leader and Agriculture Victoria senior research scientist Dr Noel Cogan said.
"The future work will take the delivered technology in genetic improvement and F1 hybrid breeding that is in the process of commercialisation in perennial ryegrass and fast track the application in the warm season and short term grasses.
"Extensive testing of the F1 hybrid breeding is ongoing and demonstration trials have been planted at AVR Hamilton, while commercialisation and seed multiplication is progressing and aiming for a 2025 commercial release."
The DairyFeedbase Pasture Smarts team are also actively recruiting partner farms to help further refine the Pasture Smarts product prototype and app rollout.
Pasture analysis tool
This game-change pasture analysis tool can also assist with managing heat events.
"The Pasture Smarts app will deliver to farmers an easy to understand measurement of pasture performance and utilisation right to their phone," Pasture Smarts project leader and Agriculture Victoria senior research scientist Dr Elizabeth Morse-McNabb said.
"Knowing the amount of pasture you have is the first step for better utilisation of a farmer's most important resource, in future stages, we will be incorporating nutritive assessments which will assist farmers to ensure that their cows are getting not only the right amount of forage but also of the right quality they require to maintain production."}
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