The first industry-wide thermal index for dairy cattle may be close as exciting research into the issue gains momentum.
PhD student Alice Shirley from the University of Sydney undertook the research and was one of 10 scientists to present her findings at the Dairy Research Foundation Symposium recently, winning the Emerging Scientist competition with her study, 'Hot cows, cool solutions'.
Climate variability across Australia heightens the risk of heat stress in cattle, and most thermal indices used to indicate heat stress are herd-level predictions rather than for individual animals.
Ms Shirley's research aims to develop a water intake model for dairy cattle under varying levels of heat stress.
Water consumption at varying temperatures and volumes can have a sizable, sustained impact on reticuloruminal temperature and, as such, may indicate an individual animal's coping strategies dictated by climatic conditions.
Ms Shirley is exploring existing and acquiring new sensor-derived data to enable the monitoring and management of individual animals fitted with an orally inserted reticuloruminal sensor to identify water intake.
Ms Shirley and her team used a smaXtec Classic Bolus to gather the data.
"Because of where they sit in the rumen, they are impacted by water intake, which was helpful for us," Ms Shirley said.
"This device provides us with key metrics on rumination activity and, importantly, temperature.
"It does this every 10 minutes, 24 hours a day, and an internal memory of six days if required.
"Otherwise, data transfer occurs regularly when the sensors are in contact with the base station that continually reads in cow data.
"This data can then be accessed via an internet browser or throughout the smaXtec app."
Data was acquired from three Victorian pasture-based dairy farms, each running a mixed-breed herd.
The study was carried out on farm A between June 2021 and February 2023 (658 head), farm B between March 2019 and February 2023 (426 head), and farm C between March 2019 and February 2023 (344 head).
Drinking events were identified based on the pattern and magnitude of temperature drop between up to three consecutive observations.
Overall temperature drops and other characteristics of the drinking event were then
calculated, and the developed model was validated on a fourth dairy farm.
Results indicate a peak in the mean (3.87) number of drinks per day across summer compared to winter (2.85).
Average temperature drops due to drinking events were smaller in summer, with farm A recording 4.2 degrees, farm B: 3.6 degrees and farm C: 3.7 degrees, compared to winter, which revealed a drop in temperature of 5.7 degrees on farm A, 5.3 degrees on farm B, and 5.2 degrees on farm C.
Examining the association between the number of drinks per day and a drop in reticuloruminal temperature demonstrated an increase in water consumption per event with a smaller number of drinks.
With the creation of a water threshold model, this preliminary study provides a basis for developing a core body temperature phenotype for the genetic selection of heat-tolerant animals.
"Ultimately, we want to develop a new phenotype for heat stress using these metrics that enable the selection of cattle that are perfectly suited to and most productive in their environment, and this study provides the first step in doing so," Ms Shirley said.
"As this will take time, if we can identify animals that are, or aren't, coping with the heat, we can provide extra cooling technology like fans or sprinklers, additional shade, and change their diet - there are plenty of options, but we need to know which individual animals require the assistance or it may be a financial cost applying changes where they are not needed."
