The study, led by research scientist Josie Garner, demonstrated the validity of predictions based on DNA testing for heat tolerance in dairy cattle.
Two groups of cows with similar weights, producing similar yields were exposed to the same mild-to-moderate heat event — up to 33C — for four days for a couple of hours in the afternoon, mirroring the fluctuations in temperature and humidity that occurs on a summer day.
Both groups had a reduction in yield, but the cows selected using genomic DNA markers for heat tolerance coped better.
These cows lost 5 per cent less milk yield than the cows that were heat-susceptible, and the heat-susceptible cows recovered slower within the measured two-week period.
During the four-day heat period the heat tolerant cows recorded a 12 per cent decline in milk yield, with the heat susceptible cows reducing milk yield by 18 per cent.
The heat tolerant cows returned to their baseline, the feed intake before the heat challenge — on day six, while the heat-susceptible cows returned on day nine.
Ms Garner said while the heat-tolerant cows were quicker to return to their normal physiological state — the state prior to the heat challenge — neither group returned to the level of production pre-challenge during the two weeks they were monitored.
But results showed the heat tolerant cows were less affected by the heat challenge.
Ms Garner said both groups had the same body temperature — 39C — but the heat-tolerant cows were better at dissipating heat during the heat challenge and averaged half a degree cooler than the heat-susceptible cows.
The heat-tolerant cows got rid of more heat per breath and also more heat through their skin than the heat-susceptible cows.
Validating the heat tolerance for DNA predictions took 18 months, with the initial work to establish the genomic predictions for heat tolerance in dairy combining 11 years of weather station data and milk yield data from more than 366,000 cows as well as genomic data.
An Australian Breeding Value for heat tolerance is under development by scientists at the AgriBio Centre.
Ms Garner, who grew up in the dairy region of Bega, NSW, and now lives on a dairy farm milking cows with her partner, took up the opportunity to complete the study while she was working as a research scientist at Ellinbank.
It was a PhD opportunity and she was “intrigued” by it as it included an in-depth look at physiologies and genetics of cows. Ms Garner also understood the impact heat had on the industry.
Apart from maintaining health and production in a hotter climate, this research has also been considered a win for animal welfare because the cows are bred to be more resilient in hotter conditions.
Ms Garner’s research was recently published in the international science journal Nature-Scientific Reports.
Source: Weekly Times
