US research points to lower milk yield from cows exposed to wildfire smoke

A team at the University of Oregon has begun a three-year study looking at the effects of air quality and other stress factors on dairy cattle

Juliana Ranches drove to work in eastern Oregon in early September through wildfire smoke so thick that, for a moment, she thought it was just a grey, foggy day and it would soon start to rain.

Ranches is a livestock researcher relatively new to living in the area, and the conditions were unlike anything she had experienced before, leading her to ask questions about the animals that spend their summers in the smoke. Eastern Oregon has this year experienced regular wildfires since early July.

We know there is a negative effect," Ranches said, referring to the cows grazing outside in some of the most polluted air in the US. The area registered 160 on the air quality index (AQI) in early September after reports of a large number of wildfires, a level that can put human health at risk.

There is a little bit of work out of California with [dairy and beef] producers and indirect impacts, reporting lower conception rates and birthrates, but we cannot say for sure because there are no studies in a controlled environment looking into that."

Research into the impact on livestock bred for human consumption is limited, although it is known that particulate matter from the smoke is a significant health threat, especially when exposure is long-term.

According to new preliminary research from the University of Idaho, a sample of dairy cattle exposed to poor air quality and heat stress produced less milk - about 1.3 litres less than normal (just over two UK pints) - a day than average. Some cows had not fully recovered two weeks after the air quality improved. But because this observation was based on just one herd, the data does not yet translate into solid recommendations for ranchers and farmers. The work must be scaled up to explore larger patterns.

It is why Ranches, along with her colleague Jenifer Cruickshank, who specialises in dairy management, has begun a three-year study to collect more data on cows and the effects of wildfire and smoke, as part of which they have put nearly 30 cows out to pasture.

I call them my smoke cows," said Cruickshank. During a wildfire event that results in an AQI measure over 50, she takes daily milk samples and blood tests, which will be analysed as stress markers. The cows' respiratory rate and body temperatures are also documented.

We're getting a finer-grained picture of what these cows are experiencing, through poor air quality associated with wildfires - a better understanding of the physiological effects on them, like is it mild? Is it severe? Is there diversity among the response in the cows? With that information, we can start to look at the negative effects and minimise the damage," she said.