Cows make less milk in hot sticky weather

U. WASHINGTON (US) — “Cows are happy in parts of Northern California and not in Florida,” report researchers who studied the effect of climate change on milk production.

Yoram Bauman and colleagues at the University of Washington find that the decline in milk production due to climate change will vary across the US, since there are significant differences in humidity and how much the temperature swings between night and day across the country.

The researchers find that dairy farming is already clustered in the most hospitable areas in the US for cows. (Credit: U. Washington)

The temperature at which cows start producing less milk varies across the country depending on other factors like humidity and overnight temperature swings. (Credit: U. Washington)

For instance, the humidity and hot nights make the Southeast the least friendly place in the country for dairy cows, say the researchers, who presented findings at the Conference on Climate Change.

Their study combined high-resolution climate data and county-level dairy industry data with a method for figuring out how weather affects milk production. The result is a more detailed report than previous studies and includes a county-by-county assessment of the impact climate change will have on Holstein milk production in the US through 2080.

“Using US Department of Agriculture statistics, if you look at milk production in the Southeast versus the Northwest, it’s very different,” says Guillaume Mauger, a postdoctoral researcher in the Climate Impacts Group and co-author of the paper. “It’s reasonable to assume that some of that is due to the inhospitable environment for cows in the Southeast.”

By using detailed climate data covering night and day across the entire country, the researchers made some interesting discoveries. For instance, in Tillamook, Oregon, where the climate is humid and the nighttime temperature doesn’t change much, milk production begins to drop at a much lower temperature than in the dry Arizona climate.

Tillamook cows become less productive starting at around 15 C, or 59 F, while those in Maricopa, Arizona start making less milk at around 25 C, or 77 F. In humid Okeechobee, Florida, cows become less productive at about the same temperature but losses increase at a much faster rate than in Arizona.

Fortunately for cows in Tillamook, however, the temperature there doesn’t stray upward often and so actual milk losses are negligible, the researchers say. In Maricopa, the mean daily losses in summer, when the temperature soars, reach nearly 50 percent.

The authors also found that dairy farmers are already clustering in the most comfortable areas for cows, such as the cool coastal counties of Washington State. But the outlook isn’t good for areas across the southern US where cows are already less productive in the heat of the summer.

“Perhaps most significantly, those regions that are currently experiencing the greatest losses are also the most susceptible: they are projected to be impacted the most by climate change,” the researchers write in the paper.

Still, there’s a notable silver lining in the report. While the researchers project that dairy production averaged across the US will be about 6 percent lower in the 2080s than at the start of the century, other factors are likely to actually boost milk production even more.

“Management practices and breeding are on track to double milk production in Holsteins in the next 30 or 50 years,” Mauger says. “So while a 6 percent drop is not negligible, it’s small compared to other positive influences.”

The research could be valuable to farmers looking to evaluate the cost and effectiveness of methods for keeping cows cool. “You can pick up dairy cows and truck them elsewhere,” says Bauman, who notes that ranchers looking to expand could make decisions based on climate.

The researchers hope next to look at the impact climate has on other barnyard animals, such as pigs, and other effects, such as mortality rate, that rising temperature might have on cows.

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