DAILY SCIENCE

A vicious cycle of cows, disease, and climate change
Livestock welfare will be key in helping us reign in emissions
October 16, 2020

Sicker livestock produce substantially more methane, a group of researchers has found. What’s more, their new study shows that warming temperatures are also increasing the spread of pathogens and the numbers of unwell livestock around the world.

This highlights a new angle on climate mitigation: while fewer cows are ultimately the better long-term solution for our planet, as livestock numbers inevitably rise to meet growing global appetites, we’re going to have to find better ways, in the meantime, to protect their health—and that of our planet, too.

Farmers are familiar with a whole host of diseases and infections that they have to battle in their livestock. Writing in the journal Trends in Ecology and Evolution, the researchers’ focus was on some of the more widespread ailments among these—such as gastrointestinal worms, and bacterial infections like mastitis—that are also known to increase methane emissions. 

Current estimates suggest that with livestock populations expected to increase by roughly 2.7% annually, that growing population will already cause a 20% leap in methane emissions by 2050. But when the researchers then factored the added effects of a common parasitic gastrointestinal worm into this equation, that figure jumped steeply, to 82%—a fourfold increase in expected emissions. And that was just to illustrate the effects of one type of disease.

There are complex and varied reasons why disease and infection have such severe impacts on emissions. For starters, gastrointestinal worm infections may disrupt the regular makeup of a cow’s gut microbiome, directly resulting in the production of more methane. But illness can also have more indirect effects by weakening animals, making them less productive, and causing them to grow more slowly. That means they take longer to reach farmers’ targets for dairy production, or weight gain for meat. 

Often, this pushes farmers to keep animals around for longer in order to meet their targets, which consequently increases the amount of methane livestock pump out over the course of a lifetime. Alternatively, farmers might compensate for low productivity by increasing the numbers in their herd, which naturally drives more emissions.

The methane cost of illness in livestock is a trend that’s increasingly showing up in the literature—some of which the researchers on the current used to make their estimates. For instance, studies show that lambs infected with gastrointestinal worms produced 33% more methane per kilogram of feed, compared to uninfected lambs. Also in sheep, disease-related weight loss in females leads to slower milk production—resulting in an 11% increase in the methane emissions per kilogram of weight gain in their lambs, because with less milk, they take longer to grow. Meanwhile in cows mastitis, which affects udders and can slow milk production, causes an 8% increase in methane per kilogram of milk—because cows take longer to hit the farmers’ dairy-production targets. 

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These early studies underscore the fact that animal welfare is a key player in agricultural emissions, and that it deserves more attention. And to complicate this picture further, rising temperatures are increasing the prevalence of many diseases that plague livestock, because the warmth accelerates their breeding. What’s more, antibiotic resistance in some bacteria—like those that cause mastitis—is also growing under hotter conditions, making disease control a trickier pursuit.

To start addressing this challenge, we have to begin by more fully investigating the role of disease in enhancing emissions, which is currently so under-appreciated as a player in livestock’s planet-altering effects, the researchers say. Building on that, we need to develop more inclusive climate models that reflect these additional emissions, to give us a much more realistic picture of global climate.

We’ll also need to find new, creative ways to treat and reduce disease, to lessen the load on animals and the planet, and to free livestock from this destructive climate-and-disease feedback loop. As for consumers—the study’s revelations add significant weight to the argument for reducing our intake of dairy and meat (if that’s a dietary option). 

Ultimately, making these long-term changes will come down to our ability to tie the welfare of the animals in our charge, to the climate changes that affect us all. 

Source: Ezenwa, et. al. “Infectious Diseases, Livestock, and Climate: A Vicious Cycle?Trends in Ecology and Evolution. 2020

Image: Pixabay

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