Tim McAllister knows hundreds of scientists, possibly thousands. That’s because he’s the principal research scientist for ruminant nutrition and microbiology with Agriculture Canada in Lethbridge and an adjunct professor at six Canadian universities and universities in China and India.
McAllister, who grew up on a farm near Innisfail, Alta., has authored or co-authored 660 peer-reviewed scientific papers on topics such as antimicrobial resistance and the sustainability of livestock production.
He is also chair of a United Nations steering committee studying livestock and the global impact on the environment.
So over the years, McAllister has had thousands of conversations with fellow scientists about livestock. However, in all those conversations, one topic rarely came up — glyphosate’s impact on the gut health of cattle, sheep, pigs and poultry.
“I haven’t heard serious discussion around that, at all,” McAllister said from his Lethbridge home office in the middle of April.
“I do a lot of work on antimicrobial resistance. We don’t really view glyphosate as a serious antibiotic…. It’s (in) a different category.”
McAllister’s perception of glyphosate is much different than the mulititude of ordinary people on Twitter and Facebook.
Millions seem convinced that glyphosate, the active ingredient in Roundup and the dominant herbicide in the world, is a threat to the beneficial micro-organisms in the guts of livestock and humans. Social media influencers, dietitians and others have strident opinions on glyphosate residues, gut health and the microbiome.
The microbiome is the genetic material of all the microbes — bacteria, fungi, protozoa and viruses —that live on and inside an animal.
One such person is Dr. Zach Bush, whose website describes him as an “internationally recognized educator on the microbiome as it relates to our health, disease and our food production systems.”
“(Glyphosate) acts as an antibiotic to kill the microbial diversity in your intestines. We now know (this) is the beginning of chronic disease. Many chronic diseases are now being mapped back to injuries in the microbiome,” Bush told Salon.com.
“As we wipe out the bacteria and fungi with this broad-spectrum antibiotic in our food, we are killing the health of our animals, the livestock we consume, beef, poultry, pork, and everything else. So, we’re making those animals sick.”
A Canadian veterinarian has shared a similar theory.
Dr. Ted Dupmeier, who operates a practice at Shaunavon, Sask., has said that glyphosate residues are harmful for cattle.
“The other thing that really started to make me think about it as a veterinarian is, ‘boy, I see a lot of clostridial problems,’ ” he told The Western Producer in 2017.
“When we have glyphosate in there, we’ll see the clostridial bugs go up even in vaccinated herds.”
Clostridial diseases include things such as blackleg and tetanus, and such health issues are resolved when animals are fed rations without glyphosate residues, Dupmeier said.
Lab studies vs. the real world
Some studies do support Dupmeier’s theory.
In 2013, German researchers published a paper in Current Microbiology, asking if glyphosate harms bacteria in the guts of poultry. They concluded that harmful bacteria such as salmonella and clostridium are resistant to glyphosate. Meanwhile, glyphosate damaged some of the healthy bacteria in the gut.
“A reduction of beneficial bacteria … by ingestion of glyphosate could disturb the normal gut bacterial community,” the scientists said.
Therefore, the population of gut bacteria could be thrown out of balance, allowing disease causing bugs to thrive.
However, this study and similar research on glyphosate was done using a method called in-vitro.
The bacteria were grown in a lab and dosed with glyphosate.
Many toxicologists are skeptical about in-vitro studies because the dose is usually much higher than real world exposure. As well, a test tube experiment cannot replicate what happens inside the guts of a cow, pig or chicken.
The European Food Safety Authority (EFSA), which is responsible for risk assessment of pesticides, has studied the question of glyphosate and livestock health.
A team of German scientists reviewed the data and concluded that glyphosate residues are not a health hazard for livestock.
“Considering the results of the toxicological studies on different species and in particular the absence of adverse effect in dairy cows fed during 28 days with a diet containing 400 p.p.m. of glyphosate, glyphosate is not expected to have, even at the maximum dietary burden, effects on the microbial communities in the rumen impacting on the health of bovine and ovine species,” the EFSA said in a 22-page report published in 2018.
Bayer, which manufactures Roundup, cited the EFSA report and mentioned a company study on the same issue.
“Bayer researchers recently published (an article) in the Journal of Animal Science and concluded that the weight of the evidence suggests that glyphosate use in crops fed to poultry and livestock has not affected animal health, rumen/gut microbes or production.”
Meanwhile, researchers at Aarhus University in Denmark have been studying glyphosate residues and the health of poultry and pigs. The study concludes this summer, but the lead scientist, Martin Tang Sorensen, didn’t respond to an interview request.
McAllister hasn’t heard of similar studies in North America, possibly because farmers don’t spray gallons of Roundup on a crop and immediately feed it to livestock. In most cases, the amount of glyphosate on harvested feed is minimal and would decline while in storage.
“About the only scenario where I could see this happening is when a producer applies Roundup to a pasture and then turns cattle in to graze the remaining aftermath … before reseeding the pasture or plowing it up,” McAllister said.
“(But) it’s unlikely that the producer would (do that).”
In other words, dose is critical.
Glyphosate could affect beneficial microbes in the guts of livestock if the dose was massive.
“Although the mechanism of action of glyphosate is such that it can potentially inhibit some bacteria, in the absence of evidence to the contrary, the concentrations required to do so are likely far above those which would result from consumption of feed … (in) normal farming practice,” said Ed Topp, an Agriculture Canada scientist in London, Ont., who specializes in antimicrobial resistance.
A University of Saskatchewan expert had a similar argument.
If the residue levels are high enough, glyphosate residues could alter some bacterial species in the gut and rumen, said Greg Penner, U of S centennial enhancement chair in ruminant nutritional physiology.
“The potential for glyphosate to impact fermentation in the rumen is real,” he said.
“But what we need to consider are the effective dose rates and the likelihood that cattle could consume enough contaminated crop to attain (such) dose rates.”
Following Dupmeier’s comments in 2017, Penner and other U of S experts received inquiries about glyphosate and cattle health.
After reviewing the relevant science, they decided it’s not a concern.
“The assumed dose rates that cattle could theoretically consume range between 43 parts per million to up to 250 parts per million. That differs based on country and production system,” he said.
Those figures are well above the maximum residue limit of glyphosate for most crops.
The maximum residue limit is 10 p.p.m. for barley and 20 p.p.m. for soybeans.
Even at 40 to 250 p.p.m., cattle health was unaffected.
“At those doses … when measured in test tubes in the lab, there’s very limited effect of glyphosate on microbial fermentation outcomes,” Penner said. “They (researchers) can see some shifts in terms of fermentation profile — very small shifts that we would not expect to have any impact on cattle.”
Glyphosate is not a real antibiotic
Researchers say residues of Roundup on feed, even at higher concentrations, aren’t a threat to livestock health because glyphosate is different from a true antibiotic.
An antibiotic kills certain species of bacteria. Glyphosate does not.
“They are not even comparable,” Penner said.
“Glyphosate does have some antimicrobial activity but it only does this by inhibiting, or partially inhibiting, one metabolic pathway. So, it’s not directly killing microbes. It’s impacting their metabolism. That’s very different.”
As a result, glyphosate is not a broad-spectrum antibiotic and really not an antibiotic at all.
Another thing to consider is that plants use chemicals to fight off pests. Those allelopathic chemicals battle against harmful spores, fungi and bacteria in nature.
“There are anti-microbials in everything we eat…. Plants produce anti-microbials to protect (themselves) against pathogens in the field, so why are we singling this one (glyphosate) out as something that is special?” McAllister said.
Scientists have studied the allelopathic chemicals in plants, such as essential oils, to determine if they are harmful to gut microbes in livestock.
The essential oils can alter the microbe community but not significantly.
If farmers want to improve or alter the microbes in the rumen of cattle, pigs and poultry, they should first look at feed.
An animal on an all-forage diet will have different microbes than cattle fed corn, soybean meal or barley.
“In our experience in working with microbiomes, the number one thing that influences the composition of the microbiome in livestock is the nature of the diet that is fed,” McAllister said.
Should glyphosate be studied to alleviate public fears?
Livestock experts like McAllister, Penner and Topp may not be worried about glyphosate and gut health, but many Americans and Canadians are concerned.
In the 2000s, there were similar concerns about genetically modified crops. A number of scientists studied GM crops used for feed, such as corn and soybeans, to see if the technology was harmful to livestock.
The answer was a resounding no.
Scientists could do something similar with glyphosate residues, McAllister said, but it might be a waste of time.
“You could … spray it on and feed it to the animals, immediately, and look and see if (there is) any impact on the microbiome,” he said.
“My hypothesis is we wouldn’t see anything at all.”