Updated August 2026: Since this article was first published, NMGNZ has undertaken a detailed review of MPI’s milk-monitoring records. We have updated this article to reflect what we found, including evidence of longstanding glyphosate testing in raw milk and MPI’s annual survey of processed fresh milk and cream.
Most people imagine New Zealand dairy cows wandering through clean, green paddocks, eating natural grass in fresh air.
It’s part of our national identity — and the foundation of our export marketing. But dairy cows can also be exposed to glyphosate residues through pasture and supplementary feed.
We know some New Zealand farmers use glyphosate in pasture-management practices that can result in treated vegetation being grazed or fed to livestock. That raises a straightforward question: what happens when dairy cows consume glyphosate residues in their feed?
And the question isn’t only what happens inside the animal.
New Zealand does routinely test raw milk collected at the farm for glyphosate through MPI’s National Chemical Contaminants Programme. What appears to be much less common is testing of the finished fresh milk consumers actually buy. We have also found that MPI has conducted an annual survey of processed retail milk and cream for glyphosate and AMPA since 2015.
If we want honesty and transparency in our food chain, we need to understand what this actually means for animal health — and for the people consuming the end products.
What Does the Research Say About Glyphosate and Cow Health?
Dairy cows can be exposed to glyphosate residues through contaminated pasture and feed, which raises an obvious question: what happens once those residues are consumed? Researchers have investigated possible effects on the rumen, liver, blood, metabolism, reproduction and milk production. The results are more mixed — and in several respects more reassuring — than this article originally suggested.
What Does Glyphosate Do to the Rumen?
Because glyphosate targets the shikimate pathway found in plants and many microorganisms, researchers have investigated whether residues in feed could alter the complex microbial community in a cow’s rumen.
Laboratory rumen studies have reported some changes in fermentation measures after glyphosate exposure, which helped raise the question. However, controlled studies in dairy cows have not demonstrated the widespread rumen disruption sometimes attributed to glyphosate. One in-vivo study using glyphosate-contaminated feed found no adverse effect on rumen microbial composition, diversity or microbial metabolites under the conditions tested.
That does not prove that every exposure level, formulation or feeding situation is without effect. But the current dairy-cow evidence does not support saying that glyphosate routinely tips the rumen microbiome out of balance.
What About the Liver and Other Metabolic Effects?
The liver is an obvious organ to investigate because it plays a central role in metabolism and processing foreign compounds. Laboratory-animal studies have reported liver and kidney effects at some glyphosate exposures, but findings in dairy cows have been considerably more reassuring.
In a controlled feeding study designed to reflect relatively high practical exposure through contaminated feed, researchers found no adverse glyphosate-related effects on liver histology, key biochemical blood measures or general animal-health characteristics under the conditions tested.
That distinction matters. Effects reported in laboratory animals or cell studies cannot automatically be assumed to occur in dairy cows consuming residues through normal feed.
How Much Does New Zealand Test Milk for Glyphosate?
New Zealand’s dairy monitoring is more extensive than we originally understood when this article was published.
MPI’s National Chemical Contaminants Programme routinely samples raw milk from individual farms and tests selected samples for glyphosate. Published records show glyphosate testing going back at least to 2011/12, and AMPA, its principal breakdown product, has also been included in the monitoring programme.
There has also been testing further along the supply chain. In 2015, MPI collected 60 commercially available processed milk and cream products from retail outlets and tested them specifically for glyphosate and AMPA. Neither was reported as detected.
Why Glyphosate-Sprayed Feed Still Deserves Scrutiny
The dairy sector relies on public trust, export credibility and confidence that New Zealand’s food-safety systems are robust. Glyphosate residues can occur in animal feed, which makes continued monitoring and research worthwhile — not because we have established that glyphosate in feed is harming New Zealand dairy cows or contaminating their milk, but because those are questions that should be answered with evidence rather than assumptions.
New Zealand’s published raw-milk results are reassuring. At the same time, questions remain about the extent of testing of finished retail milk, changes in reporting limits over time, and the residues dairy cows may encounter through pasture and supplementary feed.
The stronger the evidence, the stronger the reassurance — whichever way the evidence points.
Resources & References
The research into glyphosate exposure in dairy cattle does not tell a simple story. Some findings have raised questions worth investigating, while controlled studies have also produced reassuring results. The studies below are among those we used to look more closely at what happens when dairy cows consume glyphosate residues through their feed.
They also help separate what has actually been demonstrated in dairy cattle from effects proposed through laboratory studies, biological mechanisms or research in other species. That distinction matters when asking what the evidence can — and cannot — tell us about New Zealand dairy cows.
Peer-Reviewed Studies in Dairy Cattle
Influences of Glyphosate Residues in Dairy Cow Rations
(Heymann et al., 2023 — PLOS ONE)
This controlled study followed cows exposed to glyphosate residues during part of gestation and examined blood, immune-function and DNA-damage measures in the cows and their newborn calves. Some individual measures differed between groups, but the researchers concluded that they found no evidence of teratogenic or other clear glyphosate-related effects under the conditions tested. They noted that studies covering later or complete gestation would be needed to address remaining uncertainty.
https://journals.plos.org/plosone/article?id=10.1371/journal.pone.0286995
Excretion Pathways and Ruminal Disappearance of Glyphosate
(Journal of Dairy Science, 2016)
This dairy-cow study investigated what happens to glyphosate and AMPA consumed in feed. Most glyphosate was eliminated via faeces, with some urinary excretion, while elimination in milk was negligible. The study is useful for understanding exposure and excretion rather than establishing adverse health effects.
https://www.journalofdairyscience.org/article/S0022-0302(16)30187-4/fulltext
Effects of Glyphosate Contamination in Dairy Cow Diet
(Jandee et al., 2025)
A small controlled feeding study involving three lactating cows exposed to different glyphosate concentrations. The researchers found no effect on feed intake, milk yield or overall milk composition, although lactose production decreased at the higher exposure and some white blood-cell proportions changed. The very small sample size means the findings should be interpreted cautiously.
https://kasetsartjournal.ku.ac.th/abstractShow.aspx?param=YXJ0aWNsZUlEPTg2MTR8bWVkaWFJRD05MzE2
Contextual and Mixed-Quality Evidence
Glyphosate in Livestock: Feed Residues and Animal Health
(Vicini et al., 2019 — Journal of Animal Science)
A review examining glyphosate residues in livestock feed and the available evidence concerning exposure and animal health. The authors concluded that reported dietary exposures were substantially below levels expected to cause adverse effects.
URL: https://academic.oup.com/jas/article/97/11/4509/5565412
Investigations on Glyphosate Herbicide Impact on Ruminal Metabolism
(Riede et al., 2016)
An in-vitro rumen simulation study investigating whether a glyphosate-containing herbicide affected ruminal metabolism and bacterial communities. Under the experimental conditions used, the researchers did not find evidence of adverse effects on ruminal metabolism or bacterial community composition. As an in-vitro study, it cannot answer every question about exposure in living dairy cows.
URL: https://academic.oup.com/jambio/article/121/3/644/6717318
Together, these studies raise important questions about what happens when dairy cows consume glyphosate residues in feed. New Zealand does monitor raw milk for glyphosate, with published results so far providing reassuring non-detects. The question we are now investigating is how closely finished retail milk is monitored — and whether today’s testing is sensitive enough to detect very low residues.
Related Articles
How Glyphosate Gets Into Our Food
A clear explainer of how pre-harvest spraying and fed crops introduce glyphosate into the food chain.
https://nomoreglyphosate.nz/how-glyphosate-gets-into-our-food/
If New Zealand Tested for Glyphosate, What Would They Find?
Looks at overseas residue data and NZ’s lack of testing, then asks what a proper national survey might reveal in everyday foods like cereals, bread and snacks.
https://nomoreglyphosate.nz/if-new-zealand-tested-for-glyphosate/
What Glyphosate Is Doing to Your Microbiome
Explores how glyphosate affects gut health — relevant to rumen function and cow health.
https://nomoreglyphosate.nz/glyphosate-microbiome-impact/
Death by a Thousand Cuts: Chronic Low-Level Chemical Exposure
Connects the dots between repeated low-dose exposure and long-term health effects in both animals and humans.
https://criticalmindshift.com/death-by-a-thousand-cuts-chemical-exposure/
When you start connecting these dots, the question isn’t whether New Zealand tests milk for glyphosate. It does. The more useful questions are how often we test, how sensitive those tests are, what happens to residues present in feed — and how closely we monitor the finished milk consumers actually take home.
Those are questions we are now investigating.
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