Chicken and eggs sit quietly in most New Zealand kitchens — slipped into lunchboxes, thrown into stir-fries, or turned into quick mid-week dinners.
They’re foods we trust without a second thought. But beneath that sense of simplicity is a blind spot most consumers never even consider: glyphosate, better known by its brand name, Roundup®.
A new peer-reviewed review published in the World’s Poultry Science Journal (August 2025) has pulled back the curtain on something the poultry industry has never been especially eager to talk about. The researchers looked at how glyphosate-based herbicides move through the modern poultry system — and what they found should give every chicken-eating household pause.
Glyphosate doesn’t stay in the fields where it’s sprayed. It travels through genetically modified soy and maize feed, into the guts and organs of the birds, and in some cases all the way into egg yolks, muscle tissue, and liver. Its breakdown product, AMPA (aminomethylphosphonic acid), shows up too.
The question this raises isn’t theoretical or alarmist — it’s practical:
If Roundup damages the health of the birds themselves, what does that mean for the people who eat them?
How Glyphosate Enters the Poultry Food Chain
Most people picture Roundup being sprayed on paddocks or roadside verges. But in reality, New Zealand poultry farms rely heavily on imported GM soy and maize feed, grown in countries where glyphosate use is intense and widespread. These crops are engineered to survive repeated spraying — and as a result, residues are common.
Once chickens ingest glyphosate, it doesn’t simply pass through.
Studies show that glyphosate and AMPA can accumulate in organs, particularly the:
- liver
- kidneys
- muscle tissue
- and even egg yolks
It shouldn’t be surprising that a chemical designed to penetrate plant cells can also penetrate animal systems — but it’s something our regulators rarely acknowledge.
And while regulators assess “glyphosate” as a single chemical, real-world products like Roundup® contain additional surfactants and adjuvants (often undisclosed) that increase absorption and toxicity. One example, POEA, is well-documented to increase cell penetration far beyond glyphosate alone.
So what starts as a herbicide on feed crops quietly becomes part of the poultry production cycle. And once it’s in the birds, it becomes part of our food supply too.
What Glyphosate Does to Poultry Health
The new poultry review paints a picture that is anything but benign. Glyphosate exposure affects nearly every biological system in the birds, often in ways that farmers can’t see immediately — but which matter enormously over time.
Gut Health Disruption and Immune Weakness
The gut microbiome is the foundation of poultry health. It determines how well birds absorb nutrients, how strong their immune system is, and how resilient they are to disease outbreaks.
Glyphosate disrupts this balance by:
- suppressing beneficial bacteria
- enabling harmful strains to flourish
- increasing vulnerability to infections
If you’ve ever cracked an egg with a thin shell or noticed chickens succumbing quickly to disease, gut stress is often part of the story — and glyphosate makes that underlying weakness worse.
Liver and Kidney Damage
The liver and kidneys are the body’s detox engines. But glyphosate residues accumulate in both organs, and studies show:
- tissue damage
- enzyme disruption
- biochemical imbalances
These changes don’t just hurt the birds; they raise obvious questions about what ends up in the final food product.
Oxidative Stress and Cellular Damage
Glyphosate and AMPA trigger oxidative stress — a process that damages DNA, proteins, and cell membranes. In chickens and embryos, this can lead to:
- weak eggshells
- slowed organ development
- impaired growth
- long-term cellular damage
Oxidative stress is one of the most consistent findings across glyphosate research, and poultry are no exception.
Reproductive Effects and Embryo Development Problems
Studies of roosters and breeding hens show that chronic, low-level exposure can:
- lower testosterone
- damage sperm quality
- alter reproductive tissue
- weaken eggshell structure
- reduce hatchability
- increase developmental abnormalities in embryos
These aren’t just “productivity losses.” They’re signs of system-wide biological interference.
Growth, Weight Gain, and Productivity Declines
Glyphosate-exposed birds often show:
- slower weight gain
- poorer feed efficiency
- weaker immune performance
Residues found in muscle and egg yolks make it clear that these aren’t abstract lab effects — they have real implications for the food on the table.
Environmental Spread and Human Health Parallels
The story doesn’t stop at the farm gate. What happens in poultry mirrors what happens in ecosystems — and potentially in humans.
Glyphosate Persists in Soil, Water, and Wildlife
Residues don’t break down quickly.
They disrupt:
- soil microorganisms
- aquatic ecosystems
- pollinators
- invertebrates
The same patterns — oxidative stress, endocrine disruption, and cellular damage — show up across species.
Bioaccumulation in the Food Chain
When residues appear in eggs, liver, and meat, consumers become the final link in the chain. And yes — residues have been detected in conventional eggs overseas.
Human Health Mechanisms Look Strikingly Similar
The same biological disruptions seen in poultry appear in mammalian studies, including human cell cultures:
- oxidative stress
- cytochrome P450 disruption
- endocrine interference
- liver and kidney toxicity
And of course, the International Agency for Research on Cancer (IARC) has classified glyphosate as “probably carcinogenic to humans.”
Why Regulators Keep Missing the Bigger Picture
Perhaps the most troubling aspect of the poultry review is how sharply it contrasts with the story regulators tell the public.
Glyphosate Is Assessed Alone, Not As Roundup®
Regulators test “glyphosate” as a single molecule.
But real-world exposures come from glyphosate-based herbicides (GBHs) — mixtures with adjuvants designed to increase penetration and persistence.
These mixtures are often far more toxic than glyphosate itself.
Yet they’re not part of regulatory testing.
Focus on Short-Term Harm, Not Long-Term Effects
Regulatory frameworks emphasise:
- acute toxicity
- short-term effects
- large single exposures
What gets missed?
Exactly what poultry research highlights:
- chronic exposure
- low doses
- bioaccumulation
- endocrine effects
- oxidative stress
- reproductive changes
Conflicting Classifications Create False Reassurance
IARC says “probably carcinogenic.”
EPA and EFSA say “unlikely carcinogenic.”
Consumers, farmers, and animal owners are left navigating conflicting interpretations — while the birds and the environment feel the impact regardless.
The Problem of Chemical “Cocktails”
Poultry and humans are rarely exposed to one chemical at a time.
But regulators still assess pesticides one by one, ignoring cumulative or synergistic effects.
This is not how biology works.
And it’s not how real farms work either.
Certified Organic Poultry: A Safer Alternative
If glyphosate in the poultry system reveals what’s broken, certified organic offers a glimpse of what’s possible.
Organic systems must use:
- feed grown without synthetic herbicides
- soil-building practices
- biodiversity protection
- stronger animal welfare measures
The difference in outcomes is striking.
Healthier Birds, Cleaner Products
Studies comparing organic and conventional birds show:
- stronger immune systems
- lower oxidative stress
- reduced antibiotic-resistant infections
But even “organic” isn’t foolproof:
Overseas testing has found residues in some supposed “organic” eggs due to spray drift or contaminated supply chains.
That’s why Certified Organic standards and audits matter.
Environmental Protection Benefits Go Further
Certified Organic farming reduces:
- chemical drift
- contaminated runoff
- damage to soil biology
- biodiversity decline
It is, quite simply, the more resilient system.
Economic and Social Benefits Over the Long Term
Organic products cost more up front, but fewer hidden costs land on:
- the health system
- environmental restoration funds
- future generations
Consumers aren’t subsidising the consequences of chemical-heavy agriculture.
How Long Can New Zealand Pretend This Is Safe?
The poultry review makes something uncomfortably clear:
A herbicide designed for weeds is ending up in chickens, eggs, and ultimately human diets. And regulators are still treating it as an invisible background chemical.
New Zealand can change this — but only if we acknowledge what the research is telling us.
Practical steps are within reach:
- stronger independent testing of poultry products
- tighter oversight of imported feed
- support for certified organic production
- public transparency about residues in animal feed
And for consumers, the first step is simply refusing to accept that this is “just how the system works.”
Every choice we make — every egg we buy, every producer we support, every question we ask at the supermarket — helps shift the food chain toward something safer and more honest.
Because once you know that a chemical can travel from crop to chicken to consumer, the real question becomes:
How long are we willing to look the other way?
Resources & References
Before drawing conclusions, it’s worth exploring the wider research that underpins these findings. The studies and reviews below provide a deeper look into glyphosate’s role in poultry production, its impacts on animal and human health, and the broader regulatory and environmental context.
Glyphosate in poultry production: health risks, toxicity, and environmental impact.
World’s Poultry Science Journal.
Fathi, M. et al. (2025).
Peer-reviewed review analysing the biochemical, toxicological, and ecological effects of glyphosate (Roundup®) in poultry. Highlights organ toxicity, gut disruption, reproductive harm, and the shortcomings of regulatory oversight.
Potential toxic effects of glyphosate and its commercial formulations.
Food and Chemical Toxicology, 84, 133–153.
Mesnage, R. et al. (2015).
Review showing that glyphosate-based herbicides (GBHs) are more toxic than glyphosate alone due to adjuvants like POEA.
Glyphosate Monograph 112: Evaluation of five organophosphate insecticides and herbicides.
International Agency for Research on Cancer (IARC). (2015)
The WHO’s cancer research body classified glyphosate as “probably carcinogenic to humans,” sparking global debate and regulatory controversy.
Environmental and health effects of the herbicide glyphosate.
Science of the Total Environment, 616–617, 255–268.
Van Bruggen, A.H.C. et al. (2018)
Comprehensive review of glyphosate’s impacts on soil health, microbiota, biodiversity, and long-term human health risks.
Read study
No More Glyphosate NZ – Related Articles
Why Glyphosate Isn’t Just a Weed Killer — It’s a Public Health Issue
Exploring how glyphosate affects far more than weeds, including the food we eat and the health of future generations.
Glyphosate and Hormone Disruption: What We Know So Far
Review of emerging evidence that glyphosate interferes with the endocrine system.
Why Raising MRLs Threatens Public Health
Analysis of New Zealand’s proposal to raise glyphosate residue limits on staple crops and what it means for consumers.
These resources make one thing clear: glyphosate-based weedkillers such as Roundup® aren’t just a farm input — they thread their way from soil and feed into animals, food, and ultimately people. The science is building, but so too is the silence of regulators. If even poultry, one of the most intensively studied food animals, shows such vulnerability, what does that say about the wider food system we’ve built?
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