A scientific review in World’s Poultry Science Journal highlights the adverse health effects on avian species from exposure to the widely used weedkiller glyphosate (Roundup) throughout the process of poultry production. The herbicide enters the poultry production system through residues in genetically engineered feed, Beyond Pesticides reported.
An earlier article in Scientific Reports concludes that glyphosate’s (GLP) “widespread application on feed crops leaves residues in the feed,” while residues are “found to be common in conventional eggs acquired from grocery stores.”
In analyzing the biochemical, toxicological and ecological impacts of glyphosate on poultry, particularly chickens, the authors find a wide body of evidence linking glyphosate and its metabolite (breakdown product) aminomethylphosphonic acid (AMPA) to debilitating hazards that extend beyond mortality.
These sublethal effects include disruption of the gut microbiome and gastrointestinal disease; decreased productivity and diminished reproductive health; hepatic and kidney toxicity; growth and developmental impacts, including teratogenicity and embryotoxicity; endocrine disruption and oxidative stress; and impaired immune functions.
The effects of glyphosate, as have long been documented in the scientific literature, range from negative impacts on biodiversity and the environment to food safety risks and human health implications.
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Residues of both glyphosate and AMPA “have been detected in soil, crops, animal feed, poultry, and water sources, prompting scrutiny of their long-term effects,” the authors state.
They continue:
“Studies indicate that glyphosate disrupts enzymatic pathways, particularly by inhibiting the cytochrome P450 system, leading to oxidative stress, endocrine disruption, and mitochondrial dysfunction.
“It has been linked to liver and kidney toxicity, gut microbiota alterations, reproductive harm, developmental defects, and possible carcinogenicity, though regulatory agencies remain divided on its classification as a carcinogen.”
The International Agency for Research on Cancer, a part of the World Health Organization, has classified glyphosate as having cancer-causing properties, as have independent peer-reviewed scientific studies.
The ubiquitous nature of glyphosate residues throughout the environment and within organisms is a result of the widespread application of this toxic chemical in forestry, agriculture, landscaping and gardening.
Over 750 herbicides contain glyphosate as the active ingredient, and it also plays a large role in the production of genetically modified (GM) crops, “with approximately 80% of GM crops bred specifically for GLP tolerance.”
Glyphosate-based herbicide formulations contain not only glyphosate but also other inert (undisclosed) ingredients, such as adjuvants that increase toxicity.
A common adjuvant in glyphosate-based herbicide products is polyethoxylated tallow amine (POEA), which researchers have found can kill human cells, particularly embryonic, placental and umbilical cord cells.
Effects on poultry
Glyphosate residues in animal feed, as well as in water and through other exposure routes, pose risks to both animal and human health, as these residues can bioaccumulate and biomagnify throughout the food chain.
With a high reliance on corn and soybeans in the diets of poultry, GM crops are a significant source of exposure for these animals.
“The presence of GLP residues in poultry feed raises concerns about potential health effects on birds, including disruptions in gut microbiota, oxidative stress, and overall productivity,” the authors write.
They continue:
“Globally, approximately 57% of maize grain and 85% of soybean production are directed towards animal feed. Several studies have investigated the effects of feeding glyphosate-tolerant GM crops to various livestock species.
“Research has included dairy cows, cattle, and chickens, highlighting the potential impact of glyphosate residues on poultry growth performance, immune function, and reproductive health.”
Hepatic and kidney toxicity
Studies show that the kidney and liver are among the first organs to be affected by alimentary poisoning/foodborne illness. Additional research shows glyphosate residues in food can then impact various systems in animals, including the liver, intestine, kidney, and lung, as well as alter enzyme activity.
In a study of hatched chickens exposed to glyphosate alone and in Roundup shows “histopathological alterations in the kidneys and liver, along with imbalances in serum parameters and various biochemical changes in these organs, which could potentially impair their function.”
Oxidative stress
Exposure to glyphosate can induce oxidative stress and lipid, protein, and DNA damage. Previous research shows how glyphosate and AMPA are genotoxic and linked to oxidative damage.
One study shows that glyphosate increases the generation of reactive oxygen species in the liver and small intestine of chickens. Chronic exposure to products containing glyphosate in broiler breeders (stock chickens) weakens eggshells and delays embryo organ growth, with oxidative stress as the cause.
Gastrointestinal toxicity
Glyphosate diminishes the bioavailability of cytochrome (CYP) enzymes, which are crucial for metabolism, in the organs of chickens. One study shows that glyphosate specifically inhibits CYP P450 enzymes in chickens’ livers and small intestines.
Chicks exposed to glyphosate also have compromised liver function and altered lipid metabolism, further causing oxidative stress and deposits of fat in blood and liver tissues due to heightened expression of lipogenesis-related genes, as a result of its disruptive effect on cytochrome P450 enzymes.
Additional studies show disruption of the gut microbiome in livestock and poultry, where glyphosate reduces beneficial bacteria and enhances resistance in pathogenic strains.
These impacts can lead to the onset of chronic gastrointestinal diseases. In a study of the intestinal structure of chicks, glyphosate has been shown to impair the intestines, reduce antioxidant capacity, induce inflammation and cause the downregulation of genes in the small intestine.
Impact on reproduction
Previous research shows that chronic exposure to herbicides containing glyphosate can impact the survival, growth, activity and reproduction of organisms, including chickens.
A study of roosters with chronic, subtoxic exposure to glyphosate shows reduced plasma testosterone and a decline in their reproductive peak.
Another study finds “significant effect on the histopathological [diseased tissue] characteristics of the rooster testes as well as sperm motility, the key determinant of rooster sperm quality.”
Additional research shows altered sperm in roosters when fed a diet containing glyphosate that leads to “metabolic disorders in the offspring, most likely due to epigenetic effects.”
Glyphosate implications for productivity and performance
Several studies have classified glyphosate-based herbicide formulations as teratogenic, causing developmental abnormalities in a fetus or embryo, and embryotoxic, causing harm or death to embryos during development.
In a study of quails, glyphosate was found to accumulate inside the eggs, causing damage to lipids (fats) in the brains of the developing embryos. This study also reveals that residues of glyphosate in food also slow plumage development and linger in eggs, muscles and livers of the birds.
Another study of chickens shows “exposure to GLP led to a significant reduction in the expression of key productivity-related genes.”
Exposure directly in the eggs of chickens to glyphosate-based herbicides induces teratogenic effects with negative effects on embryonic growth and development, as well as embryo mortality.
Changes in blood parameters, adverse effects on digestive tract development and reduced body weight are noted in chickens exposed to glyphosate.
Reproductive and developmental impacts regarding eggshell quality and embryo development are also associated with levels of both glyphosate and AMPA within egg yolk.
Yet another study shows that a decline in hatchability is associated with higher levels of glyphosate residues in feed among broiler breeders.
Regulatory deficiencies and the organic solution
Despite mounting scientific evidence that continues to link glyphosate to adverse effects in a wide range of species, current regulations fail to protect health and the environment.
The regulatory processes, such as those utilized by the U.S. Environmental Protection Agency (EPA), also ignore factors that enhance the toxicity of these already harmful chemicals, such as synergy, mixtures and inert ingredients.
“Current safety evaluations mostly concentrate on glyphosate in isolation, overlooking the synergistic toxic effects of commercial formulations and their capacity for bioaccumulation in adipose tissues,” the authors point out.
They continue:
“Furthermore, the heightened toxicity of commercial glyphosate formulations, influenced by co-formulants such as POEA, in conjunction with glyphosate’s interference with gut microbiota, cytochrome P450 enzymes, and endocrine functions, emphasises the necessity for cumulative risk assessments and long-term studies that account for species variability, bioaccumulation, and synergistic effects.”
These inadequacies in the regulation of petrochemical pesticides and synthetic fertilizers support the urgent need for the widespread adoption of safer alternatives.
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