A recent scientific review published in the World’s Poultry Science Journal has raised concerns about the health impacts of glyphosate, a widely used weedkiller, on poultry. The herbicide can enter the poultry production system through residues found in genetically engineered (GE) feed. These residues have also been detected in conventional eggs bought from supermarkets.
The review analysed numerous studies on the biochemical, toxicological, and ecological effects of glyphosate and its breakdown product, aminomethylphosphonic acid (AMPA), on poultry, particularly chickens. The findings highlight a significant body of evidence linking these chemicals to serious health problems in birds. These issues go beyond just mortality and include disruptions to the gut microbiome, gastrointestinal diseases, reduced productivity, and impaired reproductive health.
Furthermore, the research points to toxicity in the liver and kidneys, issues with growth and development (including birth defects and embryo harm), disruption of the endocrine system, and increased oxidative stress. The immune functions of the birds can also be weakened. These effects are not unique to poultry and have been previously documented in scientific literature concerning wider environmental impacts, food safety, and human health.
Glyphosate and AMPA residues have been found in various parts of the production cycle, including soil, crops, animal feed, poultry products, and water. This widespread presence has led to increased scrutiny of their long-term effects. Studies suggest that glyphosate interferes with essential biological pathways, such as the cytochrome P450 system. This interference can lead to oxidative stress, endocrine disruption, and problems with mitochondria, which are vital for cell energy.
The International Agency for Research on Cancer, part of the World Health Organization, has classified glyphosate as a potential carcinogen, a view supported by independent scientific research. The extensive use of glyphosate in agriculture, forestry, and landscaping, along with its role in the production of GE crops (about 80% of which are bred to tolerate glyphosate), contributes to its pervasive presence.
Many glyphosate-based herbicides contain additional ingredients, known as adjuvants, which can increase toxicity. Polyethoxylated tallow amine (POEA), a common adjuvant, has been found to harm human cells, including those of embryos.
For poultry, the presence of glyphosate residues in feed is a major concern. With corn and soybeans being staple components of poultry diets, and a large percentage of these crops being genetically modified, exposure is significant. Studies have investigated the effects of feeding glyphosate-tolerant GE crops to livestock, including chickens, focusing on growth, immune response, and reproduction.
Research indicates that the liver and kidneys are particularly vulnerable to toxins found in food. Glyphosate residues can affect these organs and other systems, altering enzyme activity. Studies on chickens exposed to glyphosate have shown physical damage to the kidneys and liver, as well as imbalances in blood markers and biochemical changes within these organs, potentially affecting their function.
Glyphosate exposure can also lead to oxidative stress, damaging cells and DNA. In chickens, this has been linked to reduced eggshell strength and delayed embryo development. It also impairs the function of cytochrome P450 enzymes in the liver and small intestine, which are crucial for metabolising substances. This can lead to compromised liver function, altered fat metabolism, and fat accumulation in tissues.
Additionally, glyphosate can disrupt the gut microbiome, reducing beneficial bacteria and increasing the prevalence of harmful ones, potentially leading to chronic digestive diseases. Studies have shown that glyphosate can damage the intestinal structure, reduce antioxidant defence, cause inflammation, and alter gene expression in the small intestine of chicks.
Reproductive health is also affected. Chronic exposure to glyphosate-containing herbicides has been linked to reduced sperm quality and lower testosterone levels in roosters. This can lead to metabolic disorders in offspring, possibly due to epigenetic changes.
Glyphosate-based herbicides have also been classified as teratogenic (causing birth defects) and embryotoxic (harmful to embryos). In quail, glyphosate has been found to accumulate in eggs, damaging the brains of developing embryos. It can also slow feather development and remain in eggs, muscles, and livers.
Studies on chickens have shown a significant reduction in the expression of genes related to productivity. Exposure to glyphosate in eggs can cause birth defects, negatively impact embryonic development, and increase embryo mortality. Changes in blood parameters, digestive tract development, and reduced body weight have also been observed.
Despite this growing body of evidence, current regulations are often seen as insufficient to protect health and the environment. Regulatory bodies may not fully consider the synergistic effects of chemical mixtures or the toxicity of inactive ingredients found in pesticide formulations. The review authors emphasise the need for cumulative risk assessments that account for bioaccumulation, synergistic effects, and variations between species.
The inadequacies in regulating synthetic pesticides and fertilisers highlight the urgent need for safer alternatives, such as organic farming practices, to ensure the health of both animals and consumers.