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Herbicides and horses

Horse Health: A ubiquitous herbicide is beginning to come under increased scrutiny by scientists

The implications for the widespread use of glyphosate-based herbicides in our environment has been increasingly mired in controversy despite regulatory assurances of safety.

After close to three decades of use there is a growing body of scientific evidence emerging which presents unintended biological consequences of this chemical and its formulation. Research is postulating adverse mechanisms of action and implicating glyphosate use as a contributing factor to the rising incidence of chronic inflammation and disease in humans.

Since horses and humans share many of the proposed disrupted biological and ecological pathways it is likely with time, equal concern will be found for the health of the horses.

Application rates for glyphosate-based herbicides have steadily climbed over the last three decades due to: reduced cost of the chemical, adoption of farming practices which use crops which are genetically modified or employ pre-harvest desiccation practices and rising rates of application necessary to further control emerging weed resistance.

Due to its water-soluble nature and formidable application rates its presence has become ubiquitous in the environment. The accumulating burden of glyphosate in the food chains, water sources and the environments of both horses and humans over the last 25 years is a cause for concern especially as recent scientific findings are turning up off-target effects with unexpected ecological connections and outcomes.

The deleterious effects of glyphosate and its formulations arise due to the multiple distinct physical and chemical properties of this unusual synthetic molecule. It has been patented as a broad-spectrum herbicide, mineral chelator, antimicrobial and desiccant. This patent profile portends multiple mechanisms of action upon any biological system with which it interacts.

Originally glyphosate was deemed safe due to the fact that it blocked the shikimate pathway. The shikimate is a metabolic pathway used by bacteria, archaea, fungi, algae, some protozoans, and plants for the biosynthesis of folates and the three essential amino acids, phenylalanine, tyrosine, and tryptophan — but does not exist in humans and animals.

Therefore at one time this disruption was considered to be of no consequence to mammalian biology.

However, when scientists began to look a little deeper into the ramifications of interrupting the shikimate pathway they discovered that the essential amino acids synthesized through this pathway provide vital building blocks for the proteins of animal life. This pathway does not exist in animals and humans because the microbial and plant kingdoms do it for the animal kingdom, acting as an ecological nursemaid for thriving health.

Interruption of metabolic pathways in the microbial communities of the soil and vegetation cannot be discounted as nebulous ‘off-target’ effects since the health of the animal kingdom is intimately interwoven with the health of the plants they consume. And in turn the health of the plant kingdom is intimately interwoven with the health of the soil.

As the burden of glyphosate continues to rise in the environment and enter the food chains of humans and horses, the rich and diverse populations of commensal microbial communities in the digestive tract become disturbed and altered by the antimicrobial properties of glyphosate. Microbiome analysis and its clinical significance is a rapidly advancing field, now being recognized for the critical role it plays in the overall health and wellness of humans and horses. An unbalanced population of micro-organisms within the gut environment is referred to as dysbiosis and has been linked with chronic inflammation and many so-called “modern-day” diseases in the human population. Horses also seem to have accumulated a list of “modern-day” diseases steeped in chronic inflammation.

Glyphosate exposure has also been linked to chronic inflammation via its direct injury to the structural proteins called tight junctions. Tight junctions are the sticky velcro-like protein structures that “spot weld” cells together. These structures knit the cells together that line interfaces. They are found in the cellular linings of the entire gastrointestinal system, sinuses, kidney tubules, and the entire blood vessel tree which includes the liver and the vital blood-brain barrier.

The tight junctions act as intelligent gatekeepers policing passage of substances across the membrane surfaces. When glyphosate injury occurs the integrity of the tight junctions is compromised and indiscriminate “leak” occurs across these boundaries insulting the immune system and inciting inflammation.

Glyphosate has also been implicated in interference of signalling pathways within the body, endocrine and/or hormonal function, gene expression and carcinogenicity.

There is a general agreement that horses today are suffering from more debilitating health issues than was the case two or three decades ago. Given the complexity with which glyphosate is proposed to adversely affect mammalian biology and its increasing prevalence in the food chain and environment of horses, it is plausible that glyphosate exposure may be a contributing factor to illnesses in horses.

The list of clinical suspects include those illnesses associated with gut dysbiosis i.e. gastric and/or hindgut ulceration, equine metabolic diseases i.e. insulin resistance, equine metabolic syndrome, Cushings, chronic inflammation and weaknesses of the musculoskeletal systems, laminitis, weak hoof structure, and liver and kidney disease.

Emerging information postulating mechanisms of functional interference and structural disruption upon the web of ecological health with the use of glyphosate-based herbicides is becoming increasingly difficult to overlook as it ultimately pertains to the health and welfare of horses.

About the author

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Carol Shwetz is a veterinarian focusing on equine practice in Millarville, Alberta.

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