Glyphosate is a broad-spectrum herbicide used to control unwanted vegetation in agricultural settings. While designed to target plants, exposure in livestock, including cattle, can occur. For livestock producers, understanding the pathways of exposure, the resulting signs, and prevention measures is necessary.
Pathways to Exposure
The primary way cattle are exposed to glyphosate is through the ingestion of contaminated materials. This can happen when they consume forage, such as hay or silage, that has been directly sprayed or has received spray drift from an adjacent field. Cattle do not actively avoid vegetation that has been treated with glyphosate, making them susceptible to consuming it.
Water sources can also become a route of exposure, as runoff from recently treated fields can contaminate ponds, streams, or drinking troughs. Direct contact is another possibility, such as when animals are accidentally sprayed during application or when they rub against wet, recently treated plants.
Clinical Signs of Toxicity
The clinical signs of acute glyphosate poisoning in cattle primarily involve the gastrointestinal system. Affected animals may exhibit hypersalivation, colic, and diarrhea. Irritation to mucous membranes can result in swelling of the lips and, in some cases, oral ulceration. The severity of these signs depends on the dose ingested. Many commercial glyphosate products contain surfactants, like polyoxyethylene amine (POEA), which are irritants and contribute to the clinical effects.
Beyond immediate gastrointestinal distress, systemic signs can develop in cases of significant exposure. Cattle may become lethargic, weak, and show a loss of appetite. Respiratory distress and tremors have also been reported. The onset of these signs can be rapid, appearing within hours of ingestion, though the mechanism for these systemic effects is not fully understood.
Veterinary Diagnosis and Management
A diagnosis of glyphosate poisoning is often presumptive, based on a history of herbicide use in the vicinity and the presentation of characteristic clinical signs. A veterinarian will consider the timeline of symptom onset in relation to any recent spraying activities on the farm or neighboring properties to rule out other potential causes.
Confirmation can be sought through laboratory analysis of suspected contaminated feed or water. The herbicide and its primary metabolite, aminomethylphosphonic acid (AMPA), can also be detected in the blood and urine of affected animals. These biomarkers are most effective for confirming recent exposure as they are eliminated from the body relatively quickly.
There is no specific antidote for glyphosate poisoning. Treatment is supportive and focuses on decontamination and managing symptoms. This may include administering intravenous fluids to combat dehydration and using gastrointestinal protectants to soothe the digestive tract.
Prevention and Safe Herbicide Use
Prevention requires following the manufacturer’s label instructions for application rates and grazing intervals. These intervals specify the required waiting period before livestock can safely enter a treated area. This waiting period allows the herbicide to dry and begin to break down, reducing the risk of ingestion.
Protecting feed and water supplies from contamination is also a key practice. Feed bunks and water troughs should be covered or located away from areas being sprayed to prevent accidental drift. Store all herbicides in a secure location inaccessible to livestock to prevent ingestion of the concentrated product. Awareness of spraying activities on adjacent properties can also inform temporary management changes, such as moving cattle to a more distant pasture to avoid potential drift.