Toxic plants affecting livestock in South America: Review of epidemiology, diagnosis, control, economic impact and implications to human health.

Overview

• This research article reviews toxic plants that affect livestock such as ruminants and horses in South America, focusing on their epidemiology, diagnosis, control, economic impact, and implications for human health.
• It emphasizes the diversity of toxic plants, factors influencing toxicity, methods for diagnosis and control, and calls for strengthened research efforts in the region.

Introduction to Toxic Plants in South America

• South America is home to 237 known plants toxic to livestock, particularly ruminants (like cattle and sheep) and horses.
• Toxic plants interfere significantly with livestock health, causing economic losses and potentially impacting human health indirectly.
• Both native and invasive plants can be toxic; invasive species may originate within the continent or from other regions.

Factors Predisposing to Plant Toxicity

• Plant Characteristics: Toxicity can depend on the specific part of the plant consumed (leaves, seeds, roots) or its vegetative stage (e.g., sprouting after rains).
• Dose of Toxic Compound: The amount ingested determines whether toxicity manifests, as some plants can be harmless in small quantities.
• Animal Behavior and Condition: Hunger, thirst, palatability of the plant, social facilitation (animals copying others), and naivete (lack of previous exposure) influence ingestion risk.
• Susceptibility Factors: Variations in species, individual resistance/susceptibility, transportation stress, and environmental conditions like climate and habitat degradation.

Types of Toxic Plants Affecting Livestock

• Forage Species: Plants naturally consumed as feed but toxic in certain conditions or amounts.
• Non-Forage Species: Plants not normally consumed intentionally, including invasive species that encroach on grazing areas.

Diagnosis of Plant Poisoning

• Known Toxic Compounds: Diagnosis involves confirming the presence of active toxic substances in plants or affected animals.
• Clinical and Pathological Evaluation: Identification of clinical signs in animals, alongside clinical and anatomical pathology findings, such as lesions found during necropsy.
• Unknown Toxins: Diagnosis relies more heavily on epidemiological data and clinical observation since toxic compounds are unidentified.

Control and Prevention Strategies

• Management Practices: Adjusting grazing patterns, removing toxic plants, or improving pasture quality to reduce exposure.
• Biological Control: Using natural predators or competitive plants to reduce toxic plant populations.
• Conditioned Food Aversion: Training animals to avoid certain plants by associating them with unpleasant experiences.
• Integrated Control Strategies: Combining multiple approaches for effective and sustainable management.
• Prophylactic Approaches: Focusing on enhancing natural or induced resistance in animals and implementing preventive management before outbreaks occur.

Economic Impact and Research Gaps

• Plant poisonings result in substantial economic losses across South American livestock industries, affecting productivity and animal health.
• Despite this significant impact, many regions and countries have insufficient research and data on toxic plants.
• The authors highlight the need for establishing new research groups to advance understanding, diagnosis, and control of poisonous plants in South America.

Implications for Human Health

• Although livestock are the primary victims, toxic plants can have indirect effects on human health through contaminated animal products or economic impact on farmers.
• Understanding and controlling plant toxicity is important to protect food safety and rural livelihoods.