Hair loss and endocrine dermatosis on horses raised in a Mimosa pudica var. unijuga-invaded area.

Hair loss and endocrine-related skin disease were observed in horses grazing in an area invaded by the plant Mimosa pudica var. unijuga. The study investigated the toxic effects of this plant on horses in a specific region in Brazil.

Background and Context

• The research was conducted in Araguari, Triângulo Mineiro, Southeast Brazil, where Mimosa pudica var. unijuga is invasive.
• Mimosa pudica is a plant known for its toxicity, particularly due to an amino acid called mimosine.
• The study focused on a toxicity syndrome in horses associated with grazing on paddocks heavily invaded by this plant.

Clinical Signs and Observations

• Horses grazing for about three months during the dry season exhibited gradual hair loss specifically on the mane and tail.
• In addition to alopecia (hair loss), affected horses developed endocrine dermatosis, a skin disorder related to hormonal or metabolic disturbances.

Histological Findings

• A microscopic examination of the skin revealed compact ortho-keratotic hyperkeratosis, meaning thickening of the outer keratin layer of the skin with normal keratinization.
• There was also evidence of numerous flame follicles, a type of abnormal hair follicle morphology often linked to follicular dysplasia or dysfunction.
• These histopathological changes support a diagnosis of a toxic dermatosis likely linked to metabolic disruptions affecting the skin and hair follicles.

Toxicological Analysis

• Using High-Performance Liquid Chromatography with Ultraviolet detection (HPLC-UV), the researchers quantified the toxin mimosine in the plant leaves.
• The concentration was found to be 0.8 mg of mimosine per gram of leaves.
• Mimosine is a non-protein amino acid known to cause hair loss and interfere with protein synthesis, explaining the clinical and histological findings in horses.

Conclusions and Implications

• Exposure of horses to Mimosa pudica var. unijuga under field conditions can induce a characteristic syndrome of hair loss and endocrine-related skin lesions.
• The presence of mimosine at significant levels in the invasive plant is likely the causative agent.
• This highlights the risk posed by invasive toxic plants in grazing environments and the need for monitoring and management to prevent animal health issues.