Alfalfa hay induced primary photosensitization in horses.
Abstract: Photosensitization, also known as photodermatitis, occurs when phototoxic or photoactive substances accumulate in the skin and interact with sunlight to result in an often severe, crusting, itching or painful dermatitis in unpigmented and/or lightly haired areas of the skin. Primary photosensitization, caused by direct ingestion of photosensitizing agents, has been reported anecdotally in horses after ingestion of alfalfa hay. Between 2004 and 2014, several large outbreaks of primary photosensitization in horses fed primarily alfalfa hay were investigated in California. Alfalfa hay samples were collected and carefully examined for the presence of known photosensitizing plants and pesticide residues but none were identified. Select hay samples were evaluated for unusual fungal infestation and for phototoxicity assay using a specific Candida albicans assay; results were negative. In the 2004 outbreak, a feeding study was conducted with three horses exclusively fed alfalfa hay that was suspected to have caused the outbreak. Two weeks after ingestion of alfalfa hay, two horses developed several lesions in non-pigmented skin characterized as chronic ulcerative and necrotizing dermatitis with superficial vasculitis, which was consistent with photosensitization. In the 2014 outbreak, seven different implicated alfalfa hay samples were analyzed for chlorophyll a and b, and pheophorbide a. These compounds had been suspected to play a role in alfalfa-induced primary photosensitization. The chlorophyll contents ranged from 0.90 to 2.30 mg/g in the alfalfa hay samples, compared to 1.37 and 2.94 mg/g in locally grown alfalfa and orchard grass hay. The pheophorbide a levels ranged from 3.36 to 89.87 µg/g in alfalfa samples compared to 81.39 and 42.33 µg/g in control alfalfa and orchard grass hay samples. These findings eliminate chlorophyll a, chlorophyll b, and pheophorbide a as possible causes for alfalfa-hay induced primary photosensitization.
Copyright © 2016 Elsevier Ltd. All rights reserved.
Publication Date: 2016-03-17 PubMed ID: 27040919DOI: 10.1016/j.tvjl.2016.03.004Google Scholar: Lookup
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Summary
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This study investigates the cause of primary photosensitization in horses, a condition that can lead to severe skin dermatitis. After noticing several outbreaks among horses fed primarily on alfalfa hay in California, the researchers explored various potential causes such as photosensitizing plants, pesticide residues, fungal infestations and phototoxicity, but found none. The researchers then conducted feeding studies which provided strong evidence that the condition was caused by the alfalfa hay. However, further testing ruled out chlorophyll a, chlorophyll b, and pheophorbide a as the specific causes of the condition.
Context
- This study was prompted by outbreaks of primary photosensitization in horses in California between 2004 and 2014. This condition, also known as photodermatitis, is often painful and can cause severe, crusty, itchy skin inflammations, especially in unpigmented or lightly-haired areas.
- Earlier anecdotal reports had suggested a link between consumption of alfalfa hay and the condition, but no definitive cause had been identified.
Research Methodology
- The researchers collected and analyzed samples of the alfalfa hay fed to the affected horses, looking for potential triggers for the condition.
- They checked these samples for the presence of known photosensitizing plants and pesticide residues, for unusual fungal infestations, and for phototoxicity using a specific Candida albicans assay. All these tests came back negative.
- They then conducted feeding studies with horses, feeding them only the alfalfa hay suspected of causing the problem. After about two weeks, two of the three horses in the 2004 study developed symptoms consistent with photosensitization.
Findings and Conclusion
- In a 2014 outbreak, the researchers examined seven alfalfa hay samples, this time testing for chlorophyll a and b and pheophorbide a. These compounds are known to be potentially phototoxic and had been suspected of playing a role in alfalfa-induced photosensitization.
- However, the presence of these substances in the alfalfa hay samples was not significantly different from their presence in control samples of locally grown alfalfa and orchard grass hay. Therefore, they were ruled out as potential causes of the photosensitization.
- This leaves the specific cause of the alfalfa hay-induced photosensitization unknown, requiring further investigation.
Cite This Article
APA
Puschner B, Chen X, Read D, Affolter VK.
(2016).
Alfalfa hay induced primary photosensitization in horses.
Vet J, 211, 32-38.
https://doi.org/10.1016/j.tvjl.2016.03.004 Publication
Researcher Affiliations
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California, 1089 Veterinary Medicine Drive, Davis, CA 95616, USA. Electronic address: bpuschner@ucdavis.edu.
- Department of Molecular Biosciences, School of Veterinary Medicine, University of California, 1089 Veterinary Medicine Drive, Davis, CA 95616, USA.
- California Animal Health and Food Safety Laboratory System, San Bernadino Branch, 105 W. Central Avenue, San Bernardino, CA 92408, USA.
- Department of Pathology, Microbiology, Immunology, School of Veterinary Medicine, University of California, Davis, One Shields Avenue, Davis, CA 95616, USA.
MeSH Terms
- Animal Feed / adverse effects
- Animals
- California / epidemiology
- Chlorophyll / analogs & derivatives
- Chlorophyll / analysis
- Chlorophyll A
- Diet / veterinary
- Disease Outbreaks / veterinary
- Female
- Horse Diseases / epidemiology
- Horse Diseases / etiology
- Horses
- Male
- Medicago sativa / chemistry
- Photosensitivity Disorders / epidemiology
- Photosensitivity Disorders / etiology
- Photosensitivity Disorders / veterinary
- Silage / adverse effects
Citations
This article has been cited 4 times.- Murotomi K, Umeno A, Shichiri M, Tanito M, Yoshida Y. Significance of Singlet Oxygen Molecule in Pathologies.. Int J Mol Sci 2023 Feb 1;24(3).
- Collett MG. Photosensitisation diseases of animals: Classification and a weight of evidence approach to primary causes.. Toxicon X 2019 Jul;3:100012.
- Chen Y, Quinn JC, Weston LA, Loukopoulos P. The aetiology, prevalence and morbidity of outbreaks of photosensitisation in livestock: A review.. PLoS One 2019;14(2):e0211625.
- Quinn JC, Chen Y, Hackney B, Tufail MS, Weston LA, Loukopoulos P. Acute-onset high-morbidity primary photosensitisation in sheep associated with consumption of the Casbah and Mauro cultivars of the pasture legume Biserrula.. BMC Vet Res 2018 Jan 11;14(1):11.
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