tbtrailrider
Sep. 12, 2009, 08:46 PM
I am caring for a horse that has been diagnosed with this...anyone here have any experience with it? The filly I am caring for is mostly white, and has broken out in hives all over. The vet recommended keeping her out of the sun, and keeping her off pasture, as it could be any number of things she is eating that causes it, but her hives have not gone away and it has been 3 weeks.
This is what I found online...
Primary Photosensitization
Photosensitivity is commonly seen as a result of ingesting photodynamic agents from a number of plant and chemical toxins. When an animal consumes a plant or chemical containing these pigments (e.g., polyphenolic), the pigments circulate to the skin where they are exposed to UV light, fluoresce and cause oxidative injury to the cells of the skin (1). Buckwheat and St. John's wort cause primary photosensitization (1). Phosphorus fertilizer, coal tar pitch, wood preservatives, pentachloro-phenols, aflatoxin B in moldy feed, as well as a number of veterinary medicines, such as tetracycline and phenothiazine tranquilizers, can all act as photodynamic agents, absorbing the ultraviolet light and passing the energy to adjacent cells resulting in cell damage (1, 2).
Secondary Photosensitization occurs when a toxin damages the liver and results in the inability to excrete phylloerythrin. Phylloerythrin is a porphyrin compound formed by microbial degradation of chlorophyll in the gut. It is normally removed by the liver and excreted in the bile (1). If the liver is severely diseased, phylloerythrin accumulates in the blood. As it circulates through to the skin, it is exposed to UV light, fluoresces and causes oxidative injury to the blood vessels and tissues of the skin (1). Pyrrolizidine alkaloid is the most important causative agent in this group. Tansy ragwort, groundsel, fiddleneck, common heliotrope, vipers bugloss, and rattlebox contain pyrrolizidine alkaloid and cause hepatogenous photosensitivity (1).
Photosensitivity of uncertain etiology includes many forage-related photosensitivities. It has been reported in cattle, sheep and horses grazing lush pasture (3). Alfalfa has been incriminated in cases of secondary photosensitization in cattle, where compromised hepatic function is not necessarily the prerequisite for the photosensitization (3).
Alsike clover is well recognized for causing photosensitization as well as oral ulcers and hepatitis. It is unclear whether the photosensitization is primarily a photodynamic agent problem or a secondary phototoxic reaction due to liver damage or whether alsike clover and its metabolites are truly the culprit (4). The photosensitization reaction could also be associated with mycotoxins produced on the plant. A similar syndrome has also been observed with horses consuming lush white clover in the fall (5).
This is what I found online...
Primary Photosensitization
Photosensitivity is commonly seen as a result of ingesting photodynamic agents from a number of plant and chemical toxins. When an animal consumes a plant or chemical containing these pigments (e.g., polyphenolic), the pigments circulate to the skin where they are exposed to UV light, fluoresce and cause oxidative injury to the cells of the skin (1). Buckwheat and St. John's wort cause primary photosensitization (1). Phosphorus fertilizer, coal tar pitch, wood preservatives, pentachloro-phenols, aflatoxin B in moldy feed, as well as a number of veterinary medicines, such as tetracycline and phenothiazine tranquilizers, can all act as photodynamic agents, absorbing the ultraviolet light and passing the energy to adjacent cells resulting in cell damage (1, 2).
Secondary Photosensitization occurs when a toxin damages the liver and results in the inability to excrete phylloerythrin. Phylloerythrin is a porphyrin compound formed by microbial degradation of chlorophyll in the gut. It is normally removed by the liver and excreted in the bile (1). If the liver is severely diseased, phylloerythrin accumulates in the blood. As it circulates through to the skin, it is exposed to UV light, fluoresces and causes oxidative injury to the blood vessels and tissues of the skin (1). Pyrrolizidine alkaloid is the most important causative agent in this group. Tansy ragwort, groundsel, fiddleneck, common heliotrope, vipers bugloss, and rattlebox contain pyrrolizidine alkaloid and cause hepatogenous photosensitivity (1).
Photosensitivity of uncertain etiology includes many forage-related photosensitivities. It has been reported in cattle, sheep and horses grazing lush pasture (3). Alfalfa has been incriminated in cases of secondary photosensitization in cattle, where compromised hepatic function is not necessarily the prerequisite for the photosensitization (3).
Alsike clover is well recognized for causing photosensitization as well as oral ulcers and hepatitis. It is unclear whether the photosensitization is primarily a photodynamic agent problem or a secondary phototoxic reaction due to liver damage or whether alsike clover and its metabolites are truly the culprit (4). The photosensitization reaction could also be associated with mycotoxins produced on the plant. A similar syndrome has also been observed with horses consuming lush white clover in the fall (5).