an American/Californian study of course but we do tend to feed lucerne (alfalfa) here & a climate not unlike CA
Can Alfalfa Induce Type 1 Photosensitization in Horses? By Casie Bazay, NBCAAM Sep 11, 2016 Topics:
Researchers said it's still unclear if the photosensitization results from a compound in alfalfa, a compound produced by a fungus or microbe associated with alfalfa, or a compound produced in alfalfa from some type of microbial or chemical reaction.
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Alfalfa is a popular type of hay to feed horses because of its high nutritional value, but selecting this forage is not without risks. Many owners know that toxic blister beetles can contaminate alfalfa, and feeding this forage to overweight horses can cause additional problems due to its high calorie content. But in recent years, another health risk associated with alfalfa has surfaced: its apparent ability to cause photosensitization (a sensitivity to sun exposure) in horses.
To delve further into this issue, a group of researchers in California recently re-examined clinical findings from seven separate photosensitization outbreaks that occurred in California between 2004 and 2014 and involved more than 100 horses. They also referred to findings from a 2004 feeding trial performed by lead researcher, Brigit Puschner, DVM, PhD, Dipl. ABVT, professor and chair of the University of California, Davis, School of Veterinary Medicine’s Department of Molecular Biosciences. The goal was to confirm that alfalfa does, indeed, cause Type 1 photosensitization.
“Type 1 (primary) photosensitization is the result of the direct absorption of the photosensitizing agent into the blood and distribution to the skin, while Type 2 (secondary) photosensitization is the result of liver impairment,” said Puschner.
From reviewing the seven photosensitization outbreaks, the researchers found that:
All cases involved a recent diet change that included new shipments of locally harvested alfalfa hay or cubes;
Photosensitization clinical signs included crusting and itchy skin lesions on nonpigmented (pink) skin areas;
One filly died from photosensitization-related complications; and
All other horses eventually recovered with a change in diet and supportive care.
For their feeding trial, the team provided a diet comprised solely of alfalfa hay and water to three horses with varying degrees of unpigmented skin for 21 days. The horses were housed in a corral with no protection from ultraviolet exposure.
On Day 19, the team noted that two of the horses developed lesions on areas of unpigmented skin. The lesions were characterized as chronic ulcerative and necrotizing (causing cell death) dermatitis with superficial vasculitis (blood vessel inflammation), which are consistent with photosensitization. The third horse—which had no unpigmented skin—did not develop lesions, the team said.
These findings led the team to conclude that alfalfa hay can induce Type 1 photosensitization in horses. Puschner cautioned, however, that whether photosensitization results from “a compound in alfalfa, a compound produced by a fungus or microbe associated with alfalfa, or a compound produced in alfalfa from some type of microbial or chemical reaction is unknown.”
The study, “Alfalfa hay induced primary photosensitization in horses,” was published in The Veterinary Journal.
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