In recent years, another health risk associated with alfalfa has surfaced: its apparent ability to cause photosensitization (a sensitivity to sun exposure) in horses. | Photo: iStock

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