[Ag-eq] Alfalfa hay implicated in equine photosensitivity

[Tracy Carcione]

Alfalfa Hay Implicated In Equine Photosensitivity


by Paulick Report Staff
<http://www.paulickreport.com/author/paulick-report-staff/>  | 09.19.2016 |
3:06pm 

Alfalfa hay, while a staple in many barns, may cause primary
photosensitivity in the horses that eat it, researchers from the University
of California, Davis, have found.

However, it is unclear what growing and climate conditions cause the
presence of photodynamic compounds (which cause the sensitivity) in the hay.

Photosensitization, also called photodermatitis, can occur when photoactive
substances build up in the skin and then react with sunlight. This causes an
itchy, crusty, painful dermatitis in lightly haired or unpigmented skin
(think white muzzles on horses).

Primary photosensitive reactions occur from eating the phototoxic compounds,
but secondary photosensitivity can occur when a horse's liver cannot excrete
a byproduct of chlorophyll degradation called phylloerythrin.

 

These findings were reported in The Veterinary Journal. It was noted that
for years primary photosensitization has been reported in horses that ingest
alfalfa hay. There were several large outbreaks between 2004 and 2014 in
California that researchers investigated. They collected samples of the hay
and checked for both known photosensitizing plants and pesticide residue,
but none was identified.

A feeding study was done during the 2004 outbreak, using three horses fed
only the hay suspected to have caused the outbreak. Two weeks after eating
the hay, two of the three horses developed skin lesions that were consistent
with photosensitization, suggesting that the hay was indeed responsible for
the outbreak.