Photic headshaking in the horse: 7 cases

Authors

  • J. E. MADIGAN,

    1. Department of Medicine, University of California-Davis, Davis, California 95616-8737, USA.
    2. Department of Epidemiology, University of California-Davis, Davis, California 95616-8737, USA.
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  • G. KORTZ,

    1. Department of Medicine, University of California-Davis, Davis, California 95616-8737, USA.
    2. Department of Epidemiology, University of California-Davis, Davis, California 95616-8737, USA.
    3. Department of Surgery/Radiology, University of California-Davis, Davis, California 95616-8737, USA.
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  • C. MURPHY,

    1. Department of Epidemiology, University of California-Davis, Davis, California 95616-8737, USA.
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    • School of Veterinary Medicine, Department of Medical Sciences, 2015 Linden Drive, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.

  • LYNN RODGER

    1. Department of Epidemiology, University of California-Davis, Davis, California 95616-8737, USA.
    2. Veterinary Medical Teaching Hospital, School of Veterinary Medicine, University of California-Davis, Davis, California 95616-8737, USA.
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Summary

Seven horses with headshaking are described. No physical abnormalities were detected in any of the cases. Six of these horses had onset of clinical signs in the spring. The role of light was assessed by application of a blindfold or dark grey lens to the eyes, covering the eyes with a face mask and observing the horse in total darkness outdoors. Cessation of headshaking was observed with blindfolding (5/5 horses), night darkness outdoors (4/4 horses) and use of grey lenses (2/3 horses). Outdoor behaviour suggested efforts to avoid light in 4/4 cases. The photic sneeze in man is suggested as a putative mechanism for equine headshaking. Five of 7 horses had improvement with cyproheptadine treatment (0.3 mg/kg bwt b.i.d.). Headshaking developed within 2 calendar weeks of the same date for 3 consecutive years in one horse. Neuropharmacological alterations associated with photoperiod mechanisms leading to optic trigeminal summation are suggested as possible reasons for spring onset of headshaking.

Ancillary