Polyneuropathy associated with forage sources in Norwegian horses.
BACKGROUND
Cases of hindlimb digital extensor weakness of unknown etiology have been observed in Norway since 1995.


OBJECTIVE
We hypothesized that the observed bilateral extensor weakness was attributable to neuropathy of the distal nerves and that this was related to environmental factors, possibly dietary.


METHODS
Seventy-five horses with digital extensor weakness occurring from 1995 to 2004 are described.


METHODS
Eleven horses were examined at The Norwegian School of Veterinary Science, and the medical records of 64 horses seen in ambulatory practice were reviewed.


RESULTS
There was no apparent sex, age, or breed predilection, but the majority were horses kept for pleasure or breeding purposes. Clinical signs varied from intermittent knuckling of the hindlimbs to paraplegia. Some horses showed no or only slow progression of signs, whereas others developed severe signs within hours. No other neurologic deficits were detected in any of the horses. Epidemiologic data and laboratory results were not supportive of an infectious etiology. The only common factor for all affected horses seemed to be feeding big bale silage or, occasionally, hay of poor microbiologic quality. Forty of the 75 horses were euthanized. Histopathologic examination of peripheral nervous tissue was performed in 22 horses, all of which had neuronal fiber degeneration. The majority of horses with mild signs recovered after 5-6 months of rest.


CONCLUSIONS
Clinical signs correlated with polyneuropathy involving sciatic nerves.
Hanche-Olsen
S
S
Department of Companion Animal Clinical Sciences, Equine Section, Norwegian School of Veterinary Science, Oslo, Norway. siv.h.olsen@veths.no
Teige
J
J
Skaar
I
I
Ihler
C F
CF
D000821:Animal Feed / Q000009:adverse effects*; D000818:Animals; D005260:Female; D006614:Hindlimb; D006734:Horse Diseases / Q000453:epidemiology / Q000209:etiology* / Q000473:pathology; D006736:Horses; D008297:Male; D009186:Myelin Sheath / Q000473:pathology; D009664:Norway / Q000453:epidemiology; D006109:Poaceae / Q000009:adverse effects; D011115:Polyneuropathies / Q000453:epidemiology / Q000209:etiology / Q000473:pathology / Q000662:veterinary*; D012189:Retrospective Studies; D012820:Silage / Q000009:adverse effects; D013997:Time Factors