1. Teddy Lancaster suggested it was black walnut poisoning in the bedding.
I was surprised at first because I always ask at the mill and I had five
horses on the same bedding and this one was the only one who reacted. But,
so be safe, I had the stalls stripped. When we went back to the mill for
more sawdust, we asked and they said, "Oh yes. We've been sawing a lot of
black walnut!" When I ran this by my vet to see if she thought we should
be treating him differently, she said she had had another case of black
walnut poisoning but this horse had colicked--mine had not.
It turns out that the "trusted" mill in our area (the one where we alwasy
ask if ther's black walnut in it and there never has been) has gone out of
business and all the horse people are now purchasing bedding at the other
high profile mill, but the communication link is not working so horse
owners are getting black walnut. We've been warning horse owners in the
area now to be sure to check.
After about 2.5 weeks of swollen legs that went down with 30cc of
penecillin twice daily and mild exercise, I eased the horse back into his
exercise routine. The swelling seemed to diminish with exercise, but
popped back up again with confinement. The horse went to a 2 day 55 miler
last weekend, and I presented the situation to the ride vet who thought the
horse would be OK and suggested going ahead with the exercise. At check in
there was fill in all four legs and heat in two fetlocks. I was worried.
Nevertheless, after 1/2 hour of riding, all swelling was gone and the vet
said to keep going. The horse finished sound, and had no metabolic
problems. Moving over the miles helped to flush out the remaining poison.
Barb Peck also described a similar mysterious incident and one of the
suspect agents in her case was black walnut poisoning. Other suggestions
were that biting ants or ground bees had been the cause. And noxious
plants of some sort were also suggested--especially with the possibility
that a dry summer or a wet one might have changed the level of toxicity in
some plants enough to cause this reaction.
I guess I've settled on the black walnut poisoning theory given the other
information I have, though there might still have been some influence from
one of the other sources operating simultaneously.
Some info in case someone else runs into this: My vet says that it is
highly unpredictable which horses will show allergic reactions to black
walnut poisoning, and the severity of the reaction is variable too, ranging
from swelling to colic to death. Treatment seems to be removal from the
offending bedding, 30cc of penecillin 2x a day.
I feel blessed that swelling was all my horse had to suffer, and I will
indeed protect him more by asking more regularly what had been sawed
recently at the mill.
Thanks for your input, and it really helped to have fellow horse-people out
there to ease the fear and help find the cause.