> The vaccine is very effective when
> used according to label. Many of
> the claustridium family are
> zoonotic and therefore practically
> permanent. The one that causes the
> muscle discoloration(hence the
> name) lasts at least 10 years in
> my area, probably longer. If you
> revaccinate the cows yearly, they
> will pass significant protection
> in the colostrum to benefit the
> newborn calf.
I have been told by a vet. the Blackleg lives in the ground for 100 years. I would strongly suggest vaccinating each calf when young and then give boster at weaning. The vaccine is too cheap not to use.