Thanks, I'm well aware of the feeding risks. I've done a lot of Internet research on that and the concensus is: nobody at any public research institution has done work to figure out exactly when you should/should not feed vetch.  Older cattle are more susceptible than young, and feeding vetch once it has seed should be avoided, but nothing has been figured out beyond those general recommendations.

Some people have grazed vetch & oats for years with no known problems. Some sheep people apparently use vetch quite a bit--you'll find several Web pages about vetch hay & grazing from Australia. Maybe the people who have had cattle die from it fed vetch that had some maturing seed? Nobody really knows.

Looks like feeding it to younger stock, diluted with other feed/grass and not fed for an extended period of time, is not very risky.