It won't hurt anything - but unlikely to help or even be necessary. B12 deficiency is exceedingly rare in cattle; so long as their diet contains trace amounts of cobalt(like 0.1ppm), the rumen microbes can synthesize it. B12 deficiency can be a problem in pre-ruminant calves, or cattle that are off feed - but I'd hazard a guess that most B12 that's given to cattle is totally unnecessary.