vitamin B-12 injection

Anybody heard of giving vitamin B-12 injection to a horse to help them gain weight? It was suggested to me today by a friend of mine for my mare. Is it ok if I do give her one? If so how many CC? Should I inject it or give it orally?
Thanks.

Injectable Vitamin B Complex (including Vitamin B12) and injectable 'Liver and Iron' (sold for baby pigs) are both great to increase appetite. We use them both all of the time when a horse is not doing well and won't eat good.

We give a mature horse 5cc of each and just squirt it in their mouth. If I did give it in a shot, I would give it IV, but it works almost as fast giving it orally.

If you give 5cc a week of each, you should see a big difference withing a couple of weeks. If you don't, then you have something bigger going on that needs to be found. A full blood panel and a really comprehensive exam would be called for.