What blood work has been done? has a B12/Folate test been done (think called a TLI)....this would be looking for EPI....check out site epi4dogs (google) to find similar...sometimes the test will be normal as folate can mask a b12 defciency.
what do you feed?
If you are going to give b/12 make sure it is methylcobalamin, not the cyano version (synthetic)...and should be w/folate...
Also, provided tests show deficiency, if b12 isn't being utilized, this may be do to a lack of intrinsic factor w/o it b12 is not utilized....metagenics makes a b12 suppl. w/intrinsic factor....it's that or injections.
you can also look into SeaCure...this is used in cases of wasting...
Another product is called SeaVite which is combo of seacure and colostrum - look up here, the benefits of both...
Proper Nutrition: SeaVive® - Comprehensive Immune Support
Seacure for Pets 100g powder by Proper Nutrition
Hope this helps