Warning signs include persistent fatigue despite adequate sleep, cold intolerance (especially cold hands and feet), menstrual irregularity or cessation in female subjects, hair thinning or shedding, and mood disturbances (irritability, low motivation)
By the time it's recognized that you have B12 deficiency, you probably only realize your levels are lower now than they've been for some time now
S2CID 28557054
On my farm, we keep a multi-species B12 solution on hand that can be administered to any species of livestock we have on the farm (we raise sheep, chickens, and pigs, but the solution could also be used for goats and cattle or even domesticated pets)
Eating smaller, more frequent meals also helps, as does staying well hydrated