Vet's View with Ravensdown Vet Gavin Goble BVSc MRCVS

Vitamin B12 is a very important vitamin for ruminants (for example, sheep and cattle) and is involved in digestion and maintaining appetite.

In these animals, vitamin B12 is manufactured in the rumen (main stomach) by micro-organisms (for example, bacteria), and requires adequate levels of dietary cobalt, because it is a central part of the vitamin B12 molecule.
Cobalt deficiency (commonly called Bush Sickness) causes vitamin B12 deficiency, of which the main symptom is ill-thrift.
Deficiency is mainly seen in weaned lambs, and less often older sheep, in parts of the country where soil cobalt levels are naturally low, such as the central plateau in the North Island. Critical levels in the diet are about 0.11 mg/kg DM (ppm) which means if the dietary level is consistently lower than this, then deficiency is likely.
Cobalt deficiency is very rarely diagnosed in cattle, especially adult cattle, because their dietary cobalt requirements are so much lower than sheep, and are usually easily supplied by the pasture.
Diagnosis and monitoring of supplementation is best achieved by herbage testing and analysis of blood and/or liver samples. The value of soil testing for cobalt is debatable.
Reference ranges for blood and liver B12 levels in sheep are well defined. Animals that are sufficient (in the normal range) will not respond, while animals that are marginal may or may not respond, to supplementation.
Prevention strategies include cobalt-amended fertilisers, pasture spraying of cobalt, cobalt boluses, vitamin B12 injections (short or long-acting) and various oral cobalt supplements.
Injectable vitamin B12, as well as treating and preventing cobalt deficiency, is also an appetite stimulant in its own right, independent of an animal's cobalt status.
This means that many responses to vitamin B12 are due to this effect, rather than remedying a deficiency, but can give rise to the mistaken belief that the animals were cobalt deficient.
I am a great fan of vitamin B12 for the appetite stimulant effect, because animals appear to visibly respond to treatment, so is useful in periods of stress.