Vitamin B12 is produced by fermentation and is available commercially as cyanocobalamin for addition to feed. Vitamin B12 is only slightly sensitive to heat, oxygen, moisture and light (Gadient, 1986). Verbeeck (1975) reported vitamin B12 to have good stability in premixes with or without minerals, regardless of the source of the minerals. Scott (1966) indicated that there is apparently little effect of pelleting on vitamin B12 content of feed.
Results of a large number of animal experiments are about equally divided between those reporting a positive response to dietary cyanocobalamin supplementation and those reporting little or no response. Variable responses may be due to several factors: initial body stores, environmental sources of the vitamin (such as molds, soil and animal excreta), microbial synthesis in the intestinal tract and adequacy or deficiency of other nutrients that influence B12 requirements.
The use of commercially available feeds for dogs and cats would normally provide sufficient amounts of dietary vitamin B12 to meet their requirements. Cats should receive ample vitamin B12 through fish products, which are rich in the vitamin. Dogs practicing coprophagy would receive a rich source of the vitamin. Special supplementation of vitamin B12 would be needed for dogs and cats suspected or known to have genetic defects in the metabolism of the vitamin. Pancreas insufficiency would warrant B12 supplementation since this would be an important cause of vitamin B12 malabsorption in dogs; this is the main source of intrinsic factor in this species. Dogs in heavy training need ample amounts of vitamin B12 to facilitate erythrocyte development and, in turn, increase the oxygen-carrying capacity of the blood. Some sled dogs reportedly have been injected with vitamin B12 several days before racing to increase plasma levels of erythrocytes (Corbin and Kronfeld, 1972).
