Utilization of Dietary Vitamin B12 and Cobalt by Mature Horses2

Abstract

RELATIVELY little is known about the role of vitamin B12 and cobalt in the nutrition of the equine. However, many horses in training in the United States receive daily injections of 10,000 to 20,000 µg of vitamin B12 in addition to a regular dietary source of vitamin. The National Research Council (1966) does not make a recommendation for a dietary allowance of vitamin B12. Alexander and Davies (1969) noted that horses consuming a natural diet had vitamin B12 serum levels higher than the rat and man, similar to sheep, and lower than the rabbit. Nonruminants such as rats and pigs need a dietary source of vitamin B12; whereas, rumen bacteria are capable of synthesizing adequate vitamin B12 for their host, provided adequate cobalt and phosphorus are present in the diet (Lewis, 1961). Dairy cattle have been shown to excrete 50 times more vitamin B12 than they consumed (Teeri et al., 1955) and rumen bacteria in the sheep synthesized a greater amount of vitamin B12 when consuming natural foodstuffs than when consuming semi-purified diets (Barnett and Reid, 1961).