Vitamin B12 requirements are exceedingly small; an adequate allowance is only a few mg per kg of feed. Swine requirements vary from 5 to 20 µg per kg (2.3 to 9.1 µg per lb) of feed (NRC, 1998), with young pigs and breeding animals having the highest requirement. Early on, Anderson and Hogan (1950) suggested inclusion of orally administered vitamin B12 at the rate of 0.26 µg daily per kg of live weight, or not over 1.5 µg per 100 g of feed. Johnson et al. (1949) estimated the oral vitamin B12 requirement of the baby pig to be approximately 20 µg per kg of dry matter consumed, or 0.6 µg B12 per kg body weight daily when provided by injection. After monitoring growth performance in pigs supplied with 0, 17, 34, 51, or 68 µg of a vitamin B12 concentrate per kg dry matter, Neumann et al. (1950) estimated the vitamin B12 requirement to be approximately 50 µg of activity per kg of diet. The vitamin B12 requirements of various species depend on the levels of several other nutrients in the diet. Excessive protein increases the need for vitamin B12, as does performance level. The vitamin B12 requirement seems to depend on the levels of choline, methionine and folic acid in the diet; vitamin B12 is also interrelated with ascorbic acid metabolism (Scott et al., 1982). The requirements for both vitamin B12 and folic acid are reduced when the diet contains an abundance of compounds that can supply methyl groups (Dyer et al., 1949). Sewell et al. (1952) showed that vitamin B12 has a sparing effect on the methionine needs of the pig. A reciprocal relationship occurs between vitamin B12 and pantothenic acid in chick nutrition, with pantothenic acid having a sparing effect on the vitamin B12 requirement. However, Luecke et al. (1952) did not observe a sparing effect of vitamin B12 on the pantothenic acid requirement of the pig. Luecke et al. (1952) indicated that the addition of 25 µg of vitamin B12 per pound of feed may not have been sufficient to demonstrate a relationship between vitamin B12 and pantothenic acid. Dietary ingredients may also affect the requirement, as wheat bran has been shown to reduce availability of vitamin B12 in humans (Lewis et al., 1986).
Colby and Ensminger (1950) were unable to detect a benefit of supplemental vitamin B12 when fed to growing pigs. However, Colby and Ensminger (1950) suggested that the experimental ration may not have been entirely free of the vitamin; intestinal synthesis may have occurred; or sufficient storage by the pigs from previous sources may have been involved in the lack of detection of a growth response that was different from that of the control animals. Bryant et al. (1981) reported that supplementation of a corn-soybean meal diet with 22 µg per kg vitamin B12 increased daily gains of both barrows and gilts by 6%, but this increase was not statistically significant. Dietary need for vitamin B12 depends on intestinal synthesis in addition to tissue reserves at birth. In order to study the vitamin B12 needs of the young pig without prior accumulation of the vitamin, Bauriedel et al. (1954) utilized purified diets and baby pigs that were not allowed to suckle. It was reported that baby pigs can be raised from birth on purified diets and that a marked depletion of vitamin B12 could occur within 8 weeks. Early research findings (Richardson et al., 1951) suggested that when the intestinal flora is controlled through antibiotics administration, the vitamin B12 requirement of the weanling pigs is 5 µg or less per lb of ration. When antibiotics and vitamin B12 were added to a corn-soybean meal diet, growth and feed efficiency were increased. Richardson et al. (1951) suggested that the antibiotics (10 mg each of Aureomycin hydrochloride, streptomycin sulfate, terramycin hydrochloride and procaine penicillin G) adversely affected the intestinal flora, allowing more of the vitamin B12 supplemented in the ration to be available for the pig. Intestinal synthesis probably explains frequent failures to produce a vitamin B12 deficiency in pigs and rats on diets designed to be vitamin B12-free. The deficiency can be readily produced in rats, however, when coprophagy is prevented completely (Barnes and Fiala, 1958). Coprophagous animals on deep litter receive excellent sources of vitamin B12 from microbial fermentation. The pig's inclination toward coprophagy will supply part of the vitamin B12 requirement. Swine also obtain some vitamin B12 by direct absorption of the vitamin produced by bacterial synthesis in the intestine (NRC, 1998). However, the amount from this source is not reliable. Hendricks et al. (1964) investigated the absorption of vitamin B12 from the colon of young pigs. The authors concluded that 41.6% to 58% of vitamin B12 labeled with cobalt-57 was absorbed from the colon. Hendricks et al. (1964) also reported that some vitamin B12 appeared to be metabolized during its passage through the lower digestive tract.
