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Nowadays, estimates of dietary vitamin B12 requirements in postweaning pigs are based on studies carried out before 1966 and vary from 15 to 20 μg/kg. However, typical amounts used by the feed industry range between 20 and 30 μg/kg. For this reason, the objective of this study was to estimate the bioavailability of dietary vitamin B12 to know the reliable estimation of the most suitable dietary allowance of vitamin B12.
In the present study, 2 approaches were used to determine bioavailability of 2 quantities of dietary cyanocobalamin in growing pigs. In the first trial, 15 blocks of 3 pigs (31.7 ± 0.5 kg of BW) were formed according to their vitamin B12 status. Within each block, 1 pig (CONT) was killed and tissues were sampled for vitamin B12 determination. The remaining 2 piglets were fed 25 (B12-25) or 250 (B12-250) μg daily of cyanocobalamin for 8 d. Urine was sampled twice daily, and the pigs were killed and sampled as CONT pigs. The total content of vitamin B12 in the carcass, urine, and intestinal tract was affected by the dietary treatments (P < 0.01) but not in the liver (P > 0.019). The whole body retention of vitamin B12 was greater (P = 0.02) in B12-250 than B12-25 pigs, but the corresponding bioavailability was estimated to be 5.3 and 38.2%, respectively. In trial 2, 11 pigs (35.1 ± 4.0 kg of BW) fed a diet unsupplemented with vitamin B12, from weaning at 28 d of age, were surgically equipped with catheters in the portal vein and carotid artery, and an ultrasonic flow probe around the portal vein. Each pig received 3 boluses of 0 (B12-0), 25, and 250 μg of dietary vitamin B12 according to a crossover design.
Postprandial nycthemeral arterial plasma concentrations of vitamin B12 reached minimum values (P < 0.01) between 15 and 18 h postmeal that were 29.6, 15.6, and 10.0% less than the premeal values for B12-0, B12-25, and B12-250 pigs, respectively (linear, P < 0.01). The cumulative net flux of vitamin B12 for 24 h corresponded to 2.4 and 5.1 μg for B12-25 and B12-250 treatments, respectively, and the corresponding bioavailability was estimated to be 9.7 and 2.0%, respectively.
As a result, a daily dietary supplementation of 25 μg, which is greater than NRC (1998) recommendation (15 μg/kg) but similar to the level commonly used by the industry, seemed adequate to maximize vitamin B12 in liver (trial 1) and to attenuate the nycthemeral decrease in arterial plasma concentrations of vitamin B12 (trial 2). Although the bioavailability of vitamin B12 was apparently substantially decreased with a daily dietary supplementation with 250 μg, such a supplement could build up whole body reserves (carcass and digestive tract) by up to 40% (trial 1) or doubled the cumulative net flux of the vitamin across portal-drained viscera (trial 2) over a supplementation with 25 μg.
J J Matte, F Guay, N Le Floc'h and CL Girard, 2010. Journal of Animal Science, 88:3936-3944. http://dx.doi.org/10.2527/jas.2010-2979