1. The vitamin B12 in sows' milk is strongly attached to a specific ‘binder’ protein, which is present in excess. The influence of this ‘binder’ on the uptake and retention of cyanocobalamin and two natural analogues(cobinamide and Co-α-[2-methyladenyl]cobamide) was investigated with neonatal piglets.
2. Retention of a single oral dose of cyano[58Co]cobalamin given before 7 d of age was consistently higher with suckled than with early-weaned piglets, as determined by measurement of whole-body radioactivity.
3. Efficiency of retention declined with age, more rapidly in early-weaned than in suckled animals; when the dose was given at 14 d approximately 30% was retained by both groups.
4. Distribution of the retained cyano[58Co]cobalamin within the body of the piglets was the same in both groups; about half was present in the liver.
5. Foraging piglets may ingest adventitious vitamin B12 and its analogues, which are present in the sow's faeces and in contaminated litter. The influence of the vitamin B12-binder in sows' milk on the uptake and retention of two non-cobalamin analogues, and the effects of the analogues on the uptake and retention of vitamin B12 from 2 to 14 d after parturition, were investigated with early-weaned piglets.
6. The analogues were detected in the liver but not in the body organs. They were also present in blood plasma, urine and bile, in high concentration relative to that of vitamin B12. The content of analogues in the liver was very small in relation to the amounts ingested, and much less than that of vitamin B12. There was no indication that the vitamin B12-binder in sows' milk influenced uptake and retention of the analogues, or that ingestion of analogues affected the content of vitamin B12 in the body organs and fluids examined.