The effect of cobalt intake on the cobamide and cobinamide composition of the rumen contents and blood plasma of sheep.

Abstract

SummaryDepending on the level of dietary cobalt, as many as nine ionophoretically distinct cobamides and cobinamides were detected in sheep rumen contents.5,6‐Dimethylbenzimidazolyl cobamide and 2‐methyladenyl cobamide together constituted more than 80% of the vitamin B12‐activity of extracts of rumen contents. The proportion of the vitamin B12‐activity due to 5,6‐dimethylbenzimidazolyl cobamide was increased from 35% to 63% by decreases in the cobalt intake from 0·34 p.p.m. to 0·04 p.p.m. but that due to 2‐methyladenyl cobamide (44%) was unaltered. Thus, a greater proportion of the “vitamin B12” synthesised in the rumen of sheep fed cobalt‐deficient rations was in a form that could be utilised by the host animal. Guanyl cobamide was occasionally present in significant concentrations at higher cobalt intakes, but the other analogues usually represented less than 3% of the total vitamin B12‐activity.Evidence was obtained that factors other than cobalt can affect both the concentrations and proportions of cobamides and cobinamides in rumen contents.The vitamin B12‐activity of extracts of sheep jugular blood plasma was almost entirely due to 5,6‐Dimethylbenzimidazolyl cobamide. 2‐Methyladenyl cobamide was present at cobalt intakes of 0·10 p.p.m. or more, but represented less than 1·5% of the total vitamin B12‐activity.