BIOAVAILABILITY OF COBALT SOURCES FOR RUMINANTS .3. IN-VITRO RUMINAL PRODUCTION OF VITAMIN-B-12 AND TOTAL CORRINOIDS IN RESPONSE TO DIFFERENT COBALT SOURCES AND CONCENTRATIONS

An experiment was conducted to study production of vitamin B-12 and to tal corrinoids from different supplemental Co sources at 1 or 40 ppm d uring in vitro semicontinuous ruminal culture. Cobalt sources were rea gent grade (RG) Co sulfate, RG Co carbonate, RG Co oxide and feed grad e (FG) Co glucoheptonate. The semicontinuous culture system used a new set of in vitro tubes daily which contained substrate and 0.05 g of a control (0 added Co) or Co-containing premix. Steady state conditions for pH, total, and individual volatile fatty acids (VFA) were establi shed by day 6. Ruminal effluent was mixed and composited by tube from samples collected on days 6, 7, and 8. Production of vitamin B-12 was greater (P<0.0001) in cultures supplemented with Co sulfate, Co carbon ate, and Co glucoheptonate compared to Co oxide or the unsupplemented control. Increasing Co concentration increased (P<0.0001) concentratio n of vitamin B-12 analogues. Estimates of relative bioavailability of the Co sources based on multiple regression slope ratios of vitamin B- 12 concentration on added Co were 100, 91, 84, and 0 for Co sulfate, c arbonate, glucoheptonate, and oxide, respectively. (C) 1997 Elsevier S cience Inc.