Plasma and liver vitamin B12 concentrations in cattle.

Abstract

Proc. Aust. Soc. Anim. Prod. Vol. 19 PLASMA AND LIVER VITAMIN B12 CONCENTRATIONS IN CATTLE W. J. BABIDGE Waite Agricultural Research Institute, University of Adelaide, S.A. 500 1. Plasma vitamin Bi2 has been used in sheep to assess current cobalt intake, although it cannot be used to predict liver B12 reserves (Sutherland 1980; Millar and Albyt 1984). In cattle, few data are available regarding plasma B12 concentrations as indicators of B12 status. The aim of this study was to examine the relationship between plasma and liver B12 concentrations in cattle. Hereford cross heifers of about 4 months of age were housed in individual pens and fed a diet of pelleted hay and barley (50:50, cobalt 0.04 mg/kg DM). Animals were allocated to one of 3 treatment groups (5 per group) based on liveweight and liver Bi2 concentration. The treatments were: Control (no added cobalt) Supplemented (0.5 mg cobalt daily) pair-fed to control Supplemented, with ad Zibitum diet Samples of blood and liver were taken at intervals over an 8-month period. Vitamin B12 in blood and liver was determined using a radioisotope dilution method (Judson et aZ. 1988). There was no difference in feed intakes or liveweights (mean increase 420 g/day) between groups during the experimental period. Fig. 1. Liver (H, nmolkg) and plasma (0, pmol/L) vitamin B12 concentrations in cattle fed diets without cobalt supplement (control) or supplemented and either pair-fed to control or fed ud Zibitum. Analysis of variance showed a time x treatment interaction (P < 0.05) for plasma Br2 and a time effect (P c 0.001) for liver B12. Tukey' test indicated that mean plasma Bi2 of pair-fed animals was s significantly greater (P < 0.05) than controls at week 32. Regression analysis demonstrated a parallel response in the pair-fed (P <O.OOl) and ad Zibitum (P < 0.001) animals for liver and plasma B12 but different intercepts and slopes (P < 0.001) for the control animals. Plasma B12 in cattle was not very responsive to cobalt supplementation but increased at the sarne rate as liver B12 (Fig. 1). Clarke et al. (1986) found similar trends in cattle at pasture with adequate liver Bi2. In controls there was no relationship between the 2 variables. These results cast doubt on plasma B12 as a reliable guide to cobalt intake in cattle. It also appears that 0.04 mg/kg cobalt in the diet was not sufficiently low to induce a clinical B 1 2 deficiency. CLARKE, R. G., ELLISON, R. S., KIRK, J. A., MORTLEMAN, L., WILLIAMSON, L. and HENDERSON, H. V. ( 1986). N.Z. J. Agric. Res. 29: 443-8. JUDSON, G. J., SHALLOW, M. and ELLIS, N. J. S. (1988). Proc. N.Z. trace elements group conference, Canterbury 225-9. MILLAR, K. R. and ALBYT, A. T. (1984). N.Z. Vet. J. 32: 105-8. SUTHERLAND, R. J.(1980). N.Z. Vet. J. 28: 169-70. 388