Vitamin B12 levels in ewe colostrum and milk and in lamb serum.

Vitamin B12 was measured in samples of normal ovine colostrum and milk and in sera of lambs and ewes taken at various stages of lactation, from lambing up to 16 d. Colostrum obtained within 24 h of lambing contained high concentrations of vitamin B12, but within a few days the levels fell. The lambs received high levels of vitamin B12 from their dams' colostrum but a parallel decrease of vitamin B12 levels in lambs' serum and ewes' milk was subsequently observed. Milk vitamin B12 was analysed by the microbiological method (Lactobacillus leichmannii, ATCC 7830) and a radioisotope dilution (RID) technique. Milk vitamin B12 concentrations were greater with the microbiological technique compared with the RID method. The radioassay method has been shown to be as reliable as the microbiological method for measuring vitamin B12 in ovine milk except for very low levels.