Microbiological assay of blood serum for the vitamin B12status of dairy cows

Abstract

SummaryFour vitamin B12assays were compared using blood sera from Friesian cows on winter diets or grazing. In herd 1, ten animals were blood-sampled three times at monthly intervals and the vitamin B12concentration of the sera determined by thePoteriochromonas malhamensisandLactobacillus delbrueckiiassays. At all three sampling dates the results produced by theP. malhamensisassay were significantly greater than those produced by theL. delbrueckiiassay. Cows in herd 2 were divided into two groups, each of 30 animals. One group was given a soluble glass bolus releasing cobalt and the other was unsupplemented. Milk yields were recorded throughout the experimental period and herbage samples were taken at intervals for cobalt determinations. Blood samples were taken at intervals from January to September 1983 and the vitamin B12concentration of the sera determined by four different assay methods: theP. malhamensisandL. delbrueckiimicrobiological assays and the Becton Dickinson and RIA Products ‘No-boil’ radioassays. The last of these failed to detect vitamin B12in any sample. There was a significant difference between the results obtained by the three other assays, with the Becton Dickinson radioassay consistently producing the lowest result and theP. malhamensisassay the highest result of the three. There was no significant effect of cobalt supplementation on milk yield.