Viable Cells in Bovine Milk

Abstract

SUMMARY A simple and rapid method is described for differentiating between viable and dead somatic cells in milk with the trypan blue stain. Dead cells were stained blue, whereas the viable cells were not stained and appeared as colourless, refractile round objects containing nuclei. The percentage of viable cells in foremilk and strippings was similar and not necessarily related to the number of cells per millilitre of milk. Thus the absolute number of viable cells generally varied directly with the total cell count. Milk samples yielding no bacterial growth contained on an average a slightly lower percentage of viable cells than milk samples having 100 to 10,000 or more bacteria per millilitre. Both the number and the percentage of viable cells increased during the acute phase of experimental mastitis induced with sterilized distilled water or 0·85 per cent NaCl solution. The proportion of viable cells gradually decreased when milk was stored at 4 c for several days.