A study of methods for estimating the cell content of bulk milk

Teat diameter gradient associated with milk yield and somatic cell count in British Friesian cows

Teat diameters of 144 British Friesian cows were measured (1) at the proximal end of the teat and (2) 20 mm above the distal end before and after milking. Proximal minus distal diameter—‘teat diameter gradient’is used to describe shapes varying from cylindrical to funnel-shaped. Proximal and distal teat diameters and teat diameter gradient had higher values before milking than after milking. Teat diameter, teat diameter gradient and difference in gradient before and after milking, were positively correlated with milk yield and negatively correlated with somatic cell count.

Effect of storage on the electronic cell count of milk

Using a standard method, the electronic cell count of formalin-treated milk usually increased during storage. This increase varied with the milk and was found to be due to a corresponding decrease in the effectiveness of the fat-dispersal procedure before counting. A more severe fat-dispersal procedure incorporated into the standard method resulted in a stable cell count being obtained. It was found that formalin must be added to milk within 24 h of milking to prevent lysis of the cells.

Reproducibility of the electronic cell-count procedure for counting somatic cells in milk

A series of experiments is described, outlining a study of 5 factors likely to influence the efficiency and reproducibility of a standardized method used for the electronic counting of somatic cells in milk. Samples containing cells covering 5 ranges from 250000 cells/ml to 1500000 cells/ml were used and the results analysed statistically.

The residual error was given special consideration, and was found not to contribute to any significant degree to the accuracy of the method. Sample volumes of 0·5 ml and 0·1 ml used for counting were compared, and there was a decrease in accuracy using the smaller volume. The influence of individual technician skill was studied with 4 workers having differing degrees of experience, and no significant addition to the overall error was observed. The effect of agitating bulk tank milk for between 0 and 2 min before sampling was examined. Variations were considerable for agitation times of less than 1 min, but the recommended mixing time of 2 min was found to be adequate with milk quantities between 450 l and 2250 l (100 and 500 gal), and at the 5 cell-count levels chosen.

The distributions of the cell counts at the 5 levels were found to be normal with the marginal exception of samples tested at 250000 cells/ml.

All aspects of the technique, sample preparation, use and calibration of the Coulter Counter, etc, should be closely followed to ensure that no inaccuracies will result from inadequate maintenance of the machine or other equipment employed in the test.

Cell volume to aid analysis and technique of somatic cell counts in milk

In conjunction with a Coulter Counter, somatic cells in milk were sized by electronic analysis. Quarter milk from cows with mastitis had a cell volume peak with a modal cell volume of 102 mu3 while milk from healthy quarters had no peak. Bulk milks with a peak had higher cell counts than milks where there was no peak. Dimensions of peak from bulk milks were the same as from quarter milks. Modal cell volume and cell count varied after milks were fixed with varying concentrations and types of fixative. The concentration of fixative recommended by the International Dairy Federation was sufficient, but only marginally so, and it should be increased.