Effect of Freezing on Fossomatic Cell Counting in Ewe Milk

Abstract

Using the Fossomatic method, a total of 10,072 analytical somatic cell count (SCC) observations were carried out on 4760 aliquots taken from 70 individual ewe milk samples with the objective of studying whether freezing showed significant differences of SCC in comparison with refrigeration, according to different analytical conditions. These conditions were four preservation procedures (without preservation, potassium dichromate, azidiol, and bronopol), two storage temperatures (refrigeration and freezing), five milk ages within storage (24h postcollection in refrigeration, and 24h, 15, 30, and 60 d postcollection in freezing), two thawing types (rapid and slow), and two analytical temperatures (40 and 60°C).Preservation, storage, and analytical temperature, type of thawing and milk age within storage, and most of the interactions showed a significant effect on the SCC variation. On average, the SCC was lower after freezing than in refrigeration. This effect depended specifically on type of preservation and analytical temperature of milk. The SCC of milk unpreserved or preserved with bronopol or potassium dichromate, and analyzed at 40°C, was not affected by freezing; however, use of azidiol as a preservative before freezing, and heating the milk to 60°C following thawing resulted in significantly decreased SCC. Milk age had little quantitative influence on SCC of thawed milk. The type of thawing (rapid and slow) did not significantly influence SCC of milk analyzed at 40°C. As a result, when using properly handled samples, the Fossomatic method could be used to enumerate SCC in samples frozen over the 60 d.