Short communication: Preliminary investigation into the effect of freezing and a cryopreservant on the recovery of mastitis pathogens from ewe milk

The objective of this study was to investigate the recovery of bacteria from ewe milk after freezing for 4 or 8 wk with and without the addition of glycerol as a cryopreservant. A total of 50 udder-half milk samples with a known range of bacterial species were selected, stored, and analyzed in 5 treatment groups: time zero; frozen for 4 wk with, and without, glycerol; and frozen for 8 wk with, and without, glycerol. A lower recovery was observed in all bacterial species studied after freezing. Samples containing fewer than 100 cfu/mL came from ewes with a lower somatic cell count and were more likely to be bacteriologically negative after freezing than those above this threshold. The addition of glycerol increased recovery of gram-negative bacteria after freezing, although this requires further study to draw strong conclusions. The effects on gram-positive species were inconsistent. We conclude that although the addition of glycerol had a small beneficial effect on the sensitivity of detection of bacteria from frozen sheep milk, sensitivity was highest in cultures from fresh milk.