Microbiological contamination of ovine carcasses associated with the presence of wool and faecal material.

Abstract

The microbiological contamination of ovine hind legs at sites which were visibly clean (control carcasses), sites immediately adjacent to and below visually contaminated sites, and sites contaminated with visible faecal material or wool were determined by excision sampling immediately after pelting and immediately after a pre-evisceration wash. The mean aerobic plate count (APC) and Escherichia coli count (EC) at clean sites immediately after pelting ranged from log10 cm-2 3.98 to 4.44 and log10 cm-2 0.96 to 1.51, respectively. These levels of contamination were significantly lower than those on sites contaminated with faecal material (log10 cm-2 6.00 and 3.00, respectively) or wool (log10 cm-2 5.44 and 2.45, respectively). The presence of faecal material or wool on the carcass was not associated with increased bacterial numbers on visually clean areas of the carcass. This indicates that the presence of faecal material or wool alone cannot be used as an indicator of the hygienic status of the carcass as a whole, particularly in the role of on-line monitoring parameters for HACCP systems. Pre-evisceration washing of carcasses had very little effect on the uncontaminated areas of the carcasses, but reduced the mean APC and EC at the site of visible contaminants. There was little evidence of redistribution of bacteria to immediately adjacent but visually clean sites. However, the residual levels of both APCs and ECs directly at sites of faecal contamination after washing were still significantly higher than at visually clean sites. Application of HACCP principles to ovine slaughter and dressing suggests that visible faecal material should be removed by trimming, whereas pre-evisceration washes can have a practical and microbiologically validated role in the removal of wool. There was generally a good correlation between APCs and ECs at the uncontaminated sites prior to pre-evisceration washing, suggesting that in some situations APCs can act as a useful indicator of both general carcass hygiene and the presence of faecal indicators.