Effects of shearing and fleece cleanliness on microbiological contamination of lamb carcasses

The meat industry in Norway has developed national guidelines for Good Hygiene Practices for slaughtering and skinning, based on categorisation of animals. These include shearing sheep and lambs in the abattoirs immediately before slaughter. The aim of this study was to investigate microbiological carcass contamination associated with: (i) different shearing regimes; (ii) fleece cleanliness; and (iii) the slaughter process. In addition, the efficacy of the national guidelines in reducing microbial contamination was evaluated. A total of 280 swab samples were collected from the brisket areas (100 cm2) of 140 naturally contaminated lamb carcasses in a commercial abattoir. Half the samples were collected at skinning of brisket areas at the start of the slaughter-line and half of them were collected at the end of slaughter-line, just before chilling. The lambs were divided into four groups (n = 35) according to the duration of the period between shearing and slaughter: (i) 0 days (shorn at the abattoir immediately before slaughter); (ii) three days; (iii) seven days; and (iv) not shorn. Mean log colony forming units (CFU) per 100 cm2 at skinning were 5.78 and 6.95 for aerobic plate count (APC) (P < 0.05), 1.65 and 2.78 for Escherichia coli (P < 0.05) for shorn and unshorn lambs, respectively. For shorn lambs, divided according to the period between shearing and slaughter, the mean log CFU per 100 cm2 were 5.45, 5.75, 6.12 (APC) and 1.77, 1.46, 1.71 (E. coli) for the 0-days, 3-days and 7-days groups, respectively (P < 0.05 for the difference between 0- and 7-days groups in APC results). A four-category scale (0–3) was used for assessing fleece cleanliness before skinning. Visually clean lambs (score ‘0’) had lower levels of APC on the carcass surfaces than those categorised as dirty (score ‘2–3’) (P < 0.05). The carcasses at the end of the slaughter-line had lower levels of APC than they had at skinning. However, the statistical significant reduction of E. coli on carcass surfaces at skinning point for shorn lambs, were impaired and no longer significantly different from the unshorn group at the end of the slaughter-line. The increased E. coli level at the end of the slaughter-line might be explained by weaknesses related to slaughter hygiene in particular suboptimal evisceration in the abattoir which was used as a basis for our trial, and thus the national guidelines concerning shearing had not the fully intended effect on reducing microbial carcass contamination.

► Carcasses derived from shorn lambs had lower contamination of E. coli and APC than from unshorn lambs.
► The shorter time from shearing to slaughter the less contaminated were the carcasses
► Lambs with dirty fleeces had higher carcass contamination than lambs with clean fleeces.