Effect of pre-slaughter washing of lambs on the microbiological and visible contamination of the carcases.

Studies in four slaughterhouses with contrasting dressing systems showed that microbiological contamination with total aerobic bacteria and Escherichia coli was greater on carcases which had been washed before slaughter, irrespective of wool length, and was generally higher on carcases derived from woolly lambs than on those derived from shorn lambs. The effects of pre-slaughter washing on the forequarters compared with the hindquarters were not consistent, and this was attributed to differences between the dressing systems applied in the slaughterhouses. Over all trials the mean total aerobic count ranged from 3.45 to 5.36 log10/cm2, and the mean counts of E coli ranged from 0.39 to 2.11 log10/cm2. There was less visible contamination on the carcases of washed lambs than on those of unwashed lambs. The differences in contamination with wool were largely dependent on the level of contamination of individual carcases, whereas the differences in contamination with faecal material and dirt or sand were largely dependent on the prevalence of affected carcases. The use of pre-slaughter washing to compensate in visual terms for poor pre-slaughter presentation results in a detrimental effect on microbiological loads on ovine carcases.