Academic article

The significance of clean and dirty animals for bacterial dynamics along the beef chain

Hauge, Sigrun J.; Nesbakken, Truls; Moen, Birgitte; Røtterud, Ole-Johan; Dommersnes, Sissel; Nesteng, Ole; Østensvik, Øyvin; Alvseike, Ole

Publication details

Journal: International journal of food microbiology, vol. 214, p. 70–76, 2015

Publisher: Elsevier

International Standard Numbers:
Printed: 0168-1605
Electronic: 1879-3460

Open Access: none


This study investigated the bacterial dynamics along the beef chain for clean and dirty cattle in the slaughter and
processing lines, using classic quantitative methods and molecular analyses. In addition, the Norwegian national
guidelines for Good Hygiene Practices inNorwaywere evaluated. In these guidelines, cattle presented for slaughter
are categorised according to hide cleanliness, resulting in separate processing lines for meat from very dirty
animals and reduced prices to farmers. The study was conducted in two commercial abattoirs in Norway. Two
groups were compared; 40 visually clean cattle and 40 visually dirty cattle presented for slaughter, with 20
from each group at each abattoir. The same animals were sampled at five sampling sites: hides, carcass surfaces
after dehiding, just before chilling, after chilling, and meat trimmings.Meat trimmings were sampled in only one
abattoir. Three hundred and sixty sampleswere collected by swabbing 100 cm2 of the brisket area at the first four
sampling sites, and sampling 200 g of meat trimmings at the fifth site. The results showed that the hides of dirty
cattle had more Enterobacteriaceae and higher Aerobic Plate Counts (APC) than visually clean cattle (P b 0.05),
however there was no significant difference for Escherichia coli. For the other sampling sites, there were no
differences between the dirty and the clean group. An effect of chilling/drying of the carcass surfaces was demonstrated
by the significant reduction in the number of carcasses on which E. coli and Enterobacteriaceae were detected;
from 11% and 39% before chilling to 1% and 16% after chilling, respectively. Enterobacteriaceae and E. coli
were detected in only three and one of the meat trimming samples, respectively. Amplification and sequencing of
the 16S rRNA gene from 643 Enterobacteriaceae colonies derived from 107 samples demonstrated that
Escherichia/Shigella were dominant within this family on the hides. However, after dehiding, after grading, and
after chilling, the genera Citrobacter and Enterobacter dominated. The meat trimmings were dominated by the
genera Kluyvera, Hafnia, and unclassified Enterobacteriaceae. The relative proportions of Escherichia/Shigella
were higher for dirty animals than for clean animals, and were higher on hides than from sampling sites further
down the chain (P b 0.05). The minor differences in contamination on carcass surfaces and meat trimmings
between clean and dirty cattle indicate that separate processing lines in Norwegian abattoirs seem to be