Exsanguination (Bleed out) and shackling of cattle and sheep

The microbiological consequences of sticking are sparsely reported in the literature for both cattle and sheep.  Partly, this may be a result of the fact that sticking is a crucial part of the slaughter process and it has to proceed within 30-40 seconds of stunning to ensure that the livestock do not regain consciousness before they are fully exsanguinated.  Such an exceptionally short time scale is too small for anything other than a cursory sampling of any carcass to be made, and thus any microbiological consequences of sticking and subsequent bleed-out are presently not very well described.

There are some publications however; an early study by Mackey and Derrick reports that, although fresh mammalian blood is strongly antimicrobial because it contains antibodies, complement and leukocytes; bacterial contamination of edible tissues via blood circulation can occur if a contaminated knife is used for bleeding (Mackey and Derrick, 1979; Daly et al., 2002; Q59-Q52;Q36-Q38).  In controlled abattoir-based experiments, marker bacteria were shown to enter the circulatory system by contaminated knives as well as the central nervous system. Contamination was however, more than 10-fold less than what was recovered from the surface of cattle hides (Daly et al., 2002). 

Bell (1997) also reported that contamination of knife blades were important as a source of contamination during sticking (Q59-Q62;Q36-Q38).  Knives were however; less contaminated, by at least an order of magnitude, than the numbers of bacteria found on an operative’s hands when blades were sanitised at by immersion in water at 82oC.  As a consequence of these studies, sterilisation of knives used for bleeding has become a regulatory requirement.  The sticking stage of processing is considered to be more important than subsequent stages because immediately after stunning, a functional circulatory system still exists in the animal, and there is evidence that, despite innate immunity, this system can convey bacteria into deep muscle tissue; Bell (1997) made comment on good practices for sticking using knives. Bell believes that the knife blade used to make the initial opening cuts should by stabbed into the area of the carotid artery and any cuts that are required should be made from the inside towards the outside by running the knife blade under the skin, or alternatively by pivoting the blade against the surface being cut (Q63).

Mackey and Derrick (1979) showed that the blood and internal tissues of lambs and cattle could be contaminated during sticking.  A large inoculum (1010 – 1012 bacteria) of marked strains of E. coli, Cl. perfringens or Bacillus thuringiensis was placed on slaughter instruments before use.  Organisms from the knife for cutting the throat of sheep were isolated from the heart, lung spleen, liver and kidneys though rarely from the muscles. Marked bacteria were not detected in the bone marrow.  The numbers of marker bacteria required to demonstrate the effect are many orders of magnitude larger then those routinely encountered in slaughterhouses.  The seminal studies of Mackey and Derrick (1979) show there is a potential for contamination of offal and muscle with knife or hide surface bacteria (Q39) however the risks of such transfers occurring appears to be quite low.

Enokimoto et al. (2007) identified high incidence of Campylobacter spp. in liver (5%) and bile (45%) in healthy cattle due to transfer in the bloodstream from, it is speculated, imperfectly cleaned knives (Q59-Q62).  

Schutz (2001) also advises some good practices for sticking.  The sticking wound itself should be long enough to allow complete bleed out of the carcasses (which is a legal requirement), but a smaller wound provides less opportunity for contamination of the carcass.  Schutz (2001) also observes that carcasses should be separated after sticking in a manner such that they can't rotate and touch each other thereby preventing stick wounds from being contaminated by the dirty hooves of an adjacent carcass (Q64;Q40).

The importance of the line dragging a carcass across a floor or other surface as it is being shackled does not seem to have been published for cattle and sheep.  Although quite a hazardous undertaking, a small number samples (n=20) have been collected from a single plant in a UK plant as part of FSA study MO1045.  Near-consecutive carcasses were exclusively sponge sampled (Reid et al., 2002) at the neck and shoulder either before or after shackling in a plant where touching of these regions with the floor and guard rails was observed.  Hide contamination before and after dragging across a floor soiled with visible blood spots was assessed by comparison of log mean numbers of total aerobes (TAVC).   Mean log TAVC (n=10) before shackling were 5.6 log CFU cm-2; after dragging during shackling total aerobes rose by roughly 0.5 log CFU cm-2 to 6.1 log CFU cm-2.  The rise was significant (paired t-test; P=0.043; Q65). 

Intervention using an intravascular solution has been shown to be an effective novel intervention for reducing bacterial populations on freshly slaughtered beef carcasses (Feirtag and Pullen, 2003; Q66).  ‘Rinse & Chill’™ is an enhanced bleeding technique that involves vascular transfer of a chilled isotonic solution of approved common substances (i.e. sugars and salts) through the cardiovascular system of a beef animal during slaughtering after bleeding and shackling. The purpose of ‘Rinse & Chill’™ Technology is to lower both the muscle pH and the muscle temperature earlier and more rapidly and to more-thoroughly remove residual blood from the carcass.  In combination, these actions provide a less favourable environment for the growth and survival of bacteria.  Furthemore, the cooler carcass temperatures obtained during processing for ‘Rinse & Chill’™ carcasses allows for easier removal of hides, which may lead to less contamination on the surfaces of carcasses.  In addition, there appears to be an antimicrobial effect of the solution itself and ongoing protection against the growth of coliforms and E. coli O157:H7 in vacuum-packaged and tray packed minced beef (Feirtag and Pullen, 2003; Q66).  

References

Bell, R. G. (1997) Distribution and sources of microbial contamination on beef carcasses. Journal of Applied Microbiology 82, 292-300.

Daly, D. J., Prendergast, D. M., Sheridan, J. J., Blair, I. S. and McDowell, D. A. (2002) Use of a Marker Organism To Model the Spread of Central Nervous System Tissue in Cattle and the Abattoir Environment during Commercial Stunning and Carcass Dressing. Applied and Environmental Microbiology 68, 791-798.

Enokimoto, M., Kubo, M., Bozono, Y., Mieno, Y. and Misawa, N. (2007).  Enumeration and identification of Campylobacter species in the liver and bile of slaughtered cattle. International journal of food microbiology  118, 259-263.

Feirtag, J. M. and Pullen, M. M. (2003). A novel intervention for the reduction of bacteria on beef carcasses. Food Protection Trends 23, 558-562.

Mackey, B. M. and Derrick C. M. (1979) Contamination of deep tissues of carcasses by bacteria present on the slaughter instruments or in the gut. Journal of Applied Bacteriology 46, 355–366. (Not available electronically)

Reid, C. -A., Avery, S. M., Hutchison M. L. and Buncic, S. (2002) Evaluation of sampling methods to assess the microbiological status of cattle hides. Food Control, 13, 405-410.

Schutz, F. (1991) Analysis of slaughtering techniques- On the rail of cattle as related to hygiene requirements. Fleischwirtschaft, 3, 306-308. (Not available electronically)