Alice M. Doherty - The National Food Centre
The microflora and cleanliness of beef hide are considered to have a major influence on the contamination of carcasses during slaughter. Transfer of contamination from the hide to the carcass is unavoidable due to the nature of hide removal. Contamination can occur by direct contact between the hide and the carcass, or by contact between the carcass and operatives hands, clothes, tools or factory equipment that had previously been in contact with the hide. Micro-organisms present on the hide are derived from faeces, soil, water and vegetation and can include pathogens such as Escherichia coli 0157:H7 and Salmonella.
The hide of cattle presented for slaughter can, at times, be excessively dirty due to adherent dirt, faeces and straw. Hide cleanliness can be improved in a number of ways such as controlling diet and feeding before slaughter, optimising housing conditions so that there is minimal soiling of the hide, and transporting the animals to the abattoir under suitable conditions. Animals may also be clipped prior to slaughter to remove physical soiling, though this procedure can be dangerous for operatives and it is essential that it is undertaken using the correct handling facilities. The presentation of dirty cattle for slaughter is expensive for the farmer and the beef industry. Animals rejected for slaughter due to excessive levels of dirt may be returned to the farm of origin resulting in increased transport costs. Alternatively, animals may be clipped in the abattoir, or slaughtered at the end of the day. This will result in increased expenses due to additional lairage costs, bedding, labour etc. Dirty hides are also less valuable than clean hides. Carcasses contaminated by excessively dirty hides will require additional trimming thus reducing carcass weights.
Regulations relating to excessively dirty cattle are in place in a number of countries. Special hide regulations were adopted in 1982 in Finland for economic and animal welfare reasons. The Australian Meat Safety Enhancement Program restricts the slaughter of excessively dirty cattle and educates cattle producers on the importance of clean livestock through its Cattlecare programme. The United States Pathogen Reduction Hazard Analysis Critical Control Point (HACCP) system and the Canadian Food Safety Enhancement Program do not address the issue of clean cattle. However, some abattoirs in North America and Canada do adjust their practices in accordance with the hide status of the cattle. In the United Kingdom, the Meat Hygiene Service have a policy of rejecting excessively dirty cattle due to the perceived extra risk of cross contamination during dressing operations.
The Irish Department of Agriculture and Food introduced regulations in 1998 to address the issue of excessively dirty cattle at the abattoir. These regulations allow the ante-mortem veterinary inspector to reject animals for slaughter or to permit slaughter under special conditions. On the basis of pictorial and written guidelines, cattle are placed in categories from 1 (very clean) to 5 (very dirty). Normal dressing procedures are employed for categories 1 and 2, with extra care being taken for animals with wet hides. Slowing of the line speed, reduced numbers of carcasses on the line and improved workstation hygiene are considered for category 3 animals. Category 4 animals are slaughtered under similar special conditions at the end of the day and category 5 animals are rejected for slaughter.
Irish Department of Agriculture and Food, Livestock Cleanliness Categories
Category 1:
No evidence of adherent faecal material and very limited amounts of loose straw/bedding.
Category 2:
A light covering of dried faecal material and limited amounts of loosely adherent straw/bedding.
Category 3:
Animals with significant amounts of straw/bedding/dirt over large areas of predilection sites.
Category 4:
Animals with heavy amounts of adherent dirt/faeces on fore and hind legs and/or on predilection sites and/or significant amounts of straw/bedding attached to the hide or between areas of dried faecal material. Hide clipping may be practiced before animals are permitted for slaughter.
Category 5:
Animals with very heavy amounts of adherent dirt/faeces on predilection sites. Balling of adherent dirt/faeces may be evident on the underside of the abdomen. Animals are rejected for slaughter and returned to the premises of origin or subjected to hide clipping.
During the implementation of the regulations in Ireland, a study was conducted at The National Food Centre to examine the relationship between hide cleanliness and carcass contamination. Animals from clean and dirty categories were slaughtered and contamination levels were determined at five sites (hock, brisket, cranial back, bung and inside round) on the subsequent carcasses. The results showed increased contamination levels on carcasses from dirty animals, at the hock and brisket sites on the carcass. Similarly, a study in Finland reported that briskets from excessively dungy cattle were significantly more contaminated than briskets from normal cattle. Individual carcasses were used to assess the effect of hide cleanliness on carcass contamination in the studies at The National Food Centre and in Finland. Using carcasses from lots of cattle, a Canadian study did not find a positive relationship between tag (mud, bedding and manure) on hide (belly, leg and side) and carcass contamination. In the Canadian study, bacterial numbers and tag scores were averaged for twelve carcasses in a lot. It is possible that pooling of the samples in this manner may have masked individual relationships. For example, positive and negative relationships were recorded between bacterial counts on carcasses and lot side scores/lot belly scores under certain conditions.
There were no differences between clean and dirty animals at the bung, cranial back and inside round sites of the carcass in the study at The National Food Centre. The result for the bung is surprising given that it was handled during hide removal and is considered to be a possible site of direct/indirect faecal contamination. The cranial back and inside round were not contacted by the outer surface of the hide and the cranial back was also not subjected to manual skinning. The inside round was examined after trimming and so any contamination present may have been reduced or removed by this action. It is reasonable to attribute contamination at these sites to background microflora from the processing environment and aerial contaminants.
The brisket was identified as the most contaminated of the five sites examined in the study at The National Food Centre, followed by the hock. The hock was sampled at first legging after loosening of the hide from the hind legs and the brisket was sampled after hide removal. The hock and brisket are generally considered to be important sites of increased contamination after hide removal. The extent of contamination at these sites is influenced by the level of manual skinning required at hide removal, the skill of the operative and the hygiene of abattoirs. Changes in personnel between sampling days and the effect of their actions would also be expected to influence carcass contamination. Variation between personnel is difficult to control under commercial conditions.
It is well recognised that operatives' hands are a source of contamination from the hide or fleece of animals to carcasses. The extent of carcass contamination can be reduced at hide removal through the provision of clean gloves, sterile knives and steels for operatives employed at this stage of dressing. Under commercial slaughter conditions, it would be impractical for operatives to change their gloves between carcasses. However, the sterilisation of knives and steels could be done in the factory through the proper use of sterilisers situated along the slaughter line. After treatment with water at 82°C, the risk of contamination from the knife blade used for the initial incision on the hide is considered to be negligible. It is also generally assumed that slowing of the line speed, allowing for greater care during slaughter, will result in reduced carcass contamination, though this is not always the case. The relationship between line speed and carcass contamination is complicated by a number of different factors such as operative fatigue, knife skills, length of working day, levels of boredom, the proper use of a HACCP system and the time allocated for the operatives to do their jobs.
In conclusion, the slaughter of cattle with excessively dirty hides will result in increased bacterial contamination at certain sites on the carcass. The extent of this contamination at hide removal can however be reduced using improved hygienic practices.
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