Cattle downward hide strippers and the problem of broken backs

Summary

Over the last few years a large number of abattoirs have installed cattle hide pullers which pull the hide downwards, over the head of the carcass, which is claimed to give a better standard of dressing and require less labour then compared to the traditional upward hide puller.

When the hide is pulled over the forequarters and head the carcass is subjected to large tensile forces. To counteract these forces, it is standard practice to electrically stimulate the muscles on either side of the spine. A problem experienced by many abattoirs with the downward hide pullers is the separation of vertebrae which occurs even with electrical stimulation.

This project was undertaken to look at the variables which impact the prevalence of broken backs in carcasses then using the downward hide puller.

Objectives

The project aimed to examine the following variables impact on the prevalence of vertebrae separation associated with the use of downward hide pullers:

• the influence pf time interval between stunning and hide removal
• the effect of reduced stimulating voltage
• the influence of animal type.

Key findings

• Of 950 carcasses examined over a three day period where hides were removed by a downward pulling hide stripper, 45 carcasses were found to have a break greater than 3mm in the spinal column.
• The greatest number of breaks (29 out of the 45) were caused by a failure of the stimulation probes to make good contact with the carcass. This failure was most common in carcasses having a dressed weight greater than 300kg. This section of carcasses was predominately made up of steers, the total number of broken backs for all steers was 31.
• Where the time interval between stunning and hide stripping exceeds 35 minutes there is a greater chance of the back being broken. Reducing the stimulation voltage from 150 volts to 85 volts appears to increase the number of broken backs, but only slightly.

Benefits to industry

This project indentified the major causes of broken backs in beef carcasses when using downward hide strippers which has been identified by the Council of Australian Public Abattoir Authorities (CAPAA) engineers committee as one of two major industry problems to address (in 1976).

Once the major causes are known this will allow for solutions to be found to limit the prevalence of broken backs in beef carcasses caused by downward hide strippers and thus reduce the occurrence of downgraded carcasses due to this issue in the Australian beef industry.

MLA action

The outcomes of this project informed MLA of the major issues which caused the instances of back breakage when using the downwards hide puller and this information was disseminated to the processing industry in Australia to reduce the prevalence of this value reducing problem.

Future research

Of the 45 breaks noted during the study, 29 could be explained by the failure of the electrical stimulation probe to make correct contact with the carcass. The design of the probe used on the hide pullers during the investigations was relatively inflexible and had obvious deficiencies when a large range of animals sizes were processed. This is an obvious opportunity for future research to identify a probe design that allowed for a greater range of animal size while still successful stimulating the carcass.