Pig stress that occurs in connection with slaughtering can affect the metabolism in muscle cells, which in turn can have impact on meat quality, reports the University of Aarhus.

When pigs are stressed in connection with the slaughtering process, it can affect meat quality. Scientists from the Faculty of Agricultural Sciences have identified metabolites that could potentially be used as markers for slaughter stress.

A pig's last hours can be a rather stressful time. The pig finds itself in strange surroundings, it meets strange pigs, goes for a drive, and is then herded into an abattoir. Stress in a pig destined for slaughter can affect its meat quality. That is not news in itself, but the effect on the cellular level has not been revealed – at least not until now.

Postdoc Ida Krestine Straadt from the Faculty of Agricultural Sciences at Aarhus University has identified metabolites that can potentially be used as markers for the stress effects that occur in connection with slaughtering.

She cultured muscle cells in the laboratory under conditions that correspond to the stress situations to which a finisher pig is subjected.. She subjected the cells to heat or to lack of oxygen. Heat stress can occur in connection with transportation and handling of pigs while lack of oxygen can arise in connection with sedation prior to slaughter.

Dr Straadt explained: "My studies showed that changes occur in the metabolites when there is heat stress or lack of oxygen in cultured muscle cells."

She found a decrease in the amino acids alanine, glutamate, glutamine, aspartate and phenylalanine with heat and oxygen depletion stress and an increase in the production of the metabolite, lactic acid. Lack of oxygen also resulted in an increase in the metabolite glycerol-3-phosphate.

The results can give an impression of the effects of stress that can occur in connection with slaughtering of pigs.

"The findings in my studies with cells correspond very nicely to results in another study in our department in which live pigs were stressed," said Dr Straadt.

In this experiment the pigs ran on a treadmill. Various stress parameters were measured immediately after, one hour after and three hours after the exercise. When the pigs were slaughtered, their meat quality was examined and related to the stress measurements. The results indicate that even though the pigs were stressed they quickly got back on track with regard to certain measured meat quality traits.

"Meat from the pigs that were sampled immediately after slaughter had a higher water loss than meat from pigs that had had the chance to rest for either one or three hours," she said.

This means that meat from pigs that have been stressed immediately prior to slaughter has an increased risk of being less juicy. If the pigs have the chance to rest after the drive to the slaughterhouse and before slaughtering, then this risk is reduced. A rest does not, however, fix another of the stress parameters, namely meat toughness.

"Meat from the stressed pigs was tougher than that from non-stressed pigs whether or not they rested after running," explained Dr Straadt about the other study in the department.

The relations shown between stress measured at the cellular level and in live pigs to meat quality can possibly be used as markers to indicate if a pig has been stressed.

Dr Straadt added: "Perhaps it would be possible to see if the pig has been stressed somewhere along the way in the process, either in the piggery, during transportation or at the slaughterhouse. If awareness of the problem could be heightened and there were methods to measure if the pigs had been stressed, then it would be easier to do something about the problem."

The muscle cell project was carried out in collaboration between the Faculty of Agricultural Sciences and the Faculty of Health at Aarhus University and was funded by the Danish Council for Independent Research, Technology and Production. The project with the live pigs on the treadmill was financed by the EU project Q-PorkChains.