Counselling towards better quality pork

Janne Karin Brodin

Up until now no clear, unambiguous advice has been available on the feeding and handling of pigs prior to slaughter for maximum product quality of the pork. In his PhD work, Hallgeir Sterten has investigated conditions connected to slaughter time that affect the sensory quality of the meat.

The feeding and handling of pigs prior to slaughter vary from abattoir to abattoir. The time the animals are at theslaughterhouse before they are slaughtered will also vary, according to the number of animals to be slaughtered and the capacity at the abattoir. The number of hours the animals may remain unfed is regulated in the Norwegian law on animal welfare. For pigs, this is 18 hours. But what is best with regards to meat quality, animal welfare and economics?

Hallgeir Sterten Photo: Janne Brodin

Can pork be improved?
An increase in pH in pork will, up to a point, give better product quality in terms of tenderness, juiciness and colour. An increased pH gives reduced drip loss from the carcass because the fluids stay in the meat after slaughter. This means the carcass weight loses less weight and that the consumer gets meat that is more tender and juicy.

How to affect pH
The finding that meat pH influences meat quality confirms that the link between pH and meat quality parameters is valid also for Norwegian pigs. pH may be influenced via breeding, but feeding regimes can also influence those energy reserves present in the meat which form the basis for the pH development. If there is a high glycogen content – i.e. easily accessible energy – in the meat at slaughter, this will support the anaerobe decomposition of glycogen to lactate which aids pH reduction.

What influences meat quality?
In his doctoral work, Sterten has looked into the effects of varying fasting periods prior to slaughter, the possibility of gender variations, and differences in feeding regimes – ad lib feeding as opposed to restricted feeding.

Pre-slaughter feeding
The results showed that feeding shortly before slaughter influenced meat quality negatively because pH, which is measured about 24 hours after slaughter, becomes too low. It was also found that a long fasting period (26.5 hours) and a long lairage time – waiting time - (23 hours) at the abattoir prior to slaughter influenced meat quality positively, because this gave reduced glycogen stores with resultant increased final pH. A moderate fasting period (17.5 hours) also gave better meat quality compared to a short fasting time of only 4 hours.

Aggression, fighting, stress and animal welfare
Avoiding aggression and fighting among the animals is desired from an animal welfare viewpoint, and damage from fighting and bites decreases meat quality. Damage to skin and to muscle tissue makes the meat unfit for use as bacon, pork ribs or ham. Hunger will increase stress levels and the frequency of fighting between the animals. As well, there is a clear connection between final pH and the degree of fighting damage of carcasses. The conclusion is that if the animals arrive at the abattoir late in the day and must be left overnight, they must be fed.

Gender differences
Gender differences were proven. Tenderness and juiciness were higher in meat from castrates than in meat from gilts. Gender differences are not necessarily related to variations in pH. It is likely that differences in intramuscular fat give rise to the differences in the above meat quality parameters. Lower drip loss and lighter meat colour in castrates than in gilts may also partly be explained by the fact that castrates have a higher intramuscular fat content than gilts.

Ad lib feeding versus restricted feeding
Ad lib feeding resulted in a more tender meat than did restricted feeding. It also led to castrates becoming fatter and having a lower meat percentage than gilts. This may be explained by the fact that castrates are more active and have a larger feed intake than gilts. Gender differences are more pronounced with ad lib feeding than with restricted feeding. Restricted feeding tended to improve feed efficiency and give higher meat percentage than ad lib feeding.

The slaughter process
Stomachs and intestines which are full of feed due to feeding shortly before slaughter is a problem at the abattoirs, because of the increased risk of perforating the stomach or intestine when the carcass is opened. This may lead to contamination and a risk of poor hygienic quality of the meat. Also, feed given shortly prior to slaughter is in many ways wasted, seeing that the animal cannot utilize it properly.

At the slaughterhouse Photo: Bjart Schieldrop

New counselling
The results from this doctoral work will support revised and new guidelines for counselling related to feed and feeding regimes prior to slaughter. Interest in the results has been expressed, first of all on the part of abattoirs, and they will form the basis for new counselling on the handling of animals and on routines for transport and pre-slaughter feeding, both at the producer and during the time the animals stay at abattoirs.

Hallgeir Sterten took his Master degree at IHA/UMB in 1983 in the field of nutrition monogastric animals. He is employed at Felleskjøpet Fôrutvikling in Trondheim as head of development pig feed, where he has been since 1993

The trial lecture and the public defence took place November 20 2009 at IHA.

Disputasen fant sted ved Institutt for husdyr- og akvakulturvitenskap fredag 20. november 2009. Title of the thesis: Pork quality – Influence of pre-slaughter fasting time, gender and feeding regime.

Prescribed subject of the trial lecture: Compensatory growth in pigs – strategies and effect on production and pork quality.

Sterten’s main supervisor has been Associated Professor Nils Petter Kjos. Professor Margareth Øverland, Professor Magny S. Thomassen and Professor Odd Vangen, all IHA have been assistant supervisors.

Published: 07.12.09
Updated: 08.12.09
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