Hallgeir Sterten defended his thesis on November 20th 2009

Ane Gro Siri Skjelfjord

Pork quality - Influence of pre-slaughter fasting time, gender and feeding regime

The glycogen content and the process in which glycogen is broken down via the anaerobic pathways to lactate, resulting in the acidification of the muscles has a great influence on several pork quality traits. The overall aim of this thesis was to investigate the effects of the ante-mortem factors pre-slaughter fasting and abattoir lairage time, gender and feeding regime on glycogen metabolism and pH development post mortem and its effect on pork quality. Furthermore, this thesis deals with effects of gender and feeding regime on growth performance and carcass characteristics and of pre-slaughter fasting and lairage time on fighting and skin damage. The study was based on one single experiment conducted in a commercial finishing facility and the pigs were slaughtered at a commercial abattoir, which is positive related to the applicability of the results.

This thesis showed that there was a decrease in liver glycogen stores and glycolytic potential (GP) in M. longissimus dorsi (LD) at slaughter by increased pre-slaughter feed withdrawal time. Proglycogen was degraded in favour of macroglycogen post mortem. The findings of glycogen, glucose-6-phosphate (G-6-P) and lactate content development in LD post mortem indicated that there was a delay in the glycogenolysis in pigs that had experienced short fasting time compared to long fasting time. A short fasting time of 4 h led to a slow decline in pH and a lower ultimate pH (PHu) in the LD compared to a fasting time of 26.5 h which resulted in a rapid pH decline early post mortem and a high pHu. The relationship between GP and pHu was significantly negative.

Furthermore, prolonged pre-slaughter fasting reduced drip loss, resulted in a darker colour and tended to improve tenderness of the LD. Castrates showed lower drip loss, higher lightness values and improved tenderness and juiciness compared to gilts. Ad libitum feeding improved tenderness compared to restricted feeding. Negative relationships between pHu and drip loss and lightness of LD were detected as well as positive relationship between pHu and tenderness.

Moreover, it was shown that castrates grew faster and produced fatter carcasses than gilts, while restricted feeding tended to improve feed efficiency and resulted in leaner carcasses than ad libitum feeding. Besides, prolonged pre-slaughter fasting period and abattoir lairage time led to a reduction of the weight of the gastrointestinal tract and a higher extent of skin damage of the carcass. Strong correlation between skin damage score and pHu of the neck muscle M. semispinalis capitis (SC) was detected.

From results presented in this thesis it can be concluded that:

The muscle glycogen pool can be manipulated by fasting the pigs before slaughter which further affects the glycolytic rate and the pH decline post mortem.

A short fasting time of 4 h led to a delayed degradation of glycogen, slow decline in pH and a lower pHu in the LD compared to a fasting time of 26.5 h which resulted in a rapid breakdown of glycogen and pH decline early post mortem and a high pHu.

Proglycogen was degraded in favour of macroglycogen under anaerobic conditions post mortem.

Prolonged pre-slaughter fasting reduced drip loss, resulted in a darker colour and tended to improve tenderness of the LD.

There were negative relationships between pHu and drip loss and lightness of LD as well as positive relationship between pHu and tenderness.

Aiming a higher pHu in LD and thereby improved water-holding capacity, colour and sensory quality, it should be recommended not to feed the pigs in the morning at the day of slaughter.

Prolonged pre-slaughter fasting period and abattoir lairage time led to a reduction of the weight of the gastrointestinal tract and a higher extent of fighting among animals resulting in skin damage of the carcasses.

pHu in the neck muscle SC was indicative for the extent of fighting and skin damages.

Castrates grew faster and produced fatter carcasses than gilts, while restricted feeding tended to improve feed efficiency and resulted in leaner carcasses than ad libitum feeding.

Castrates produced meat with lower drip loss, higher lightness values and improved tenderness and juiciness compared to gilts.

ad libitum feeding improved tenderness of the LD compared to restricted feeding.

Updated: 24.11.09
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