Driving Pigs to Stunning

Table of Contents

1. Introduction
2. Course content - Driving Pigs to Stunning
   1. Driving system using biological principles
   2. Driving system with no concern for biological principles
   3. Other systems for driving pigs to stunning
   4. Consequences of bad pre-slaughter handling
   5. The slaughter pig
   6. Sensory capacity of the pig
   7. Physical conditions
   8. Social conditions
   9. Handling conditions
   10. Simple ways of making handling easier
   11. Assessment of driving quality
   12. Designing a driving system based on biological principles
   13. Problems that still need to be solved
3. Completion

Problems that still need to be solved

The slaughter industry is characterized by big abattoirs, high slaughter speeds and long transport times. Normally pigs are driven from farm to abattoir several hours before slaughter and about half of all pigs are lairaged overnight. Pigs are mixed in order to keep the variation in liveweight small. In an intact litter of pigs the difference in slaughter weight between the heaviest and the lightest pig is about 30 kg and because of that pigs from the same litter are seldom delivered at the same time.

The chosen stunning method determines the system for driving pigs to stunning. Gas stunning is conducive to humane handling if non-aversive gas mixtures are used. There is still a lack of knowledge about the mechanisms of brain function during application of electrical currents to the head.

Handling pigs in groups is advantageous from an animal welfare point of view. Group handling is based on gas stunning but is not very well suited to electrical stunning. Unfortunately, stunning with high concentrations of CO₂ has recently been found to be aversive to pigs.

Aversion to CO₂. Video: Dr. Raj, University of Bristol.

No aversion to argon. Video: Dr. Raj, University of Bristol.

There is an urgent need for further research on stunning methods and their technical performance. There is also an urgent need for improved and continuing education of staff to ensure good animal welfare.

All forms of transport are potential stressors for animals, and transport also has a negative impact on the environment, so transport time and number of stops should be kept to a minimum. One purpose of lairage is to maintain a reserve, or buffer, of pigs so that the processing line can operate at a constant rate irrespective of variations in the delivery of stock. Under optimal conditions, lairage has the added advantage of giving pigs a chance to rest and drink. Lairage situations can also be very stressful, however, and pig welfare would be improved if they were driven directly from high-quality transport conditions to stunning.

Transport vehicles queuing to unload at an abattoir with bad logistics. Photo: Anne Algers.

High body temperature due to heat and exercise stress during pre-slaughter handling has detrimental effects on animal welfare and meat quality. It is common practice to keep temperatures down by spraying the pigs with cold water during lairage. Unfortunately, this causes problems with water-borne contamination of healthy pigs and handling of large amounts of sewage.

Sprinkler systems decrease temperature during lairage. It also has an effect on the behaviour of the pigs. Photo: Anne Algers.

The repetitive nature of the job of handling large numbers of pigs, and pressures to move the animals to keep up with contracts or slaughter lines, can have the effect of desensitizing handlers to the welfare needs of the animals they are handling. Regular education of handlers, and the use of handling facilities that apply knowledge of the principles of animal behaviour, can make the handling of pigs easier.

The use of electric goads to drive pigs is based on the animals' ability to feel pain. Photo: Anne Algers.