Effect of Stocking Density during CO2 Stunning of Pigs on Induction Time and Activity Level Measured Using AI
Department of Food and Production, Danish Technological Institute, Gregersensvej, DK-2630 Taastrup, Denmark
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Author to whom correspondence should be addressed.
Animals 2024, 14(13), 1953; https://doi.org/10.3390/ani14131953
Submission received: 7 June 2024
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Revised: 26 June 2024
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Accepted: 28 June 2024
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Published: 2 July 2024
(This article belongs to the Collection Welfare of Animals in Livestock Production Systems and at Slaughter)
Simple Summary
The most extensively used method in Europe for stunning pigs before slaughter is exposure to carbon dioxide (CO2) in high concentrations (>80%). However, this method is controversial because it can result in variable degrees of aversive reactions during gas exposure. The variation in reaction among pigs is believed to be affected by different stressful conditions before or during the stunning phase. The stocking density in the gondola may be one factor influencing how stunning proceeds. The aim of this study was to investigate the effect of stocking density on the stunning progress of CO2 under commercial conditions. Both pigs’ reaction to the gas (measured activity level using artificial intelligence (AI)) and induction time (time to loss of posture) were reduced by reducing the number of pigs in the gondola. The result indicates that pig welfare during CO2 stunning can be improved by reducing the stocking density. The result also leads to a point of attention to the ongoing initiatives to find alternatives to CO2. When comparing different gas methods, the number of pigs can be a crucial factor in making the right conclusions. Additionally, the results show that vision-based activity measures could be a useful tool to evaluate stunning.
Abstract
During the CO2 stunning of pigs, a variation in their reaction to the gas and the duration of the induction period is observed. The stunning process can be affected by several conditions, such as stressful events and previous experiences, but the stocking density in the gondola may also have an impact. The objective was to investigate the effect of stocking density on the stunning process under commercial conditions. To quantify the pigs’ reactions under industrial settings with a stocking density of up to eight pigs pr. Gondola (3.91 m2), the activity level was measured using an AI solution. Compared with a simulation of the expected induction period, a significantly longer induction period was found in gondolas containing seven and eight pigs (p < 0.001) but not when the gondolas contained three or four pigs. Both high and mean activity levels were significantly higher when stocking density was increased from three or four pigs to seven or eight pigs. The stunning process was thus negatively affected when increasing the stocking density. More knowledge is needed to explain this effect and to make statements on optimal stocking density. The measured activity levels may be a useful tool for obtaining information under commercial conditions and for documenting animal welfare.
Keywords:
pig; stunning; CO2; loss of posture; animal welfare; artificial intelligence
