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Assessment of aversion and unconsciousness during exposure to carbon dioxide at high concentration in lambs

By P. Rodriguez, A. Dalmau, X. Manteca, H. Litvan, E. W. Jensen, A. Velarde

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Abstract

The most widely used stunning method in sheep is electrical. However, in lambs, this method leads to rupture of the blood vessels, provoking ecchymoses. In pigs ( Sus scrofa), the use of CO 2-stunning systems has increased in popularity due to positive effects on meat quality and animal welfare (movement of animals in groups). The aim here was to assess the effectiveness of a progressive exposure to 90% carbon dioxide (CO 2) in inducing unconsciousness in lambs ( Ovis aries) through changes in the middle latency auditory-evoked potentials (MLAEP) of the central nervous system (CNS), blood parameters (pH), carbon dioxide partial pressure ( pCO 2), oxygen partial pressure ( pO 2), oxygen saturation (SatO 2) and bicarbonate (HCO 3-), behaviour (head-shaking, sneezing, gasping and gagging) and physiological reflexes (corneal reflex, breathing and sensitivity to pain). Fourteen male lambs of the Ripollesa breed, weighing between 19 and 25 kg, were progressively exposed to an atmosphere of 90% CO 2 over 66 s. All blood parameters changed between 23 and 43 s after the onset of the immersion. The MLAEP did not decrease significantly until after 48 s exposure to CO 2, suggesting an absence of auditory-evoked brain activity. Before that, lambs exhibited head-shaking and sneezing starting at 10.6 (0.77) s, and gasping starting at 20.6 (1.36) s. After exposure, all animals showed absence of breathing and sensibility to pain, and 36% of them absence of corneal reflex. The pH and pCO 2 recovered basal values at 90 and 120 s, respectively, after the end of the exposure. The burst suppression index (BS%) and the A-Line ARX index (AAI) recovered basal levels at 116 and 159 s, respectively. Exposure to CO 2 at high concentration induces effective stunning in sheep for a period of 124 s. However, during exposure, the animals exhibited signs of aversion and breathlessness.

Publication Title Animal Welfare
Volume 25
Issue 1
Pages 73-82
ISBN/ISSN 0962-7286
Language English
Author Address IRTA, Animal Welfare Subprogram, IRTA, Veinat de Sies, s/n 17121, Monells, Spain.antonio.velarde@irta.es
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Tags
  1. Animals
  2. Animal welfare
  3. Blood
  4. Bovidae
  5. Brain
  6. Carbon dioxide
  7. Central nervous system
  8. Effect
  9. Efficacy
  10. Eyes
  11. Lambs
  12. Mammals
  13. Meat.
  14. Pain
  15. peer-reviewed
  16. Pigs
  17. reflexes
  18. Ruminants
  19. ruptures
  20. saturation
  21. Sheep
  22. stunning
  23. Suiformes
  24. systems
  25. Techniques
  26. ungulates
  27. vertebrates
Badges
  1. peer-reviewed