Severely depressed pigs exhibit differences in a number of important parameters that may affect gas euthanasia, including decreased respiration rate and tidal volume, according to first-named author, L.J. Sadler of Iowa State University.

In a paper in Animal Welfare with co-authors from Ames, the University of Guelph and AgResearch Ltd in New Zealand, the researchers explain that gas euthanasia of suckling pigs with varied disease severity severely depressed (DP) versus other (OT).

A 2×2 factorial design was utilised with:

• two gas types: carbon dioxide (CO2) or argon (Ar) and
• two flow rates: G = gradual, 35 per cent box volume exchange per minute (BVE per minute) or P = pre-fill + 20 per cent BVE per minute.

Sixty-two pigs were enrolled and tested as DP/OT pairs in each gas treatment combination.

Pigs identified for euthanasia were assigned a subjective depression score (0 = normal to 3 = severely depressed). Pigs scored 3 and ≤1 were categorised as DP and OT, respectively.

Significantly lower respiration, rectal temperature, pulse and weight were observed for the DP pigs than OT.

Pigs were assessed for behavioural indicators of efficacy and welfare.

No differences were observed between DP and OT when using P-CO2 or G-CO2.

In P-Ar, compared to OT, DP had:

• greater latency to loss of consciousness (212±22 versus 77±22 seconds)
• decreased latency to last limb movement (511±72 versus 816±72 seconds)
• greater duration of open-mouth breathing (151±21 versus 69±21 seconds)
• decreased duration ataxia (101±42 versus 188± 42 seconds) and
• decreased righting response (27±11 versus 63±11 seconds).

The G-Ar treatment was removed due to ethical concerns associated with prolonged induction.

Sadler and co-authors concluded that depression score did not affect pig responses to euthanasia with carbon dioxide gas but did affect responses to argon.

Furthermore, they added, argon was associated with a prolonged euthanasia process, including frequencies and durations of distress behaviours.

Reference

Sadler L.J., L.A. Karriker, K.J. Schwartz, A.K. Johnson, T.M. Widowski, C. Wang, M.A. Sutherland and S.T. Millman. 2014. Are severely depressed suckling pigs resistant to gas euthanasia? Animal Welfare 2014, 23: 145-155

August 2014