AVERSION TO CO2 GAS IN PIGS USING APPROACH-AVOIDANCE AND CONDITION PLACE AVOIDANCE PARADIGMS

Abstract Text:  

Weaned pig responses to CO₂ was examined using approach-avoidance and condition-place avoidance paradigms. A preference-testing device was designed with two identical chambers separated by a sliding door and an exhaust sink. Twelve crossbred pigs were individually trained for 5 consecutive days to enter the treatment chamber (TC) when the sliding door was opened to obtain a food reward and had 6 minutes to move freely between the chambers before the test concluded. The same methods were used during the testing phase, with CO₂ concentrations in the TC maintained at one of 3 levels: 10%, 20%, and 30%. Tests concluded when loss of posture (LOP) occurred or after 6 minutes. Pigs experienced each of the CO₂ treatments on gas day (G), preceded by ambient conditions on one baseline day (B) and on one wash out day (W) during three rounds. We hypothesized that pigs would display avoidance at higher CO₂ levels, and when aversion occurred conditioned place avoidance would be observed on the wash out day for that round. Behavior was collected using live observations and video recordings. Latency data were analyzed using PROC GLIMMIX in SAS 9.4 and are presented as LSMEANS ± SEM. During testing, 2 pigs failed to enter TC on any of the days and were removed from the analysis. Of the 10 remaining, all pigs entered TC on all B, G and W days. LOP was displayed by 0 pigs, 5 pigs  and 4 pigs at 10%, 20% and 30% CO₂ respectively (20% = 192 ± 23 s; 30% = 78 ± 6 s). Latency to enter TC was greater on G than B and W (B = 3.3 ± 1.38 s, G = 20.8 ± 8.9 s and W = 10.9 ± 4.5 s; P = 0.0009). Similarly, latency  to leave TC was less on G than B and W days (B = 213.4 ± 37.1 s, G = 48.9 ± 9.1 s, W = 273.1 ± 55.5 s; P <0.0001). Latency to re-enter TC was greater on G than B and W days (B = 37 ± 10.5 s, G = 106.5 ± 27.9 s, W = 12.2 ± 3.8 s; P <0.0001). No consistent differences were observed for CO₂ levels suggesting all the concentrations tested were aversive to pigs to some degree. However, aversion was not sufficient to provoke avoidance behavior by naïve pigs or pigs that lost posture during previous exposure. 

Keywords: aversion testing, carbon dioxide, weaned pigs,