Effect of gender and halothane genotype on cognitive bias and its relationship with fear in pigs

Abstract

Cognitive bias (CB) has been recently proposed as a tool to study emotions by assessing the cognitive function through behaviour observation. It is based on the premise that subjects in a negative affective state perform more negative judgements about ambiguous stimuli than subjects in positive affective state. This study aimed at investigating if halothane genotype (homozygous Hal-free, NN vs. heterozygous Hal carrier, Nn) and gender (gilts, G vs. entire males, EM) affect the CB in pigs. Moreover, the results of the CB test (CBT) were compared with the results of a novel object test (NOT) in order to assess the influence of fear in the decision taken by pigs during the CBT. The results of both tests were contrasted with the concentration of brain neurotransmitters in four different brain areas in order to analyse the involvement of the dopaminergic and serotonergic pathways on the pigs’ affective state and fear. A total of 48 pigs, in terms of 12Hal-free gilts (NNG), 12Hal carrier gilts (NnG), and 12Hal-free entire males (NNEM) and 12Hal carrier entire males (NnEM) were put on the CBT at the age of 20 weeks and on the NOT four days later. After two days, pigs were slaughtered and four brain structures (amygdala, prefrontal cortex, hippocampus and hypothalamus) were dissected for the analysis of brain neurotransmitters. The CBT and NOT results did not show any effect of the genotype and gender or their interaction on pigs’ emotional response (p>0.10). However, the CBT correlated positively with the NOT (r=0.49; p=0.0005), with pigs classified with a negative CB tending to be more fearful in front of the novel object than those with a positive CB (p=0.05). Moreover, the pigs that took longer to get in contact with the novel object in the NOT also had lower (p=0.013) concentration of dopamine in the prefrontal cortex and increased DOPAC/dopamine ratio in the hypothalamus (p=0.003). These results suggest that fear level plays an important role in the decision taken by the pig dealing with ambiguous stimuli.