Abstract
Low birth weight (LBW) is a risk factor for cognitive and emotional impairments in humans. In pigs, LBW is a common occurrence, but its effects on cognition and emotion have received only limited scientific attention. To assess whether LBW pigs suffer from impaired cognitive and emotional development, we trained and tested 21 LBW and 21 normal birth weight (NBW) pigs in a judgment bias task. Judgment bias is a measure of emotional state which reflects the influence of emotion on an animal’s interpretation of ambiguous stimuli. Pigs were trained to perform a specific behavioral response to two auditory stimuli, predicting either a positive or negative outcome. Once pigs successfully discriminated between these stimuli, they were presented with intermediate, ambiguous stimuli. The pigs’ responses to ambiguous stimuli were scored as optimistic (performance of ‘positive’ response) or pessimistic (performance of ‘negative’ response). Optimistic or pessimistic interpretation of an ambiguous stimulus is indicative of a positive or negative emotional state, respectively. We found LBW pigs to require more discrimination training sessions than NBW pigs to reach criterion performance, suggesting that LBW causes a mild cognitive impairment in pigs. No effects of LBW on judgment bias were found, suggesting a similar emotional state for LBW and NBW pigs. This was supported by comparable salivary and hair cortisol concentrations for both groups. It is possible the enriched housing conditions and social grouping applied during our study influenced these results.
Highlights
Low birth weight (LBW) is a known risk-factor for impaired cognitive and emotional development in humans
For each LBW piglet, a normal birth weight (NBW) piglet was selected from the same litter based on two criteria: (1) piglet had the same sex as the selected LBW piglet, and (2) birth weight was closest to litter average
LBW piglets had on average a lower birth weight than NBW piglets (LBW: 0.83 ± 0.10, NBW: 1.47 ± 0.23; t28.45 = − 11.76, P < 0.001, 95% CI [− 0.75, − 0.53])
Summary
Low birth weight (LBW) is a known risk-factor for impaired cognitive and emotional development in humans. Being small for gestational age increases the risk of developing emotional disorders (e.g., anxiety disorder, depression) in preterm babies (Boyle et al 2011; Lahat et al 2017). Together, these studies show that LBW can have long-lasting effects on the highly associated processes of cognitive and emotional functioning (Lazarus 1982). LBW is becoming a common occurrence in commercially housed pigs. This is a result of sows producing increasingly large litters (Rutherford et al 2013) and being
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