Neurological functioning and fear responses in low and normal birth weight piglets

Abstract

Low birth weight (LBW) piglets are an increasingly common occurrence on commercial pig farms, due to selection for sow fecundity. In humans, LBW is a known risk factor for impaired brain development, resulting in impaired neurological functioning and increased vulnerability to stressors. In pigs, the pre-weaning effects of LBW on neurological and emotional functioning are less well known. To assess neurological development, 60 LBW and 60 normal birth weight (NBW) piglets were subjected to a neurological examination at day one after birth. To assess fear responses, another 60 LBW-NBW pairs were compared in a human approach test (HAT) at three weeks of age. In the neurological exam, neonatal LBW piglets were found to be less likely to display a withdrawal reflex in response to a painful stimulus (P = 0.022) and showed impaired coordination during locomotion on a balance beam (P = 0.030). These findings suggest LBW piglets’ increased neonatal mortality, often due to an impaired ability to compete over food or avoid crushing by the sow, could be influenced by a delayed neuromotor development. No effects of birth weight were found on behavioral responses in the HAT, such as latency to approach an unfamiliar human and rate of vocalizations. This suggests LBW and NBW piglets have similar levels of fear in this test. However, we also found indications that the fearfulness displayed by nursing piglets in the HAT is likely due to the temporary removal from the farrowing pen, instead of the presence of an unfamiliar human. Therefore, we can only conclude that LBW does not influence the behavioral response to this combination of stressors (i.e., social isolation from the sow and the piglets’ litter mates, whilst being in a novel environment), as measured by the HAT. Future studies are required to assess whether fear responses to less salient on-farm stressors are affected by birth weight.