Low Birth Weight Impairs Acquisition of Spatial Memory Task in Pigs

Abstract

In commercial pig farming, an increasing number of low birth weight (LBW) piglets are born, due to selection for large litter sizes. While LBW piglets have a higher risk of pre-weaning mortality, a considerable number of these piglets survive to slaughter age. In humans, LBW is a risk factor for long-term cognitive impairments. In pigs, studies examining the post-weaning effects of LBW on cognition have reported contradictory results. Therefore, the current study aimed to assess the effects of LBW on cognitive development in pigs using an improved study design, by (1) testing a larger sample size than previous studies, (2) assessing acute and chronic stress responses to account for a potential altered stress response in LBW pigs, and (3) testing both female and male pigs to account for potential confounding effects of sex. Learning and memory of 20 LBW pigs and 20 normal birth weight (NBW) pigs, both groups consisting of 10 females and 10 males, were compared using a spatial holeboard task. In this task, pigs had to learn and remember the locations of hidden food rewards. After a pig had successfully acquired the task, it was presented with two successive reversal phases during which it was presented with a new configuration of reward locations. The holeboard allows for simultaneous assessment of working and reference memory, as well as measures of motivation, exploration, and behavioral flexibility. Mixed model ANOVAs revealed a transiently impaired reference memory performance of LBW pigs, implying they had more difficulty learning their reward configuration in the holeboard. Also, LBW piglets showed increased pre-weaning hair cortisol concentrations compared to their NBW siblings. No other effects of LBW were found. Sex had no direct or interaction effects on any measures of holeboard performance or stress. It is possible that the enriched housing conditions applied during our study had an ameliorating effect on our pigs' cognitive development. Overall, our results suggest LBW has a negative effect on post-weaning cognitive performance in pigs. This could have welfare consequences as cognitive skills are required for pigs to learn how to correctly respond to their environment.

Discrimination learning and judgment bias in low birth weight pigs

“…Perhaps the enriched housing conditions applied during our study also had such an ameliorating effect on the pigs’performance (Sneddon et al 2000; Grimberg-Henrici et al 2016), resulting in only a mild impairment compared to the NBW pigs. Similar mild effects have also been found for other cognitive domains in LBW pigs, such as spatial learning and memory (Gieling et al 2012; Radlowski et al 2014; Roelofs et al 2018; cf. Antonides et al 2015).…”

“…Further indication that group composition may influence emotional state in pigs comes from a finding of impaired behavioral flexibility in male pigs when housed in a single-sex group (Roelofs et al 2017b). When this study was repeated with mixed-sex housing, no difference in behavioral flexibility between females and males was found (Roelofs et al 2018). The composite effects of various elements of pigs’ social environment are likely complex, as is also indicated by our finding of male pigs responding more pessimistically than females.…”

“…This is important, as LBW is currently the best read-out parameter of intra-uterine growth restriction and its associated effects on brain development in pigs (Wu et al 2006; Gieling 2013). Based on previous studies with humans and pigs, we expected to find both a cognitive impairment (O’Keeffe et al 2003; Gieling et al 2012; Radlowski et al 2014; Yu and Garcy 2018; Roelofs et al 2018) and a more negative judgment bias (Lahti et al 2010; Murphy et al 2015) in LBW pigs. LBW pigs were slower to consistently perform the correct behaviors in response to the correct cues.…”

“…The effects of LBW on post-weaning cognitive performance in pigs are not fully understood, as prior studies have produced contradictory results. For example, LBW pigs have been reported to show impaired (Gieling et al 2012; Radlowski et al 2014; Roelofs et al 2018), similar (Gieling et al 2014) or even improved (Antonides et al 2015) spatial learning and memory compared to normal birth weight (NBW) pigs. Studies aimed at the post-weaning emotional functioning of LBW pigs have mostly relied on physiological measures of stress, mainly plasma cortisol concentration (Rutherford et al 2013).…”

Assessment of Welfare in Groups of Horses with Different Management, Environments and Activities by Measuring Cortisol in Horsehair, Using Liquid Chromatography Coupled to Hybrid Orbitrap High-Resolution Mass Spectrometry

“…This could have been an important bias in case sex influences cortisol concentration in horsehair, independent of the degree of stress. Literature on this topic is scarce, but in general, research agrees on the lack of sex differences in hair cortisol, particularly in other species such as cows and piglets [ 31 ], bears [ 32 ], lynx [ 33 ], pigs [ 34 ], and dogs [ 35 ]. Few studies have been carried out on horses; in one case, higher hair concentrations were found in healthy newborn foals compared to healthy adult horses [ 36 ].…”