Early-life stages impact later feeding behavior and physiology in light-born piglets

Low birth weight (LBW) piglets and those exposed to negative experiences early in life are at higher risk of poor development. This study aimed to investigate the potential imprinting effects of early growth rates on metabolism and feeding behavior in LBW piglets. A total of 128 piglets ([Landrace × Yorkshire] × Pietrain) were selected at weaning 23.1 ± 0.37 d old (5.2 ± 0.94 kg body weight [BW]), including 69 castrated males and 59 females. At 51 d of age, 46 LBW piglets (0.98 ± 0.139 kg) were classified using a 2 × 2 factorial design based on growth rate during the suckling and nursery periods. Average daily gains for fast- and slow-nursery piglets were 315 ± 36.6 and 230 ± 39.0 g/d in the fast-suckling group, and 236 ± 26.9 and 159 ± 21.1 g/d in the slow-suckling group. Thereafter, piglets were euthanized at 58 d-old for sampling of physiological biomarkers in blood and urine, and jejunal gene expression. Postweaning piglet to feeder interactions were recorded daily and BW was measured weekly. Slow-growth piglets during the suckling and nursery periods spent less time at the feeder per day during the first week post-weaning (P < 0.05). Additionally, slow-growing suckling piglets showed a tendency to higher urea (P = 0.087) and lower albumin (P = 0.079) levels, and significantly lower Zn and Gamma-Aminobutyric Acid (P < 0.05) concentrations in blood compared to fast-growth piglets. In urine, the suckling slow-growing piglets had significantly higher urea, sulfur, kynurenine and tryptophan creatinine ratios (P < 0.05), with a trend toward a higher kynurenine/tryptophan ratio (KTR; P = 0.084). Slow-growing nursery piglets presented a low level of Zn in blood, a high level of KYN/Creatinine (P < 0.05) and tended to a high KTR (P = 0.074) in urine. Regarding jejunal gene expression, slow-growing suckling piglets showed a significant higher mRNA abundance of the immune response gene CXCL2 (P = 0.043) with a tendency toward increased mRNA levels of S100A9 and IL-8. Furthermore, there was a tendency to higher mRNA abundance of the protein breakdown gene (SH3RF2) and stress response gene (HSD11β1) (P < 0.10). The results suggest that the effects of the suckling and nursery periods were often independent and early-life experiences in LBW piglets, especially the suckling period, have a significant impact on their overall performance, as reflected in the physiological and behavioral differences observed at the end of the nursery period.