Shortened Photoperiod Enhances Protein and Fat Energy Deposition in Growing Pigs

This study examined how different photoperiods affect net energy partitioning and explored the mechanisms via blood biochemistry, gut microbiota, and fecal metabolites. Twelve healthy crossbred pigs (47.7 ± 7.5 kg) were randomly allocated to two groups and subjected to a self-controlled crossover design. Following an 8-day baseline under a normal photoperiod (12L:12D, 12 h light:12 h dark), pigs were assigned to two photoperiod treatment groups: prolonged photoperiod (18L:6D, 18 h light:6 h dark; P group) and shortened photoperiod (6L:18D, 6 h light:18 h dark; S group). Measurements during the baseline (12L:12D) and treatment phases are designated as N1/P (for the P group) and N2/S (for the S group), respectively. The treatment periods were interspersed with the baseline 12L:12D photoperiod and repeated six times. It was observed that, compared to N2, shortened photoperiod (S) had significantly higher net energy deposition, net energy for protein deposition, and net energy for fat deposition (p < 0.05). Compared with N2, plasma low-density lipoprotein in short photoperiod decreased (p < 0.05), and gastric inhibitory peptides increased (p < 0.05). Compared to the prolonged photoperiod, the levels of ghrelin and apolipoprotein A-IV were higher in the shortened photoperiod (p < 0.05). A shortened photoperiod decreased fecal acetic acid compared to N2 (p < 0.05) and decreased propionic acids compared to P (p < 0.05). The significance test of differences between microbial groups showed that there were different microorganisms among the different groups. The results indicated that shortening the photoperiod significantly altered the energy allocation in growing pigs.