(1) Background: How to reduce respiratory diseases in animals is a matter of great concern, and this study aimed to investigate the effect of maternal administration with all-trans retinoic acid (ATRA) on the lung health of neonatal pigs. (2) Methods: Fifteen sows were randomly allotted to one of five ATRA groups (0, 4, 8, 16, and 32 mg/kg diet), respectively; on average, from days 12 to 95 after insemination, lung samples of neonatal pigs were harvested for HE staining, 16S DNA sequencing, and transcriptomic analysis. (3) Results: Compared to neonatal pigs from the ATRA0 group, neonatal pigs from the ATRA4 group had an increased (p > 0.05) alveolar number and the thinner (p < 0.05) alveolar septum, higher (p < 0.05) abundance of Akkermansia and unidentified_Mitochondria, and a lower (p < 0.05) abundance of Acinetobacter, Cutibacterium, Stenotrophomonas, Enterobacter, Saccharomonospora, and Alistipes in the lungs. Maternal supplementation of ATRA at 4 mg/kg diet had the benefits of reducing pathogen virulence and drug resistance, but it poses the risk of increasing the resistance to β-lactam antibiotics. In addition, it reduced (p < 0.05) the virulence, drug resistance, and stress tolerant capacity of potential pathogens (Proteobacteria, Acinetobacter, Cupriavidus, and Pseudomonas), enriched the highest number of genes in neuroactive ligand–receptor interaction pathway, and decreased gene expression of CCL11 and IL9 in the asthma pathway. (4) Conclusions: Maternal supplementation of ATRA at 4 mg/kg diet can strengthen the lung health of neonatal pigs by improving alveolar development, decreasing the number and virulence of pathogens, and down-regulating the expression of asthma-related genes.

Newborn piglets in intensive pig farms are often prone to pulmonary diseases due to underdeveloped fetal lung neural systems, and ATRA is often regarded as an important morphogen that displays pleiotropic functions during embryonic development. However, information about the effect of maternal administration with ATRA on the peripheral neural system of fetal lungs is still scare. Fifteen pregnant sows were assigned to the ATRA0 (0 mg/kg diet), ATRA4, ATRA8, ATRA16 and ATRA32 treatment groups and offered their own feed from d12 to d95 after artificial insemination; then two neonatal pigs with birth weights similar to the average birth weight were taken out from each litter for the collection of lung samples, and samples were subjected to immunofluorescence staining, RNA-seq and RT-qPCR assays. Results indicated that compared to newborn piglets from the ATRA0 treatment group, newborn piglets from the ATRA4 treatment group had higher percentages of GFAP-positive astrocyte cells (p < 0.05) and GFAP-TUBB3 colocalization (p < 0.05) in the lungs. KEGG (Kyoto Encyclopedia of Genes and Genomes) analysis showed that differential expressed genes are mainly enriched in the pathways of neuroactive ligand–receptor interaction, GABAergic synapses and cell adhesion molecules. Addition of ATRA at 4 mg/kg to the diet of pregnant sows can enhance the healthy development of the pulmonary nervous systems of fetal pigs.