Interactive Effects of Vitamin A and All-Trans Retinoic Acid on Growth Performance, Intestinal Health, and Plasma Metabolomics of Broiler Chickens

This study investigated the interactive effects of dietary vitamin A (VA) and all-trans retinoic acid (ATRA) on growth performance and intestinal health in broilers. A total of 432 one-day-old male Arbor Acres chicks were assigned to a 2 × 3 factorial design with two VA levels (2000 and 6000 IU/kg) and three ATRA levels (0, 0.25, and 0.50 mg/kg). The maize-soybean meal basal diet contained 180 IU/kg VA without extra VA supplementation. Results showed that compared with 0 mg/kg ATRA, 0.50 mg/kg ATRA enhanced average daily gain (ADG) during days 1-21 (<i>p</i> < 0.05). Compared with 2000 IU/kg VA, 6000 IU/kg VA improved body weight on day 35 as well as ADG and feed intake during days 22-35 and reduced feed conversion ratio over the entire trial (<i>p</i> < 0.05). There were VA × ATRA interactions for the ratio of villus height (VH) to crypt depth (CD) in duodenum as well as VH and CD in ileum on day 21 (<i>p</i> < 0.05). The 0.25 mg/kg ATRA decreased duodenal VH/CD and ileal VH in broilers fed 2000 and 6000 IU/kg VA, respectively (<i>p</i> < 0.05). The 0.50 mg/kg ATRA increased ileal VH in broilers fed both 2000 and 6000 IU/kg VA (<i>p</i> < 0.05). When birds were fed 6000 IU/kg VA, 0.50 mg/kg ATRA increased ileal CD compared with 0.25 mg/kg CD (<i>p</i> < 0.05). On day 35, compared with 0 mg/kg ATRA, 0.25 mg/kg ATRA increased ileal VH while 0.50 mg/kg ATRA decreased ileal CD, and both of them increased ileal VH/CD (<i>p</i> < 0.05). The VA × ATRA interactions for mRNA expression of jejunal <i>Mucin5ac</i> on day 21 and jejunal <i>Occludin</i>, <i>Claudin-1</i>, <i>Mucin 2</i>, leucine-rich-repeat-containing G-protein-coupled receptor 5⁺ (<i>Lgr5⁺</i>), zinc and ring finger 3 (<i>Znrf3</i>), and secreted phosphoprotein 1 (<i>SPP1</i>) on day 35 were detected (<i>p</i> < 0.05). Dietary 0.50 mg/kg ATRA up-regulated jejunal <i>Mucin5ac</i> expression in broilers fed 6000 IU/kg VA on day 21 as well as <i>Claudin-1</i>, <i>Znrf3</i>, and <i>SPP1</i> expression broilers fed 2000 IU/kg VA on day 35 (<i>p</i> < 0.05). The 0.25 mg/kg ATRA down-regulated <i>Occludin</i> expression in broilers fed 6000 IU/kg VA on day 35 (<i>p</i> < 0.05). The 0.25 mg/kg ATRA decreased and increased <i>Lgr5⁺</i> expression on day 35 in broilers fed 2000 and 6000 IU/kg VA, respectively (<i>p</i> < 0.05). Both 0.25 and 0.50 mg/kg ATRA down-regulated <i>Mucin-2</i> expression in broilers fed 2000 IU/kg VA on day 35 (<i>p</i> < 0.05). The VA × ATRA interactions were observed for jejunal retinol dehydrogenase 10 (RDH10), cytochrome P450, family 26, subfamily A, polypeptide 1 (<i>CYP26A1</i>), retinoic acid receptor (<i>RAR</i>) α, and <i>RARβ</i> expression on days 21 and 35 (<i>p</i> < 0.05). Both 0.25 and 0.50 mg/kg up-regulated <i>RDH10</i>, <i>CYP26A1</i>, and RARβ expression in broilers fed 6000 IU/kg VA (<i>p</i> < 0.05). The <i>RAR</i>α expression was up-regulated by 0.50 and 0.25 mg/kg ATRA on days 21 and 35, respectively (<i>p</i> < 0.05). Plasma metabolomics identified 269 VA- and 185 ATRA-associated differential metabolites, primarily enriched in lipid metabolism, vitamin digestion and absorption, and bacterial infection pathways. In conclusion, dietary 0.50 mg/kg ATRA and 6000 IU/kg VA enhanced growth performance, intestinal integrity, and VA metabolism, partly through activation of retinoic acid receptors and modulation of plasma lipid metabolism.