Gene Expression of Feed Intake-Regulating Peptides in the Gut–Brain Axis of Laying Hens Housed Under Two Different Egg Production Systems

Intensive farming methods have improved productivity, but public concerns have arisen regarding the welfare of production animals, particularly laying hens, and consumers demand higher animal welfare standards in all animal production systems. This study evaluated the impact of conventional cage (CC) versus cage-free (CF) housing systems on the gene expression of some peptide hormones regulating food intake along the gut-brain axis in laying hens at 80 wks. Sixty thousand Hy-Line Brown hens were reared under commercial farm conditions until week 15. At 16 wks, hens were randomly assigned into two housing systems: CC (450 cm²/bird) and CF (1111 cm²/bird). At week 80, hypothalamic, proventricular, duodenal, jejunal, and ileal tissues were sampled from six hens per system for qPCR analysis. Relative mRNA transcript levels of peptide hormones involved in the regulation of food intake (<i>GHRL</i>, <i>Ghsr</i>, <i>NPY</i>, <i>AGRP</i>, <i>POMC</i>, <i>CCK</i>, <i>CART</i>, <i>CRH</i>, <i>MC4R</i>, <i>MC1R</i>, <i>MC5R</i>) were quantified by qPCR using the most stable reference genes. CC hens exhibited upregulation of duodenal anorexigenic genes (<i>POMC</i>, <i>CCK</i>, <i>CART</i>, <i>CRH</i>) and stress-related <i>MC4R</i>, while CF hens showed higher ileal expression of foraging-related <i>AGRP</i>. No differences were observed in orexigenic peptides (<i>GHRL/Ghsr</i>, <i>NPY</i>). These findings suggest that housing systems differentially modulate gut-brain axis signaling. Specifically, CC environments appear to upregulate satiety signals, whereas CF systems seem to enhance the expression of genes linked to foraging behavior.