RESUMEN
This study aimed to systematically determined the effect of 28 h ahemeral light cycle on production performance, egg quality, blood parameters, uterine morphological characteristics, and gene expression of hens during the late laying period. At 74 wk, 260 Hy-Line Brown layers were randomly divided into 2 groups of 130 birds each and in duplicates. Both a regular (16L:8D) and an ahemeral light cycle (16L:12D) were provided to the hens. The oviposition pattern in an ahemeral cycle shifted into darkness, with oviposition mostly occurring 3 to 5 h after light out. Production performance was unaffected by light cycle (P > 0.05). Nonetheless, compared to the normal group, the ahemeral group exhibited increased egg weight, eggshell weight, eggshell percentage, yolk percentage, eggshell thickness, and eggshell strength (P < 0.05). There were rhythmic changes in the uterine morphological structure in both cycles, however, the ahemeral group maintained a longer duration and had more uterine folds than the normal group. In the ahemeral cycle, the phases of the CLOCK and PER2 genes were phase-advanced for 3.96 h and 4.54 h compared to the normal cycle. The PHLPP1 gene, which controls clock resetting, exhibited a substantial oscillated rhythm in the ahemeral group (P < 0.05), while the expression of genes presenting biological rhythm, such as CRY2 and FBXL3, was rhythmically oscillated in normal cycle (P < 0.05). The ITPR2 gene, which regulates intracellular Ca2+ transport, displayed a significant oscillated rhythm in ahemeral alone (P < 0.05), while the CA2 gene, which presents biomineralization, rhythmically oscillated in both cycles (P < 0.05). The ahemeral cycle caused 2.5 h phase delays in the CA2 gene compared to the normal cycle. In conclusion, the 28 h ahemeral light cycle preserved the high condition of the uterine folds and changed the uterine rhythms of CLOCK, PER2, ITPR2, and CA2 gene expression to improve ion transport and uterine biomineralization.