Long-24-h ahemeral light cycle improved eggshell quality of hens in late laying period

Previous study indicated that long-24-h ahemeral light cycle could ameliorate the deterioration of eggshell quality, a significant issue in the later stages of egg production; nevertheless, the underlying process remains unclear. This study explored the mechanism of the long-24-h ahemeral light cycle improving eggshell quality of hens in late laying stage. Two sets of 260 Hy-Line brown laying hens, aged 74 weeks, were randomized, with 65 chickens in each group. One was treated to a standard light cycle (24 h, 16L:8D), whereas the other was subjected to a long-24 h ahemeral light cycle (28 h, 16L:12D). The experimental cycle was 12 weeks. The results indicated that the long-24 h ahemeral light cycle did not influence laying performance (P > 0.05); however, eggshell strength and thickness was dramatically enhanced (P < 0.05). The serum levels of 1,25(OH)₂D₃ and ALP exhibited comparable changes, whereas PTH, PCT, and OT displayed contrasting variations between the two groups. Transcriptome sequencing revealed 889 common genes exhibiting rhythmic expression in both groups, with an average phase advance of 7.41 h. In comparison to the 16L:8D group, 97.41 % of genes exhibited phase advancement in the 16L:12D group. Based on the findings of the functional analysis, we identified four genes associated with bone metabolism and examined their expression patterns: CTNNB1, BMPR2, BMP7, and PDIA3. The expression trend of BMPR2 gene was similar to that of serum 1,25(OH)₂D₃, and the expression trend of BMP7 gene was similar to that of serum OT. The mRNA expression patterns of PDIA3 and BMP7 were inversely related, whereas CTNNB1 and BMPR2 exhibited comparable trends. The mRNA expression of CTNNB1, PDIA3, and BMP7 correlated with eggshell formation. The mRNA expression of BMPR2 significantly elevated during eggshell formation in the 16L:8D group, whereas it remained low during the daylight in comparison to darkness in the 16L:12D group. In summary, the change of light cycle affects the biological rhythm of laying hens, and we found four genes related to bone metabolism, CTNNB1, BMPR2, BMP7 and PDIA3, which specifically responded to the long-24 h ahemeral light cycle and possibly participated in the improvement of eggshell quality.