Effects of fine-to-coarse limestone ratio on performance, egg quality, bone traits, and renal CYP27B1 protein abundance in peak and aged Lohmann Brown laying hens.

Two trials were conducted to evaluate performance, egg quality, blood and bone traits, and renal 1α-hydroxylase (CYP27B1) protein abundance in laying hens fed different fine-to-coarse limestone (FL:CL) ratios during distinct production phases. A total of 180 Lohmann Brown hens at 26 weeks of age (Trial 1) and 96 hens at 66 weeks of age (Trial 2) were assigned to dietary FL:CL ratios of 60:40, 50:50, and 30:70 in Trial 1 and 50:50 and 30:70 in Trial 2. In both trials, dietary FL:CL ratios did not affect performance, egg quality, or blood parameters. In Trial 1, the 30:70 FL:CL ratio reduced relative tibia weight and tibia breaking strength (p < 0.05), whereas hens fed the 50:50 ratio exhibited approximately 20 % lower renal CYP27B1 protein abundance (p < 0.05). In Trial 2, the 30:70 ratio increased feed intake (p < 0.05) and reduced tibial Ca content (p < 0.05), while other variables remained unaffected. Overall, altering FL:CL ratios had no effect on eggshell quality and had limited effects on productive performance, but higher proportions of coarse limestone negatively affected specific bone traits. In addition, the intermediate 50:50 FL:CL ratio was associated with lower renal CYP27B1 protein abundance, which is consistent with a reduced demand for vitamin D3 activation and may indicate a more stable Ca homeostasis.