Dietary 25-Hydroxycholecalciferol Supplementation as a Vitamin D3 Substitute Improves Performance, Egg Quality, Blood Indexes, Jejunal Morphology, and Tibia Quality in Late-Phase Laying Hens

This study aimed to investigate whether a dietary 25-OHD3 addition improved the performance, egg quality, blood indexes, antioxidant status, jejunal morphology, and tibia quality of aged laying hens compared to a dietary VD3 addition. A total of 270 Hy-Line Brown laying hens at 55 wk of age were randomly assigned to three dietary treatments with six replicates (15 birds per replicate with 3 birds per cage). Chickens were fed a corn–soybean meal diet supplementation of 4000 IU/kg VD3 (control group), 50 μg/kg 25-OHD3 and 2000 IU/kg VD3 (experimental group 1), or 50 μg/kg 25-OHD3 and 4000 IU/kg VD3 (experimental group 2) for 12 weeks. The results demonstrated that 25-OHD3 caused a significant increase in the laying rate, especially in the 50 μg/kg 25-OHD3 + 2000 IU/kg VD3 group; the laying rate reached the maximum compared with other groups after 12 weeks (p < 0.05). However, there were no significant effects on the average egg weight, average daily feed intake, or feed-to-egg ratio (p > 0.05). A dietary supplementation of 50 μg/kg 25-OHD3 and 2000 IU/kg VD3 provided an improved eggshell strength, thick albumen height, and Haugh unit after 12 weeks (p < 0.05). Further analysis of the blood indexes showed that alanine aminotransferase, aspartate aminotransferase, alkaline phosphatase, calcium, and phosphorus were enhanced significantly in the 50 μg/kg 25-OHD3 + 2000 IU/kg VD3 group, while the content of total bilirubin decreased significantly (p < 0.05). In addition, the 25-OHD3 addition in diets improved the calcium and phosphorus contents in the serum (p < 0.05). The concentrations of 25-OHD3, parathyroid hormones, follicle-stimulating hormone, and progesterone were increased in the 50 μg/kg 25-OHD3 + 2000 IU/kg VD3 group, and the levels of cortisol, calcitonin, bone gla protein, and endotoxin in the serum reached a minimum in the 50 μg/kg 25-OHD3 + 4000 IU/kg VD3 group (p < 0.05), which constitutes an advantage for the aged laying hens. The antioxidant enzyme activities and free radical scavenging abilities in the 50 μg/kg 25-OHD3 + 2000 IU/kg VD3 group increased markedly, and the MDA level decreased significantly in the 50 μg/kg 25-OHD3 + 4000 IU/kg VD3 group (p < 0.05). Improvements in jejunal morphology and intestinal integrity resulted in an increased villi-length-to-crypt-depth ratio in the 50 μg/kg 25-OHD3 + 2000 IU/kg VD3 group (p < 0.05). Dietary 50 μg/kg 25-OHD3 and 2000 IU/kg VD3 additions improved the tibia quality, including fresh tibia weight, strength, mineral content (Ca), and trabeculae area (p < 0.05). Taken together, compared with the dietary VD3 addition, dietary supplementation of 25-OHD3 supported a stable physiological status for sustained egg production, egg quality, and bone quality in late-phase laying hens, and the addition levels of 50 μg/kg 25-OHD3 and 2000 IU/kg VD3 had the best effect. Therefore, this could provide a theoretical basis for the use of 25-OHD3 as a substitute forVD3.