Effects of Dietary Calcium and Non-Phytate Phosphorus Interaction on Performance, Egg Quality and Lipid Metabolism of Aged Local Laying Hens

This study aimed to investigate the effects of dietary calcium (Ca) and non-phytate phosphorus (NPP) levels alone and in interaction on performance, egg quality, lipid metabolism, antioxidant capacity and follicular development in aged local laying hens. A total of 900 44-week-old Beijing You Chicken (BYC) laying hens with an average body weight of 2.13 ± 0.12 kg were randomly allocated to nine groups (100 hens/group, four replicates of 25 hens). A 3 × 3 factorial design was used with Ca at 3.0%, 3.4%, 3.8% and NPP at 0.31%, 0.36%, 0.41%, respectively. After 1 week of adaptation, the trial lasted from 45 to 58 weeks of age. The results showed that dietary Ca and the NPP level alone did not affect the egg-laying rate of BYCs during 45–58 weeks (p > 0.05), but their interaction affected egg mass (EM, p = 0.049). The group with 3.0% Ca and 0.31% NPP exhibited the highest EM (0.22 kg). At 52 weeks of age, the dietary Ca level affected yolk color (YC): 3.4% Ca and 3.6% Ca increased YC (p < 0.05). Dietary 0.41% NPP decreased YC (p < 0.05). The Ca and NPP interaction affected the albumen height (AH), Haugh unit (HU) and YC (p < 0.05). The group with 3.0% Ca and 0.41% NPP had the highest AH (5.14) and HU (73.46). At 58 weeks of age, 3.4% Ca indicated the lowest YC (p < 0.05). Moreover, 0.36% NPP had the lowest YC and the highest RYW (p < 0.05). Significant Ca × NPP interactions were observed for eggshell thickness (EST), AH, HU, YC, and egg grade (EG) (p < 0.05). The group with 3.0% Ca and 0.41% NPP exhibited the highest AH, HU, YC, and EG. The Ca × NPP interaction affected high-density lipoprotein cholesterol (HDL-C) and low-density lipoprotein cholesterol (LDL-C) content (p < 0.05). Dietary 0.41% NPP increased serum malondialdehyde (MDA) content (p = 0.020). The group with 3.0% Ca and 0.41% NPP had the lowest serum LDL-C (p < 0.05). Dietary Ca, the NPP level alone, and their interaction might not affect the number of large yellow follicles and graded follicles at 58 weeks of age (p > 0.05). The 0.36% NPP and 0.41% NPP increased the number of small yellow follicles (p = 0.021). The group with 3.4% Ca and 0.36% NPP had the highest number of small yellow follicles (25.75 ± 4.34, p = 0.033). In summary, the dietary Ca and NPP interaction, rather than Ca or the NPP level alone, contributed to egg mass, egg quality, lipid metabolism and small yellow follicles in the late laying period. An excessive NPP level (0.41%) may not bring additional benefits to the late laying hens’ performance and could lead to increased peroxidation in the aging local laying hens.