Prolonged Dark Time Within A 24-h Light Regime Improves Eggshell Quality by Enhancing Calcium Deposition in Laying Hens

Abstract

Background: The absorption and transportation of calcium and phosphorus is mainly relied on their corresponding transporters. Eggshell is mainly formed during dark time in one egg cycle. The aim of this study was to determine the effect of different light regime on eggshell quality and the expression of the relevant calcium and phosphorus transporters in laying hens. Seventy two 56-week-old laying hens were randomly divided into two groups and subjected to the following treatments: 16 h light: 8 h dark (control) and 9 h light: 15 h dark (LDP). The expression of phosphorus transporters type IIb Na/Pi co-transporter NaPi-IIa (NPt2a) and NaPi-IIb (NPt2b), calcium transporter calbindin-D28k (CaBP-D28k), and plasma membrane Ca ATPase 1b (PMCA1b) were measured in small intestine, kidney, and eggshell gland. Results: The results showed that the feed intake (P < 0.001) and egg weight (P = 0.05) was decreased by LDP treatment, while laying rate, egg production, and feed efficiency were not significantly influenced (P > 0.05). Compared to control, eggshell hardness was increased (P < 0.05) by LDP treatment whereas eggshell thickness and eggshell percentage were not significant changed. Eggshell calcium (Ca) and phosphorus (P) contents were elevated in LDP-hens, compared to control birds. Compared to control birds, serum Ca (P < 0.01) and P levels (P = 0.079) at dark time were increased in LDP-hens while and alkaline phosphatase (ALP) activity was lowered (P < 0.05). The protein expression levels of CaBP-D28k and PMCA1b were not influenced in duodenum but were decreased at light time in jejunum of LDP hens. In kidney, the expression of CaBP-D28k, PMCA1b and NPt2a were not changed by LDP treatment. In eggshell gland, however, the expression of CaBP-D28k and osteopontin (OPN) were relative higher in LDP hens compared to control birds, whereas the PMCA1b expression was not altered. Conclusions: The result indicates that the increased circulating Ca and P concentrations in dark time are favorable for the deposition of calcium and phosphorus in eggshell. The result offers an alternative strategy for the laying hen with a worse eggshell problem.