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Translucent eggshells negatively affect the appearance of eggs and decrease their economic value. Translocation and accumulation of water from the contents to the shells of eggs are frequent occurrences. Causes of translucent eggshell formation have been investigated, but the primary reason is uncertain. In previous studies, scientists have found that the thickness of the eggshell membrane was significantly different between translucent and opaque eggs. However, there are some conflicts among studies. We performed 2 experiments with 3 breeding flocks of chickens to target the reasons for egg translucence. In experiment 1, eggs of 1,024 Brown-Egg Dwarf Layers (DWL) were used. Approximately 1,600 eggs were collected over 2 consecutive days. They were stored for 3 days, and then 120 translucent and 120 opaque eggs were selected for measurement of egg quality traits and weight loss over several weeks. In experiment 2, we used DWL and White Leghorn pure line (WLL) for assessment of eggshell ultrastructure and membrane traits. We chose 120 translucent and 120 opaque eggs from 3,500 DWL eggs and 125 translucent and 125 opaque eggs from 5,028 WLL eggs. The results are as follows: (1) translucent eggs had greater eggshell strength and lower ultimate failure stress of shell membrane than opaque eggs in both DWL and WLL groups, (2) translucent eggs had thicker shells and thinner shell membranes than opaque eggs in DWL, (3) no significant differences were found in either gas pore or bubble pore traits between translucent and opaque eggs in either line, and (4) no significant differences were detected in internal egg quality or weight loss between translucent and opaque eggs in either line. In summary, the present study suggests that variations in both eggshells and shell membrane structures are implicated in the formation of translucent eggs. [ABSTRACT FROM AUTHOR]

The signal pathway of target of rapamycin (TOR) plays an important role in regulating cell growth and proliferation, follicular development, and ovulation. Melatonin (N-acetyl-5-methoxytryptamine) (MT) is involved in the regulation of many physiological functions in animals. Recent studies have shown that MT affects the number and the degree of maturation of follicles in the ovary, but there are few studies concerning its mechanism. Therefore, the aim of this study was to investigate the mechanism of TOR signal pathway in the regulation of ovarian function byMT in aging laying hens. In the present study, a total of 60 hens (70-week-old) were randomly divided into 2 groups: control group and melatonin group (M). Melatonin was administered intraperitoneally at a dose of 20mg/kg/D for 28 D in theMgroup. The results showed that MT significantly increased the levels of the antioxidant enzymes superoxide dismutase and total antioxidant capacity (P < 0.01) as well as levels of immunoglobulin (IgA, IgG, and IgM) (P < 0.05) and the reproductive hormones estradiol and luteinizing hormone (P < 0.01) in the plasma and also increased the numbers of middle white follicles and small white follicles (P < 0.05) and decreased the level of reactive oxygen species in plasma (P< 0.01) in laying hens. There were higher expression levels in MT receptor A (P < 0.05), melatonin receptor B (P < 0.01), and tuberous sclerosis complex 2 (P < 0.01). Activation of TOR, 4E binding protein-l (4E-BP1), and ribosomal protein 6 kinase (P < 0.01) was found in the M. The levels of mTOR and p-mTOR protein were increased in theM(P, 0.05). The mTORC1-dependent 4E-BP1 and p-4E-BP1 were increased in the M (P < 0.05). This study indicated that MT may enhance follicle growth by increasing levels of antioxidant enzymes and reproductive hormones and by activating the mTOR and downstream components in aging laying hens. [ABSTRACT FROM AUTHOR]