Scanning electron microscopy of thin and soft shells induced by feeding calcium-deficient or vitamin D-deficient diets to laying hens

Vitamin D3 Receptors and Metabolic Enzymes in Hen Reproductive Tissues

In recent years, vitamin D3 has been revealed as an important regulator of reproductive processes in humans and livestock; however, its role in the female reproductive system of poultry is poorly known. The aim of this study was to examine vitamin D3 receptor (VDR and PDIA3) and metabolic enzyme (1α-hydroxylase and 24-hydroxylase) mRNA transcript and protein abundances, and protein localization within the hen ovary, oviductal shell gland, pituitary, liver, and kidney. We demonstrated, for the first time, the patterns of the relative mRNA and protein abundances of examined molecules in the ovary, dependent on follicle development and the layer of follicle wall, as well as in other examined organs. Immunohistochemically, PDIA3, 1α-hydroxylase, and 24-hydroxylase are localized in follicular theca and granulosa layers, luminal epithelium and tubular glands of the shell gland, pituitary, liver, and kidney. These results indicate that reproductive tissues have both receptors, VDR, primarily involved in genomic action, and PDIA3, probably participating in the rapid, non-genomic effect of vitamin D3. The finding of 1α-hydroxylase and 24-hydroxylase expression indicates that the reproductive system of chickens has the potential for vitamin D3 synthesis and inactivation, and may suggest that locally produced vitamin D3 can be considered as a significant factor in the orchestration of ovarian and shell gland function in hens. These results provide a new insight into the potential mechanisms of vitamin D3 action and metabolism in the chicken ovary and oviduct.

Research progress on bird eggshell quality defects: a review

The eggshell quality declined with extending of chicken laying cycles. Eggshell quality is a crucial feature that not only affects consumer preference, but also influences producers' economic profitability. The eggshell ultrastructure consists of mammillary, palisade, and vertical crystal layers. Any defect in shell structure results in a reduction in eggshell quality. Speckled, translucent, pimpled, and soft eggshells are common defects that cause significant financial losses for farmers and food security concerns for consumers. Therefore, reducing the faulty eggshells is critical for poultry production. Defective eggshell quality has been attributed to hereditary factors and external environmental stimuli. As such, improvements can be carried out through selective breeding and environmental control of components such as temperature, moisture, and diet formula balance. In this review, the molecular mechanisms of the main eggshell quality defects (speckled, translucent, pimpled, broken, and soft-shell eggs) and the relevant improvement methods are detailed. We hope this review will serve as a useful resource for poultry production management and effectively increasing eggshell quality.

An Overview of the Current Known and Unknown Roles of Vitamin D3 in the Female Reproductive System: Lessons from Farm Animals, Birds, and Fish

Recent studies have clearly shown that vitamin D₃ is a crucial regulator of the female reproductive process in humans and animals. Knowledge of the expression of vitamin D₃ receptors and related molecules in the female reproductive organs such as ovaries, uterus, oviduct, or placenta under physiological and pathological conditions highlights its contribution to the proper function of the reproductive system in females. Furthermore, vitamin D₃ deficiency leads to serious reproductive disturbances and pathologies including ovarian cysts. Although the influence of vitamin D₃ on the reproductive processes of humans and rodents has been extensively described, the association between vitamin D₃ and female reproductive function in farm animals, birds, and fish has rarely been summarized. In this review, we provide an overview of the role of vitamin D₃ in the reproductive system of those animals, with special attention paid to the expression of vitamin D₃ receptors and its metabolic molecules. This updated information could be essential for better understanding animal physiology and overcoming the incidence of infertility, which is crucial for optimizing reproductive outcomes in female livestock.

Pigmentation of White, Brown, and Green Chicken Eggshells Analyzed by Reflectance, Transmittance, and Fluorescence Spectroscopy

We report on the reflectance, transmittance and fluorescence spectra (λ=200-1200 nm) of four types of chicken eggshells (white, brown, light green, dark green) measured in situ without pretreatment and after ablation of 20-100 μm of the outer shell regions. The color pigment protoporphyrin IX (PPIX) is embedded in the protein phase of all four shell types as highly fluorescent monomers, in the white and light green shells additionally as non-fluorescent dimers, and in the brown and dark green shells mainly as non-fluorescent poly-aggregates. The green shell colors are formed from an approximately equimolar mixture of PPIX and biliverdin. The axial distribution of protein and colorpigments were evaluated from the combined reflectances of both the outer and inner shell surfaces, as well as from the transmittances. For the data generation we used the radiative transfer model in the random walk and Kubelka-Munk approaches.

Why did the dinosaurs become extinct? Could cholecalciferol (vitamin D3) deficiency be the answer?

Palaeontological deductions from the fossil remnants of extinct dinosaurs tell us much about their classification into species as well as about their physiological and behavioural characteristics. Geological evidence indicates that dinosaurs became extinct at the boundary between the Cretaceous and Paleogene eras, about 66 million years ago, at a time when there was worldwide environmental change resulting from the impact of a large celestial object with the Earth and/or from vast volcanic eruptions. However, apart from the presumption that climate change and interference with food supply contributed to their extinction, no biological mechanism has been suggested to explain why such a diverse range of terrestrial vertebrates ceased to exist. One of perhaps several contributing mechanisms comes by extrapolating from the physiology of the avian descendants of dinosaurs. This raises the possibility that cholecalciferol (vitamin D₃) deficiency of developing embryos in dinosaur eggs could have caused their death before hatching, thus extinguishing the entire family of dinosaurs through failure to reproduce.

Ultrastructural analysis of the eggshell: contribution of the individual calcified layers and the cuticle to hatchability and egg viability in broiler breeders

1. Scanning electron microscopy was used to assess the relationship between the layers of the eggshell and egg viability. The relative thickness (absolute and %) of the mammillary, palisade, vertical crystal and cuticle layers relative to the total eggshell were measured over a 30-week laying period in 2 broiler breeder lines having different hatchability rates. 2. A significant difference in hatchability of 5.5% between the breeder lines was observed. However, there was no significant difference in either egg viability or fertility between lines. 3. The relative thickness of the individual calcified layers and the cuticle did not differ between lines. Therefore, variations in the thickness of the individual eggshell layers are unlikely to explain the 5.5% difference in hatchability rate between lines. 4. The thickness of the calcified region did not alter as the broiler hen aged. However, the percent contribution of each calcified layer significantly differed over the egg production period. 5. The cuticle was significantly thinner at the beginning and at the end of the laying period compared to 38 weeks of age. 6. No significant correlation was observed between egg viability and the relative thicknesses of the mamillary, palisade or cuticle layers. In contrast, there was a positive relationship between egg viability and the thickness of the vertical crystal layer. 7. The percent contribution of the mammillary and palisade layers was similar in the thinnest and thickest eggshells, suggesting conservation of the proportions of these layers independent of eggshell thickness.

Immunocytochemical localization of vitamin D receptors in the shell gland of immature, laying, and molting hens

It is accepted that vitamin D is involved in the control of egg calcification in hens. The goal of this study was to localize the vitamin D receptors (VDR) in hen shell gland and to determine whether their localization was dependent on reproductive function. Frozen sections of the shell gland of immature, laying, and molting hens were immunostained for VDR, and the VDR in these tissues were also examined by Western blot analysis. Both apical and basal cells of the mucosal epithelium as well as tubular gland cells showed a strong immunoreaction for VDR in the shell gland of laying hens. In the magnum and isthmus, the basal cells of the mucosal epithelium showed a moderately strong immunoreaction for VDR, whereas the immunoreactions in the apical cells of the mucosal epithelium and tubular gland cells were weak. In the shell gland of immature birds, both the mucosal epithelium and tubular gland cells showed a moderately strong VDR immunoreaction. In molting hens, the mucosal epithelial cells and tubular gland cells showed a strong VDR immunoreaction although the mucosal tissue was regressed. Western blot analysis indicated that the mucosal tissue of the shell gland of immature, laying, and molting hens contained two forms of immunoreactive VDR, which were approximately 58 and 60 kDa. Because VDR were richer in the shell gland than in other oviductal segments, these results suggest that in laying hens the shell gland tissues are one of the significant targets for vitamin D. It is likely that the amount of shell gland VDR increases during sexual maturation and immunoreactive VDR remain even during the molting phase.

Calcium deficient diet, acetazolamide and gas exchange characteristics of avian eggshells

The effects of calcium deficient diet and acetazolamide on the gas exchange characteristics of avian eggshells were independently investigated in two groups of unmated hens (Gallus domesticus). In one group, eggs were collected during both a normal diet (3.00% Ca) and a calcium deficient diet (0.34% Ca). In another group, eggs were collected both before and after acetazolamide administration (200 mg/kg) per os. Eggshell water vapor conductance (GH2O) increased 30% during the calcium deficient diet and was accompanied by a 21% decrease in eggshell thickness (L). Eggshell GH2O increased 200% one day after acetazolamide administration and was not only accompanied by a 36% decrease in L, but also by an 89% increase in total functional pore area (Ap). We conclude that a calcium deficient diet increases GH2O by eggshell thinning with little effect on Ap. On the other hand, acetazolamide profoundly increases GH2O, not only by eggshell thinning but also by a remarkable increase in Ap.

Influence of vitamin D3, 1 alpha-hydroxyvitamin D3, and 1,25-dihydroxyvitamin D3 on eggshell quality, tibia strength, and various production parameters in commercial laying hens

Four hundred 53-wk-old Hyline W36 laying hens were randomly allocated to 10 treatments. The effects of feeding two vitamin D3 metabolites, 1 alpha-hydroxyvitamin D3 [1 alpha-(OH) D3] and 1,25-dihydroxyvitamin D3 [1,25-(OH)2 D3], each at five dietary levels (0, .75, 1.50, 3.00, and 4.50 micrograms/kg of feed) were determined on eggshell quality and tibia strength in commercial laying hens (Experiment 1). In Experiment 2, 1,440 Hyline W36 65-wk-old laying hens were used to determine the effects of four levels of vitamin D3 (0, 500, 1,000, and 1,500 ICU vitamin D3/kg) and three levels of dietary 1,25-(OH)2 D3 (0, .5, and 1.0 microgram/kg of feed) on eggshell quality, tibia strength, and egg production. In Experiment 1, neither 1,25-(OH)2 D3 nor 1 alpha-(OH) D3 affected eggshell quality or production criteria. Tibia weight was increased by adding either 1,25-(OH)2 D3 or 1 alpha-(OH) D3. In Experiment 2, 1,25-(OH)2 D3 increased percentage of shell, shell weight, and egg breaking strength when 0 ICU D3/kg was fed but had no effect at higher levels of vitamin D3. Egg production, feed consumption, and egg weight were also increased with supplemental 1,25-(OH)2 D3 when 0 ICU D3/kg was fed. Tibia weight and tibia breaking strength were also increased by adding 1,25-(OH)2 D3 to the diet. The commercial laying hen metabolizes sufficient 1,25-(OH)2 D3 from dietary vitamin D3 to maintain shell quality but not enough to maintain tibia strength.

Optimal dietary level of 1 alpha,25-dihydroxycholecalciferol for eggshell quality in laying hens

The optimal dietary level of 1 alpha,25-dihydroxycholecalciferol [1,25-(OH)2D3] for eggshell quality was established. White Leghorn hens, 59 wk of age, were fed one of eight diets that contained the same basal ingredients, including 3.1% calcium, but different levels (microgram/kg) or forms of calciferol supplements: no calciferol supplement of any form (56 hens); 27.5 (control) or 55.0 micrograms of cholecalciferol (56 hens each); 3, 5, or 7 micrograms of 1,25-(OH)2D3 (28 hens each); 5 micrograms of 24,25-dihydroxycholecalciferol [24,25-(OH)2D3] with 28 hens; 5 micrograms each of 1,25-(OH)2D3 and 24,25-(OH)2D3 (28 hens). All groups were fed the control diet prior to the 21-wk treatment. The group fed 5 micrograms 1,25-(OH)2D3/kg diet ranked first in specific gravity (SG), e.g., 1.081 versus 1.077 for the control group at Week 21 (P less than .05). The group fed 7 micrograms 1,25-(OH)2D3/kg consumed 30% less feed and laid 20% fewer eggs than the control, but shell quality was not affected. The groups receiving no calciferol supplement or receiving only 24,25-(OH)2D3 laid eggs with significantly lower SG than the control after 2 wk of treatment (1.072 or less versus 1.082 at Week 2). The rest of the treatment groups mentioned were comparable to the control in eggshell quality and egg production. Groups fed the combination of 1,25-(OH)2D3 and 24,25-(OH)2D3 per kilogram of feed, or 1,25-(OH)2D3 alone at 5 micrograms/kg, had significantly higher tibial weights relative to the control group. All groups receiving the diets without cholecalciferol supplementation had markedly reduced hatchability. It was concluded that the optimal dietary level of 1,25-(OH)2D3 for improving eggshell quality without affecting egg production was approximately 5 micrograms/kg and the toxic level was 7 micrograms/kg.

Effect of 1 alpha,25-dihydroxycholecalciferol on egg shell quality and egg production

1. The effect of replacing dietary cholecalciferol (D3) by 1 alpha,25-dihydroxycholecalciferol (1,25-(OH)2D3) on egg shell quality and egg production was tested on 32-week-old White Leghorn laying hens over 9 weeks. 2. Hens fed on a diet supplemented with 5 micrograms 1,25-(OH)2D3/kg diet, tended to lay more eggs, and the eggs had significantly higher specific gravity and percentage shell than eggs from control hens fed on a diet supplemented with 27.5 micrograms D3/kg diet. 3. The effect became apparent after about 4 weeks of treatment and persisted until the end of the test. 4. Hens fed on a diet without D3 supplement started to lay very thin or soft shelled eggs within 4 weeks, suggesting that the birds' reserves of D3 or its metabolites were depleted within this period. 5. The results suggest that 1,25-(OH)2D3 can be substituted for D3 in layer diets to improve egg shell quality.