Type of hormonal treatment administered to induce vitellogenesis in European eel influences biochemical composition of eggs and yolk-sac larvae.

Egg biochemical composition is among the main factors affecting offspring quality and survival during the yolk-sac stage, when larvae depend exclusively on yolk nutrients. These nutrients are primarily embedded in the developing oocytes during vitellogenesis. In aquaculture, assisted reproduction procedures may be applied enabling gamete production. For the European eel (Anguilla anguilla), reproductive treatment involves administration of pituitary extracts from carp (CPE) or salmon (SPE) to induce and sustain vitellogenesis. In the present study, we compared the influence of CPE and SPE treatments on offspring quality and composition as well as nutrient utilization during the yolk-sac stage. Thus, dry weight, proximal composition (total lipid, total protein), free amino acids, and fatty acids were assessed in eggs and larvae throughout the yolk-sac stage, where body and oil-droplet area were measured to estimate growth rate, oil-droplet utilization, and oil-droplet utilization efficiency. The results showed that CPE females spawned eggs with higher lipid and free amino acid contents. However, SPE females produced more buoyant eggs with higher fertilization rate as well as larger larvae with more energy reserves (estimated as oil-droplet area). Overall, general patterns of nutrient utilization were detected, such as the amount of total lipid and monounsaturated fatty acids decreasing from the egg stage and throughout the yolk-sac larval stage. On the contrary, essential fatty acids and free amino acids were retained. Notably, towards the end of the yolk-sac stage, the proximal composition and biometry of surviving larvae, from both treatments, were similar.

Porous Yolk-Shell Particle Engineering via Nonsolvent-Assisted Trineedle Coaxial Electrospraying for Burn-Related Wound Healing.

Yolk-shell particles (YSPs) have attracted increasing attention from various research fields because of their low density, large surface area, and excellent loading capacity. However, the fabrication of polymer-based porous YSPs remains a great challenge. In this work, multifunctional polycaprolactone YSPs were produced using trineedle coaxial electrospraying with a simple nonsolvent process. TiO2-Ag nanoparticles and Ganoderma lucidum polysaccharides (GLPs) were encapsulated into the outer shell of the YSPs as the major antibacterial and antioxidant components, whereas iron oxide (Fe3O4) nanoparticles were incorporated into the inner core to act as a photothermal agent. The morphology and structure, chemical composition, biocompatibility, antioxidant, and antibacterial effects of the fabricated YSPs, photothermal effects, and the release profile of the encapsulated GLP were studied in vitro. Furthermore, the in vivo wound healing effects of the YSPs and the laser-assisted therapy were explored based on a burn wound model on c57 mice.

Preparation of Mouse Tissue Lysates for Polymerase Chain Reaction.

A simple cell or tissue lysate can provide a sufficient quality and amount of template DNA for polymerase chain reaction (PCR). This protocol can be used to prepare embryonic tissues or yolk sac samples for PCR analysis, but it is also useful for adult tissues (such as tail) that do not lyse completely by boiling in SDS/NaOH. Nonionic detergents are substituted for SDS because they interfere less with the polymerase reaction.

Isolation of High-Molecular-Weight DNA from Mouse Yolk Sacs and the Like.

Often, genotyping of mouse embryos is required, and a small part, such as the yolk sac, can be used for this purpose. Here, DNA samples are prepared from extra-embryonic tissues by digestion with Proteinase K and subsequent extraction. The yolk sac of mid-gestation or later-stage embryos provides a sufficient amount of DNA for Southern analysis. Small tissues of a few hundred cells are used for genotyping early postimplantation- and preimplantation-stage embryos by polymerase chain reaction (PCR).

Effect of dietary manipulation and vaccination of turkey breeder hens on immunoglobulin levels of yolk, yolk sac and neonate poults.

Two hundred turkey breeder hens and 24 viable toms of 30-35 weeks age of small white variety were distributed into two treatment groups having four replicates of 25 hens and three toms in each treatment. First four replicates were offered a turkey breeder diet (Diet A) (Nutrient requirements of poultry, 1994, National Academic Press, Washington, DC) and the rest four replicates were maintained on a higher plane of nutrition (Diet B) for 8-week duration. After 6 weeks of experimental feeding, two replicates from each treatment groups were vaccinated with ND (R2 B) vaccine. Yolk sac of embryo from birds fed Diet B had a significantly higher (p < .05) IgG, IgM level and HI titre (log 2) than those fed Diet A. HI titre values of embryonic yolk sac from the vaccinated birds fed Diet B were significantly higher (p < .05) than that of the control groups. In addition, HI titre values were significantly higher (p < .05) in the day-old poults of the birds fed Diet B than that of those fed Diet A. There was significantly (p < .01) positive correlation between serum IgG and IgM of the breeder birds and day-old chicks. Similarly, there was significantly (p < .05) positive correlation between yolk IgG and IgM after 1-month experimental feeding and yolk sac IgG and IgM. Positive correlation (p < .05) also existed between yolk sac IgM and day-old chick serum IgM. Furthermore, the HI titres of breeder birds' serum at 14 days post-vaccination were positively correlated with their egg yolk after 10 and 15 days post-vaccination, yolk sac and day-old chicks. Thus, the study envisaged that a higher immunity in neonate poults from turkey breeders maintained on a higher plane of nutrition may be elicited as there was maternal transfer of antibodies from the serum of breeder birds to their offsprings through their yolk sac.

Synthesis of permeable yolk-shell structured gadolinium-doped quantum dots as a potential nanoscale multimodal-visible delivery system.

Developing a nanoscale drug delivery system with magnetic resonance imaging (MRI)/fluorescence imaging (FL) visibility to optimize the delivery efficiency and therapeutic efficacy under image guidance has attracted great attentions in the area of nanomedicine. Herein, a novel permeable yolk-shell structured gadolinium-doped quantum dots nanocomposite was synthesized as a theranostic nanocarrier via an indirectly doping method. The as-prepared permeable nanoparticles with tunable color fluorescent emission, paramagnetic and accessible mesoporous channels could be developed as a novel nanomedical platform for integrated multimodal diagnosis and therapy. The hydrophilic nanocomposites exhibited tunable fluorescence as well as high longitudinal relaxivity (r1 = 17.32mM-1s-1) in water with good colloidal stability. In vivo animal experiments further verified CSSP could achieve FL/MRI dual modality imaging. The widely used antineoplastic anthracycline drug doxorubicin (DOX) was absorbed into the permeable nanospheres with 95.3% loading efficiency and released in a pH-sensitive pattern. In vitro cancer cell cytotoxicity tests verified that the DOX-loaded nanocomposites had enhanced cytotoxicity compared with free DOX at the same concentration. The as-prepared nanocomposites present great potential as MRI/FL-visible nanoscale drug carrier to realize imaging-guided personalized therapy.

Rapid quantification of neutral lipids and triglycerides during zebrafish embryogenesis.

The zebrafish is a useful vertebrate model to study lipid metabolism. Oil Red-O (ORO) staining of zebrafish embryos, though sufficient for visualizing the localization of triglycerides, was previously inadequate to quantify neutral lipid abundance. For metabolic studies, it is crucial to be able to quantify lipids during embryogenesis. Currently no cost effective, rapid and reliable method exists to quantify the deposition of neutral lipids and triglycerides. Thin layer chromatography (TLC), gas chromatography and mass spectrometry can be used to accurately measure lipid levels, but are time consuming and costly in their use. Hence, we developed a rapid and reliable method to quantify neutral lipids and triglycerides. Zebrafish embryos were exposed to Rimonabant (Rimo) or WIN 55,212-2 mesylate (WIN), compounds previously shown to modify lipid content during zebrafish embryogenesis. Following this, ORO stain was extracted out of both the zebrafish body and yolk sac and optical density was measured to give an indication of neutral lipid and triglyceride accumulation. Embryos treated with 0.3 microM WIN resulted in increased lipid accumulation, whereas 3 microM Rimo caused a decrease in lipid accumulation during embryogenesis. TLC was performed on zebrafish bodies to validate the developed method. In addition, BODIPY free fatty acids were injected into zebrafish embryos to confirm quantification of changes in lipid content in the embryo. Previously, ORO was limited to qualitative assessment; now ORO can be used as a quantitative tool to directly determine changes in the levels of neutral lipids and triglycerides.

Zebrafish Embryonic Lipidomic Analysis Reveals that the Yolk Cell Is Metabolically Active in Processing Lipid.

The role of lipids in providing energy and structural cellular components during vertebrate development is poorly understood. To elucidate these roles further, we visualized lipid deposition and examined expression of key lipid-regulating genes during zebrafish embryogenesis. We also conducted a semiquantitative analysis of lipidomic composition using liquid chromatography (LC)-mass spectrometry. Finally, we analyzed processing of boron-dipyrromethene (BODIPY) lipid analogs injected into the yolk using thin layer chromatography. Our data reveal that the most abundant lipids in the embryo are cholesterol, phosphatidylcholine, and triglyceride. Moreover, we demonstrate that lipids are processed within the yolk prior to mobilization to the embryonic body. Our data identify a metabolically active yolk and body resulting in a dynamic lipid composition. This provides a foundation for studying lipid biology during normal or pharmacologically compromised embryogenesis.

Incubation temperature manipulation during fetal development reduces adiposity of broiler hatchlings.

Broilers are known as an efficient source of lean meat. Genetic selection resulted in broiler strains with large body size and fast growth, but a concomitant increase in fat deposition also occurred. Other than reducing nutrient intake, there is a lack of alternative methods to control body fat composition of broilers. The present study assessed whether incubation temperature (machine temperatures: 36ºC, 37.5ºC, and 39ºC; eggshell temperatures: 37.4 ± 0.08°C, 37.8 ± 0.15ºC, and 38.8 ± 0.33°C, respectively.) from d 13 affects broiler hatchling fat deposition. We analyzed adipocyte hypertrophy and proliferation in 3 body regions; weight and chemical composition of yolk-free chicks and yolk sacs; and serum lipid profile. Increased incubation temperature reduced abdominal and cervical adipocyte size. Independently of temperature, cervical adipocytes were smaller and showed higher proliferation than adipocytes in the abdominal and thigh regions. Smaller cervical adipocytes were observed in birds from eggs incubated at 36ºC and 39ºC. With regard to weight and composition of chicks, ash content as a percentage of dry matter was the only variable affected by temperature; it was higher in chicks from eggs incubated at 36ºC than at 39ºC and showed no significant difference between chicks incubated at 39ºC and 37.5ºC. Absolute and relative weights of yolk sacs were higher from eggs incubated at 39ºC than at 36ºC, and these two treatments did not differ from the 37.5ºC control. Absolute measures of yolk sac lipids, moisture, dry matter, and crude protein content were lower in chicks from eggs incubated at 36ºC, and no significant differences were found for these variables between chicks from eggs incubated at 37.5ºC and 39ºC. Hatchlings from eggs incubated at 36°C had significantly higher cholesterol levels than chicks incubated at the other 2 temperatures, but no additional effects on blood lipids were detected. Incubation temperature manipulation during fetal development altered cervical and abdominal adipocyte size in broiler hatchlings and could become a tool in hatcheries to manipulate chick quality, although further studies are needed to evaluate its long-term effects.

Distribution and accumulation of 10 nm silver nanoparticles in maternal tissues and visceral yolk sac of pregnant mice, and a potential effect on embryo growth.

We examined the distribution of silver in pregnant mice and embryos/fetuses following intravenous injections of 10 nm silver nanoparticles (AgNPs) or soluble silver nitrate (AgNO3) at dose levels of 0 (citrate buffer control) or 66 µg Ag/mouse to pregnant mice on gestation days (GDs) 7, 8 and 9. Selected maternal tissues and all embryos/fetuses from control, AgNP- and AgNO3-treated groups on GD10 and control and AgNP-treated groups on GD16 were processed for the measurement of silver concentrations, intracellular AgNP localization, histopathology and gross examination of tissue morphology. Inductively-coupled plasma mass spectrometry revealed silver in all examined tissues following either AgNP or AgNO3 treatment, with highest concentrations of silver in maternal liver, spleen and visceral yolk sac (VYS), and lowest concentrations in embryos/fetuses. For VYS, mean silver concentration following AgNO3 treatment (4.87 ng Ag/mg tissue) was approximately two-fold that following AgNP treatment (2.31 ng Ag/mg tissue); for all other tissues examined, mean silver concentrations following either AgNP or AgNO3 treatment were not significantly different from each other (e.g. 2.57 or 2.84 ng Ag/mg tissue in maternal liver and 1.61 or 2.50 ng Ag/mg tissue in maternal spleen following AgNP or AgNO3 treatment, respectively). Hyperspectral imaging revealed AgNP aggregates in maternal liver, kidney, spleen and VYS from AgNP-treated mice, but not AgNO3-treated mice. Additionally, one or more embryos collected on GD10 from eight of ten AgNP-treated mice appeared small for their age (i.e. Theiler stage 13 [GD8.5] or younger). In the control group (N = 11), this effect was seen in embryos from only one mouse. In conclusion, intravenous injection of 10 nm AgNPs to pregnant mice resulted in notable silver accumulation in maternal liver, spleen and VYS, and may have affected embryonic growth. Silver accumulation in embryos/fetuses was negligible.

Chicken Egg Shell Membrane Associated Proteins and Peptides.

Egg shells are poultry industry byproducts with potential for use in various biological and agricultural applications. We have been interested in the membranes underlying the calcareous shell as a feed supplement, which showed potential to improve immunity and performance of post hatch poultry. Therefore, to determine their protein and peptide profiles, we extracted the egg shell membranes (ESM) from fresh unfertilized eggs with methanol and guanidine hydrochloride (GdHCl) to obtain soluble proteins for analysis by mass spectrometry. The methanol extract was subjected to matrix-assisted laser desorption ionization (MALDI), electrospray ionization (ESI), high-performance reverse phase liquid chromatographic separation (HPLC), and tandem mass spectrometry (MS/MS) to determine its peptide and protein profiles. The GdHCl extract was subjected to ESI-HPLC-MS/MS following trypsin digestion of reduced/alkylated proteins. Nine proteins from the methanol extract and >275 proteins from the GdHCl extract were tentatively identified. The results suggested the presence of several abundant proteins from egg whites, such as ovoalbumin, ovotransferrin, and lysozyme as well as many others associated with antimicrobial, biomechanical, cytoskeletal organizational, cell signaling, and enzyme activities. Collagens, keratin, agrin, and laminin were some of the structural proteins present in the ESM. The methanol-soluble fraction contained several clusterin peptides and defensins, particularly, two isoforms of gallin. The ratios of the two isoforms of gallin differed between the membranes obtained from brown and white eggs. The high abundance of several antimicrobial, immunomodulatory, and other bioactive proteins in the ESM along with its potential to entrap various microbes and antigens may make it a suitable vehicle for oral immunization of post hatch poultry and improve their disease resistance.

The effect of pigeon yolk sac fluid on the growth behavior of calcium carbonate crystals.

Previous experiments have proved that thermodynamically unstable calcium carbonate vaterite can exist for long periods in the yolk sac of a pigeon embryo. The aim of this article was to demonstrate the effect of in vitro mineralization of yolk sac fluid on calcium carbonate by direct precipitation. Experiments were conducted using pigeon yolk sac fluid and using lecithin extracted from pigeon yolk sac fluid as a control to investigate the regulating effects of the organic components in the embryo on the formation of the calcium carbonate precipitate. Multiple characterization methods were employed to study the various morphological patterns, sizes, crystal growth, and crystal phase transformations of the calcium carbonate precipitates as regulated by the yolk sac fluid extracted at different stages of incubation. The experimental results demonstrate that as the incubation proceeds towards the later stages, the composition and environmental features of the yolk sac fluid become more favorable for the formation of relatively unstable calcium carbonate phases with high energies of the vaterite state. The experiments conducted with extracted lecithin as the template for crystal growth yielded similar results. A large amount of organic molecules with polar functional groups carried by the yolk sac fluid have strong effects and can both initially induce the crystallization and regulate the aggregation of calcium carbonate. Furthermore, this regulation process is found to be closely related to the lecithin contained in yolk sac fluid. These observations confirm the changes in yolk sac fluid composition during incubation have significant effects on the production of vaterite, which implicates the calcium transport during embryo growth.

Incubation temperature influences trade-off between structural size and energy reserves in mallard hatchlings.

The reproductive success of precocial birds depends on investments in clutch formation and incubation. Egg quality strongly affects the phenotypic traits correlated with survival of the hatchling, but parental ability to maintain incubation temperature can also influence hatchling outcomes. The effect of incubation temperature on hatchling phenotype has been widely studied in reptiles but not in birds. The aim of this study was to explore the effects of egg mass and incubation temperature on the incubation period, hatchability, and hatchling phenotype of the mallard (Anas platyrhynchos). Mallard eggs were incubated under six constant incubation temperatures (ranging from 35.0° to 39.0°C). Hatchlings were weighed, and their structural size was measured. Some hatchlings were used for an examination of residual yolk sac mass and basic chemical composition of the yolk-free body. All investigated phenotypic traits except for chemical composition were positively correlated with egg mass. Incubation temperature did not affect hatchling body mass, but increased temperatures led to a decreased yolk-free body mass and structural size of hatchlings and to increased yolk sac mass. Our results suggest that there is a trade-off between the yolk-free body size and energetic reserves in the form of the yolk sac and that this trade-off is modulated by incubation temperature.

Maternal offloading of organochlorine contaminants in the yolk-sac placental scalloped hammerhead shark (Sphyrna lewini).

Elasmobranchs are a group of animals that typically occupy upper trophic levels in food webs and have a propensity to accumulate high contaminant concentrations. To date, few studies have investigated maternal offloading processes in sharks, despite the fact that this process represents a substantial source of exposure for young sharks and is a significant pathway for contaminant redistribution within marine ecosystems. Comparable to mammalian systems, scalloped hammerhead sharks (Sphyrna lewini) utilize a yolk-sac placental strategy to nourish young in utero, which may allow females to transfer contaminants to young. Organic contaminants (PCBs and chlorinated pesticides) were measured in livers of both females and males from several age classes that were collected from U.S. Atlantic waters, including two near-term pregnant females and their embryos. Adult female hammerheads (n = 3) were found to have lower levels of PCBs compared to the younger, adult male (mean ± SD, 11.1 ± 1.0 vs. 22.8 µg g(-1) lw), but had substantially higher concentrations of pesticides (4.1 ± 0.9 vs. 1.9 µg g(-1) lw). Embryos from the two litters (n = 36) had similar levels of summed organic contaminant concentrations (4.6 ± 0.9 µg g(-1) lw) and pregnant females were estimated to offload approximately 0.03-2.3% of their hepatic contaminant load to offspring. While the potential health impacts of these transferred contaminants is unknown, this is the first study to demonstrate that scalloped hammerheads are exposed to a substantial amount of contaminants prior to birth and document maternal offloading of organochlorines in a pseudo-placental shark species. Therefore, future research should continue to investigate the potential adverse effects these contaminants have on elasmobranch physiology.

Yolk sac fatty acid composition, yolk absorption, embryo development, and chick quality during incubation in eggs from young and old broiler breeders.

The objective of the present study was to examine the changes in yolk and yolk sac fatty acid composition and also to investigate egg content, yolk absorption, embryo development during incubation, and chick quality at hatch in eggs from 36- and 52-wk-old broiler breeders. The fatty acid profiles of the yolk, the yolk sac of embryos, and the residual yolk sac of chicks were analyzed before incubation, on d 18, and at hatch, respectively. Yolk sac weight, and embryo weight and length were measured on d 18, and chick weight and length were measured at hatch. Egg weight, yolk and albumen weight, yolk percentage, and yolk:albumen ratio increased as breeder age increased, but the albumen percentage decreased. Yolk absorption in absolute value (g) was higher in embryos from the old flock on d 18 and at hatch. Relative yolk absorption was similar between age groups on d 18, whereas it was higher in the young flock at hatch. Breeder age affected the yolk sac weight and was higher in the old flock during incubation. Embryo or chick weight and length, and yolk-free BW were affected by breeder age during incubation. These parameters were higher in the old flock with a difference of 3.7 g, 0.8 cm, and 2.6 g, respectively, on d 18 and 7.4 g, 1.4 cm, and 6.3 g, respectively, at hatch compared with the young flock. The effect of breeder age on fatty acid composition differed significantly by sampling day. Palmitic, stearic, oleic, and linoleic acids were major fatty acids in the fresh yolk, ranging from 13.02 to 29.24%. These were followed by palmitoleic and arachidonic acids ranging from 1.24 to 7.04%, with the remaining fatty acids below 1%. Higher concentrations of myristic, palmitoleic, and oleic acids and lower concentrations of heptadeconoic, stearic, linoleic, and arachidonic acids were found in the residual yolk sac of the young flock than the old flock. The results showed preferentially selective absorption of some fatty acids by the embryo during incubation.

Characterization of calcium carbonate crystals in pigeon yolk sacs with different incubation times.

Calcium carbonate crystals are known to form in the yolk sacs of fertile pigeon eggs at late stages of incubation. The composition and structure of these crystals were investigated, the crystallization environment was inspected, and the physical chemistry constants of the yolk fluid were determined through the incubation period. Polarized light microscopy was used to observe the generation and distribution of calcium carbonate crystals in the yolk sac. In addition, X-ray diffraction was employed to analyze the composition and crystal phase of the yolk sac. A decalcification and deproteination method was established to analyze the ultrastructure and composition of the crystals, as well as the internal relationship between inorganic and organic phases of the crystals. Additionally, scanning electron microscopy, transmission electron microscopy, X-ray energy dispersive spectroscopy, and Fourier transform infrared spectroscopy were used to evaluate the characteristics of the crystals. Our results demonstrated that the calcium carbonate crystals were mainly composed of vaterite and calcite, with vaterite being the major component. Vaterite, a type of biomaterial generated by an organic template control, presented as a concentric hierarchical spherical structure. The organic nature of the biomaterial prevented vaterite from transforming into calcite, which is more thermodynamically stable than vaterite. Additionally, the configuration, size, and aggregation of vaterite were also mediated by the organic template. This bio-vaterite was found during the incubation period and is valuable in calcium transport during embryonic development.

Effect of manipulation of incubation temperature on fatty acid profiles and antioxidant enzyme activities in meat-type chicken embryos.

Eggs (n = 1,800) obtained from Ross broiler breeders at 32 and 48 wk of age were incubated at either a constant temperature of 37.6°C throughout (T1), or the temperature was reduced for 6 h to 36.6°C each day during embryonic age (EA) 10 to 18 (T2). Yolk sac, liver, and brain fatty acid profiles and oxidant and antioxidant status of liver and brain were measured at EA 14, 19, and day of hatch (DOH). Fatty acid profiles of yolk sac, liver, and brain were influenced by age of breeder with significant breeder hen age × incubation temperature interactions. At EA 14, higher levels of 20:4n-6 and 22:6n-3 had been transferred from the yolk sac to T2 embryos from younger than older breeders, whereas for T1 and T2 embryos, yolk sac 20:4n-6 and 22.6n-3 values were similar for older breeders. Accumulation of 20:4n-6 and 22:6n-3 fatty acids in the liver of T1 and T2 embryos from younger breeders was similar; however, T2 embryos from older breeders had higher liver levels of 20:4n-6 and 22:6n-3 than T1 embryos. At EA 19, liver nitric oxide levels were higher for T2 embryos from younger breeders than those from breeders incubated at T1. Brain catalase levels of T2 embryos from younger breeders were higher than those from older breeders at DOH. Thus, changes in fatty acid profiles and catalase and nitric oxide production of brain and liver tissues resulting from 1°C lower incubation temperature from EA 10 to 18 reflect adaptive changes.

The composition of egg yolk absorbed by fasted ostrich (Struthio camelus L.) chicks from 1 to 7 days posthatching and for ostrich (Struthio camelus L.) chicks from 1 to 16 days posthatching on a prestarter broiler diet.

This study was performed to obtain information on yolk utilization in fasted and fed ostrich chicks posthatching. The fasted trial lasted for 7 d, whereas the fed trial continued for 16 d. Fasted ostrich chicks showed a decrease of 31.3 g of BW, with yolk weight decreasing by 28.9 g daily after hatching. Yolk weight comprised 28% of 1-d-old ostrich chick BW and decreased to 12% at 7 d of age. Only 44.4% of the fasted ostrich chick yolk was assimilated over the trial period. Crude protein content of the yolk decreased by 13.2 g daily. Fat content increased by 1.77% daily, whereas total yolk fat weight decreased with 8.91 g daily. Slaughter weight of fed ostrich chicks increased, with yolk weight decreasing by 16.3 g daily. Yolk content for fed ostrich chicks was 26% of BW at 2 d of age. Ostrich chicks absorb 30% of yolk over the first 4 d, 67% after 8 d, and only deplete the yolk after 14 d posthatch. Fasted ostrich chicks absorbed the yolk content at a rate of 28.9 g/d, compared with 22.3 g/d over the first 8 d and 16.3 g/d over the 16 d for fed ostrich chicks. The CP content of the yolk decreased by 6.84 g daily in fed ostrich chicks, whereas fat content of the yolk increased by 1.39% daily, although total yolk fat weight decreased by 6.61 g daily. Yolk weight and total CP decreased faster over the first 7 d in the fasted ostrich chicks compared with the fed ostrich chicks, which indicated that the decrease in yolk weight could be attributed to absorption of protein from the yolk. Fat content decreased faster over the first 8 d from the yolk of the fed ostrich chicks compared with that from the yolk of the fasted ostrich chicks, which could indicate that external feed has a positive influence on the absorption of fat from the yolk content.

Yolk sac carbohydrate levels and gene expression of key gluconeogenic and glycogenic enzymes during chick embryonic development.

Glycogen and glucose concentrations (mg/g of tissue) and amounts (mg) were determined in the yolks of fertile eggs on the day of set and in the yolk sac (YS) and liver of broiler chick embryos between 11 and 21 embryonic days of age (E). On the day of set, the yolk contained 50 mg of glucose (0.31% of yolk) but did not contain glycogen. During incubation, the amount of glucose in the YS increased from 20 mg on E11 to 60 mg on E19. A parallel increase in YS and liver glycogen concentrations (mg/g) during the last week of incubation implied a similar capacity for glycogen synthesis per gram of tissue. However, due to its larger size, the YS capacity for glycogen storage far exceeded that of the liver, which stored less than 12 mg of glycogen up to E19, as compared with more than 200 mg in the YS. Between E19 and 21, liver and YS glycogen amounts decreased by 10 mg and 100 mg, respectively. These results indicated that the YS is a glycogenic and perhaps gluconeogenic organ. We therefore evaluated the gene expression of glycogen synthase and glycogen phosphorylase as well as gluconeogenic enzymes (fructose 1,6-bisphosphatase, phosphoenolpyruvate carboxykinase, and glucose 6-phosphatase) in the YS membrane and liver by real-time reverse-transcription PCR. Although the YS membrane and liver displayed different patterns of mRNA abundance, the high abundance of fructose 1,6-bisphosphatase mRNA in the YS membrane between E11 and 15, and the expression of phosphoenolpyruvate carboxykinase and glucose 6-phosphatase, supported the postulated gluconeogenic abilities of the YS membrane and indicated its role in providing glucose to the embryo. Thus, glucose is probably synthesized in the YS, stored in the form of glycogen, and toward hatch, the YS may have the potential to transfer 10 times more glycogen-derived glucose to the embryo as compared with the liver. As such, the YS may play a major role in the synthesis and storage of glucose and its supply to the chick embryo toward hatch.

Effect of maternal corticosterone on utilisation of residual yolk sac fatty acids by developing broiler embryo.

1. Increased concentrations of maternal corticosterone are deposited into egg yolk under stress conditions. This experiment investigated the effect of maternal corticosterone on yolk and yolk sac fatty acid profiles of eggs and developing broiler embryos. 2. At 42 weeks of age, 200 broiler breeder females were randomly divided into two groups: maternal corticosterone (MC): 2 mg/hen/d of corticosterone dissolved in 1 mL of 99% ethanol and mixed in the individual daily feed for a 14 d period, and control: 1 mL of ethanol added to the individual daily feed. Hens were inseminated, and eggs were collected daily from d 3 of corticosterone feeding to d 14 and incubated. Fatty acid profiles of egg yolk and yolk sac were analysed before incubation and at 12, 14, 18 and 21 d of incubation. 3. Yolk corticosterone concentrations were greater in MC eggs. Before incubation, eggs from MC had lower DHA (22 : 6 n-3) but higher stearic (18 : 0) and dihomo-gamma linolenic (20 : 3 n-6 Cis 8,11,14) acid content compared with the control. 4. Higher concentrations of stearic (18 : 0), elaidic (18 : 1 tr n-9), eicosenoic (20 : 1 n-9), eicosadienoic (20 : 2 n-6), dihomo-gamma linoleic (20 : 3 n-6) and arachidonic (20 : 4 n-6) acids and lower concentrations of myristic (14 : 0), palmitoleic (16 : 1 n-7), linoleic (18 : 2 n-6) and DHA (22 : 6 n-3) were found at different periods of incubation in the residual yolk sac of MC than from controls. 5. The results suggest that the preferentially selective absorption of fatty acids is related to specific tissue requirements.