乌骨鸡胚胎发育过程中卵内蛋白质脂肪的变化研究

对乌骨鸡胚胎发育过程中卵内各组成成分(蛋清、蛋黄、胚胎)在不同胚龄(即入孵的第0、3、6、9、12、15、18d和出壳)时蛋白质、脂肪含量变化进行测定与分析．结果表明：在不同胚龄时,蛋清中蛋白质含量显著高于蛋黄,蛋黄中脂肪含量始终高于蛋清;而胚胎中的蛋白质、脂肪逐渐增加。另外,胚胎发育过程中胚胎蛋白质的主要来源是蛋黄中的蛋白质,说明蛋黄是禽类胚胎发育过程中营养需要的主要来源。     

Failure to turn eggs during incubation: Development of the area vasculosa and embryonic growth

Effect of turning of the egg during incubation on development of the area vasculosa of the chick embryo was investigated. The size of the area vasculosa was determined by two methods: direct measurement with calipers and measurement of a template cut from the eggshell by use of an automatic surface area recorder. The effects of turning and additionally the effects of lowered temperature (36°C) on both growth of the area vasculosa by day 7 and embryo growth by day 14 of incubation were investigated. The effects of turning during a critical period for turning, from 3 to 7 days of incubation, were also recorded. Generally, failure to turn eggs retarded growth of the area vasculosa. Turning during the critical period stimulated the extent of growth of the area vasculosa by day 7 of incubation and of subsequent embryonic growth by day 14. Incubation at low temperature resulted both in reduced expansion of the area vasculosa and retarded embryonic growth in a pattern similar to that observed for unturned eggs. It is suggested that turning stimulates development of blood vessels in the area vasculosa via localized increases in blood pressure. The effect of a reduced area vasculosa is considered to retard embryonic development through restricted nutrient uptake from the yolk. The prevailing hypothesis that turning prevents deleterious membrane adhesions is questioned in light of these observations. It is suggested that the physiological basis for the need for turning lies in maximizing the growth rate of the area vasculosa to maximize yolk use and embryonic growth rate.     

Accumulation of calcium and phosphorus in pigeon (Columba livia) embryos

Summary Calcium and phosphorus were measured in the yolk and albumen of fertile pigeon (Columba livia) eggs incubated for 0–17 days, and in embryos and hatchlings. Shell provided most of the calcium for skeletal mineralization of the embryos, whereas phosphorus was derived from the yolk and albumen. Mobilization of calcium from the shell to the embryo commenced at approximately day 11 of incubation, accumulating both in the embryo and the yolk sac. There was 1.4 times more calcium in squab yolk sacs than that contained in newly laid egg yolks. The results suggest that whereas general patterns of calcium and phosphorus accumulation during embryogenesis in altricial birds closely resemble those of precocial birds, calcium mobilization from the shell begins later, proceeds at a slower rate and results in a less mineralized hatchling.CIDA/NSERC Visiting Research Associate Permanent address: Department of Animal Science, University of Peradeniya, Peradeniya, Sri Lanka     

ACID-BASE RELATIONSHIPS WITHIN THE AVIAN EGG

1. In the newly laid egg of the domestic fowl the pH values of the albumen and yolk are about 7.6 and 6.0 respectively. 2. When the egg is stored in air there is a loss of carbon dioxide from the albumen and the pH of this fluid rises to a maximum value of about 9.5. A large proportion of the carbon dioxide which remains in the albumen is in the form of carbonate. 3. In the fertile incubated egg the pH of the albumen attains a maximum value within a period of about 2 days; the albumen then becomes less alkaline and it is nearly neutral by the end of the second week. The increasing acidity of the albumen can be attributed to (a) the secretion of hydrogen ions by the blastoderm and (b) the output of carbon dioxide by developing tissues. 4. During the first 2 weeks of incubation the pH of the yolk progressively increases to a maximum value of about 7.5: there is then a tendency for the pH of this fluid to fall and the yolk that is retained within the body of the hatched chick is slightly acidic. 5. The embryo may never come into direct contact with either the albumen or the yolk when the pH of these fluids are high and low respectively. At the beginning of embryonic development the blastoderm is separated from the albumen by the vitelline membrane and from the yolk by a layer of subgerminal fluid with a maximum pH of about 7.8. The vitelline membrane ruptures on day 4 but by this time the embryo is bathed in amniotic fluid with a pH of about 7.5. 6. The pH of amniotic fluid falls from a maximum value of about 7.5 during week I to a minimum value of about 6.5 during week 2. Amniotic fluid is a simple solution of salts until day 12; albumen then begins to flow into the amniotic cavity and the buffering capacity of amniotic fluid increases. 7. The principal end-product of nitrogenous metabolism in the chick embryo is uric acid and about 100 mg of this substance are deposited within the allantoic cavity. The pH of allantoic fluid may exceed 7.5 during week 1 but falls to 6.0 or below after day 13. 8. The tension of carbon dioxide within the egg is determined by the ratio of the rate of carbon dioxide production by the embryo to the permeability of the shell towards carbon dioxide. For the greater part of the period of incubation the permeability of the shell towards carbon dioxide is constant. Thus, as the carbon dioxide output of the embryo increases, the carbon dioxide tension within the egg rises. 9. The pH of the blood can be defined in terms of the ratio of the bicarbonate concentration to the carbon dioxide tension. There is a progressive increase in the carbon dioxide tension of the blood during the period of incubation but the pH is maintained at about 7.4 by an increase in bicarbonate concentration. 10. Part of the increase in bicarbonate is due to the removal of hydrogen ions from carbonic acid by haemoglobin. There is also a large influx of bicarbonate into the blood, but the source of this bicarbonate is not known; the evidence that renal mechanisms are involved is inconclusive and it is probable that the embryo utilizes the enormous potential store of bicarbonate in the egg shell.     

Effects of incubation temperature on growth and development of embryos ofAlligator mississippiensis

Summary Eggs ofAlligator mississippiensis were incubated at 30 °C and 33 °C throughout incubation up to hatching. Every four days several eggs were opened and the albumen, yolk and extra-embryonic fluids removed and weighed. The embryo was removed and fixed prior to being staged, weighted and measured for various morphometric criteria. Development at 33 °C was accelerated compared with 30 °C in terms of yolk and albumen utilization and embryo growth. Significant losses in yolk mass did not occur until stage 22 at 33 °C but occurred at stage 18 at 30 °C. Different patterns in growth were observed in embryos at the two temperatures at similar morphological stages: between stages 18 and 22 embryos at 33 °C were smaller (in mass and length) compared with embryos at 30 °C despite being morphologically similar. The differences in growth and physiology between embryos at 30 °C (females) and 33 °C (males) were dependent on incubation temperature but not sex. Incubation at 33 °C accelerated both growth and development inAlligator; initially morphogenesis was accelerated by the higher temperature but later, growth rate was accelerated.     

Structure, localization and potential role of a novel molluscan trypsin inhibitor in Lymnaea.

Eggs and egg masses of the freshwater gastropod mollusc Lymnaea provide a microenvironment for developing embryos. Secretions of the exocrine albumen gland of Lymnaea are packaged in the eggs of an egg mass before the eggs are laid externally. The perivitelline fluid that directly surrounds individual oocytes is the main source of nutrition for developing embryos. During early stages of development, the perivitelline fluid is initially internalized by pinocytosis and degraded by lysosomes; in later stages, the embryo ingests the fluid. We previously found that the albumen gland produces large amounts of Lymnaea epidermal growth factor. The albumen gland also appears to produce significant amounts of a novel Lymnaea trypsin inhibitor (LTI), a second peptide that was purified and characterized from Lymnaea albumen gland extracts. The primary structure was determined by microsequence analysis, mass spectrometry, and C-terminal sequence analysis, and showed that LTI is a 57-residue glycosylated peptide. Comparison of the LTI sequence with other known serine protease inhibitors indicates that LTI is a member of the bovine pancreatic trypsin inhibitor family. Reverse phase-high performance liquid chromatography, microsequence analysis, mass spectrometry, and immunocytochemistry demonstrated that abundant amounts of intact LTI are packaged in egg masses. The presence of a trypsin inhibitor in the perivitelline fluid compartment of the egg mass may minimize digestion of peptides and proteins in the perivitelline fluid that are important for the development of the embryo, for example, Lymnaea epidermal growth factor.     

Selenium distribution in eggs of avian species

We studied the effect of egg mass of eight different avian species on Se distribution between egg components and the effect of incubation on Se accumulation by chicken eggshell and shell membrane. Eight groups of birds received a diet without Se supplementation. Unfertile eggs were collected after 35 days of feeding; yolk, albumen, shell and shell membrane were assayed separately for Se. All avian species studied showed identical Se concentration in yolk–albumen complex equal to 38.7 μg Se/100 g, reflecting a linear correlation between yolk–albumen mass and Se content. Shells and shell membrane Se accumulation showed quadratic correlation with the appropriate mass thus explaining unusually high Se concentration in ostrich shell and shell membrane, that reached values 1785 and 1904 μg Se/kg respectively. Incubation of fertile eggs decreased eggshell Se content, the effect being more expressed in eggs from hens fed sodium selenite compared to organic Se utilization (Sel-Plex). It was concluded that shell might be an additional Se source for an embryo.     

Permeability of chicken egg vitelline membrane to glucose, carbohydrate gradients between albumen and yolk

1. In the fertile chicken egg the albumen had higher carbohydrate concentration than the yolk with the highest concentration in the vicinity of the vitelline and shell membranes. 2. The mean half-life of glucose in the albumen was 18 hr during the first day of incubation. 3. Vitelline membrane was found to be freely permeable to glucose both from albumen to yolk and from yolk to albumen. 4. The amount of carbohydrate strongly linked to protein (glycoprotein) is similar in yolk and albumen. 5. There is an in vivo as well as in vitro fixation of free glucose by the albumen proteins. 6. Most carbohydrate of the fertile chicken egg was found to be loosely-linked to protein.     

Yolk androgens and embryo sex: maternal effects or confounding factors?

Maternal effects occur when offspring phenotype is affected by environmental factors experienced by the mother and, in egg-laying species, are often mediated via egg resources. There is currently great interest among behavioural ecologists in maternally allocated yolk androgens, especially their relationship with offspring sex and development. Such studies need embryonic tissue for sexing, however, requiring eggs to be incubated (usually for 3 days). Therefore, there are concerns about whether the androgen concentrations assayed reflect those allocated by the mother. In addition, studies showing sex biases in maternal allocation of androgens could be confounded if male and female embryos uptake or metabolise androgens at different rates. We ran a series of experiments using zebra finch (Taeniopygia guttata) eggs to address these potential confounding factors. First we showed, using eggs naturally incubated for up to 5 days, that eggs containing embryos had lower yolk androgen concentrations than eggs that had failed to form embryos. We then tested various hypotheses for this difference using controlled incubation treatments. Our results suggested that (a) embryo development causes the yolk to become progressively more diluted with albumin; and (b) between 3 and 5 days of incubation embryos start uptaking or metabolising androgens. Crucially, we found no decline in yolk androgen concentration at 3 days incubation, and no evidence for sex-specific rates of uptake or metabolism of androgens. This strongly suggests that yolk androgen levels up to 3 days incubation do reflect those allocated by the mother, and that studies of sex biased maternal allocation of yolk androgens are not confounded by sex differences in embryo development.     

The embryo pancreas is a source of increased yolk amylase in the fertilized eggs of domestic fowls.

The amylases were studied in the yolk of fertilized eggs and in the pancreases of the embryos of domestic fowls. The amylase activity in the yolk increased markedly from 13 days of incubation until hatching, but the activity decreased when the embryos were taken out of the eggs. The isoamylases in the yolk and in the pancreas of the embryo were identical electrophoretically. The amylase occurs mainly in the pancreas of the embryo. We think that the increase in amylase activity in the yolk of fertilized eggs during incubation depends upon the accumulation of pancreatic amylase synthesized by the developing embryo in the egg.     

Effect of egg storage duration and egg turning during storage on egg quality and hatching of broiler hatching eggs

In commercial hatcheries, it is common to store eggs before incubation. One practice to improve hatchability consists in egg turning during this storage. This work aims to highlight the effects of turning on the physicochemical aspects of eggs and, consequently, how this turning can influence the hatching of chicks. An experiment was conducted to evaluate the effects of storage duration and egg turning during storage on egg quality, hatchability, and residual analysis. A total of 7 500 hatching eggs were collected from a 55-week-old commercial Cobb500 breeder flock and storage according to the treatments. The experiment was completely randomized in a 3 × 2 factorial design with three storage periods (4, 8, and 12 days) and egg turning (180° turn of eggs once a day) or no turning during storage, totaling six treatments. Regardless of turning, eggs stored for 4 days weighed more than turned eggs stored for 8 and 12 days, which were similar (P < 0.05). Non-turned eggs experienced an increase in relative shell weight with increased storage duration, and non-turned eggs stored for 4 and 8 days differed from non-turned eggs stored for 12 days (P < 0.05). Albumen pH of turned eggs stored for 4 and 8 days was lower than that of non-turned eggs stored for the same durations (P < 0.05). Albumen pH of turned eggs increased as storage duration increased (P < 0.05). Egg turning increased hatching by 2.02% over that of non-turning (P < 0.05). Eggs stored for 12 days, irrespective of turning, had higher late embryonic mortality (P < 0.05) compared to the other treatments. It was concluded that turning eggs during pre-incubation storage was adequate to improve hatchability of fertile eggs. Storing fertile eggs for 12 days is harmful to egg quality and increases embryo mortality even if eggs were turned.     

Interaction between eggshell temperature and carbon dioxide concentration after day 8 of incubation on broiler chicken embryo development

Carbon dioxide (CO₂) is considered to be an important factor during incubation of eggs. Effects attributed to higher CO₂ concentrations during experiment might be due to confounding effects of other environmental conditions, such as incubation temperature. To disentangle effects of eggshell temperature (EST) and CO₂ concentration, an experiment was conducted. A total of 630 Cobb 500 hatching eggs from 37 to 45 wk commercial breeder flocks were collected and incubated according to treatments. The experiment was setup as a complete randomized 2 × 3 factorial design, resulting in 6 treatments. From day 8 of incubation onward, broiler eggs were exposed to one of two EST (37.8 or 38.9 °C) and one of three CO₂ concentrations (0.1, 0.4 or 0.8%). Eggs were incubated in climate-respiration chambers and metabolic heat production was determined continuously. At day 18 of incubation and at 6 h after hatching, embryo and chicken quality were determined by evaluation of organ weights, navel condition, blood metabolites and hepatic glycogen. Hatching time and chicken length at 6 h after hatching showed an interaction between EST and CO₂ concentration (both P = 0.001). Furthermore, no effect of CO₂ concentration was found on embryo development or chicken quality. Metabolic heat production between day 8 and 18 of incubation was not affected by either EST or CO₂. At day 18 of incubation, an EST of 38.9 °C resulted in a higher egg weight loss, longer embryos, higher yolk free body mass (YFBM) and lower heart weight than an EST of 37.8 °C (all P < 0.008). At 6 h after hatching, an EST of 38.9 °C resulted in a higher residual yolk weight and lower YFBM, liver weight and heart weight than an EST of 37.8 °C (all P < 0.003). Lactate, uric acid and hepatic glycogen were not affected by EST at either day 18 of incubation or at hatch. Glucose was not affected by EST at day 18 of incubation, but at hatch, it was higher at an EST of 37.8 °C than at an EST of 38.9 °C (P = 0.02). It can be concluded that effects of CO₂ concentration (at concentrations ≤0.8%) on embryonic development and chicken quality appear to be limited when EST is maintained at a constant level. Moreover, a higher EST from day 8 of incubation onward appears to negatively affect chicken quality at hatch.     

Maternal impact on egg development in Lymnaea stagnalis: a growth factor is produced by the albumen gland in the reproductive tract

Summary

In the freshwater snail Lymnaea stagnalis, perivitellin fluid is the main source of nutrition for developing embryos; it contains predominantly galactogen and proteins. The fluid is produced by the albumen gland, a large exocrine organ in the female reproductive tract. To further define the protein products of this gland and provide more information about the maternal contribution to egg development, albumen glands were extracted and the extracts purified by reversed-phase HPLC. One major HPLC peak fraction exhibited neurotrophic activity when bioassayed on identified Lymnaea neurons in vitro; it has been partially sequenced and has the highest degree of sequence identity with epidermal growth factor (EGF). These results demonstrate that a growth factor with neurotrophic activity is produced by the albumen gland, and is packaged along with the eggs to serve a growth-promoting function in the embryo.     

Adenosine triphosphate levels in steelhead (Oncorhynchus mykiss) eggs: an examination of turnover, localization and role

The dynamics of energy production and utilization in fish eggs before and shortly after fertilization may be critical for embryo survival. Therefore, the current study examined the turnover of adenosine triphosphate (ATP) as well as examined the possible role and localization of ATP in unfertilized steelhead (Oncorhynchus mykiss) eggs and early embryos. The mean ATP level in unfertilized steelhead eggs was 1.92+/-0.10 (mean+/-S.E.M., n=17) nmol ATP per egg. Exposure of the unfertilized egg to 10 degrees C water (water activation) and fertilization resulted in comparable and substantial decreases (approx. 20-50%) in egg ATP levels within 3 min. This suggests that the energy expended at fertilization is used in response to water activation rather than fertilization per se. Unfertilized eggs maintained in ovarian fluid for 9 days at 10 degrees C under air showed a progressive decline of fertility that reached zero after 6 days. In contrast, no significant changes were seen in ATP levels throughout this 9 days period. Thus, fertility does not positively correlate with egg ATP levels in stored eggs. In the unfertilized egg, the ATP stored in the yolk accounted for approximately 1.5% of the total egg ATP. After fertilization, the concentration of ATP in the yolk increased approximately seven-fold, with the yolk and blastoderm each now accounting for approximately 20% of the total remaining ATP. Finally, to estimate the changes in oxidative metabolism following fertilization, the cyanide (KCN)-sensitive decline in total ATP was determined for unfertilized eggs and 1 day embryos. In the presence of KCN, ATP levels declined to approximately 50% within 24 h in both unfertilized eggs as well as embryos; the rates of ATP decline were not different. Therefore, there was not a discernible increase in ATP generation by oxidative phosphorylation at the time of fertilization.     

Periodic cooling of bird eggs reduces embryonic growth efficiency

For many bird embryos, periodic cooling occurs when the incubating adult leaves the nest to forage, but the effects of periodic cooling on embryo growth, yolk use, and metabolism are poorly known. To address this question, we conducted incubation experiments on eggs of zebra finches (Taeniopygia guttata) that were frequently cooled and then rewarmed or were allowed to develop at a constant temperature. After 12 d of incubation, embryo mass and yolk reserves were less in eggs that experienced periodic cooling than in controls incubated constantly at 37.5 degrees Celsius. Embryos that regularly cooled to 20 degrees Celsius had higher mass-specific metabolic rates than embryos incubated constantly at 37.5 degrees Celsius. Periodic cooling delayed development and increased metabolic costs, reducing the efficiency with which egg nutrients were converted into embryo tissue. Avian embryos can tolerate periodic cooling, possibly by adjusting their physiology to variable thermal conditions, but at a cost to growth efficiency as well as rate of development. This reduction in embryo growth efficiency adds a new dimension to the fitness consequences of variation in adult nest attentiveness.     

Serotonin as a growth factor for chick embryo brain

It has been suggested that biogenic amines, in addition to their role as neurotransmitters, may also act as growth factors in the embryo. In the present work the concentrations of serotonin (5-HT), norepinephrine (NE) and dopamine (DA) were first determined in cerebral hemispheres of chick embryo at 10, 12 and 14 days of continuous incubation at 37.5°C (controls). When the incubation on days 7–10 was at 40°C (experimentals), a procedure known to increase brain weight, brain protein content and brain cell number, the concentration of 5-HT in cerebral hemispheres at day 10 (end of neuron proliferation) was significantly increased; this increase persisted at days 12 and 14 but ceased to be significant. No such increases were observed in the concentrations of NE and DA in experimentals at either day 10, 12 or 14. When 5-HT was injected into albumen of eggs at day 7 (37.5°C), cerebral weights, optic lobe weights and cerebral concentrations of 5-HT at day 10 were significantly increased over non-injected controls. Elevated temperature of incubation (40°C) further increased cerebral weight and 5-HT concentration. Cerebral protein contents and the ratios of cerebral protein/ cerebral DNA at day 10 were also significantly increased but cerebral DNA and body weights were unchanged. The optimal doses have been determined. It is concluded that 5-HT may be a growth promoting or regulating factor for embyronal brain.     

Avidin traps biotin diffusing out of chicken egg yolk

1. The unequal distribution of biotin and biotin-binding proteins between the yolk and albumen of freshly laid chicken eggs provides the potential for time-dependent redistribution of biotin that could affect egg quality, biotin availability, and hatchability. 2. Avidin-bound biotin was measured in albumen next to the shell and next to the yolk in eggs stored up to 23 days. 3. Biotin bound to biotin-binding proteins (BBP-I and BBP-II) was measured at the center and periphery of yolk from the same eggs. 4. After 11 days of storage, significant amounts of biotin from the yolk began to accumulate in the albumen adjacent to the yolk. 5. This transfer is attributed to a change in the vitelline membrane that permits diffusion of biotin, not BBP-I or BBP-II, out of the yolk. 6. The dynamics of this phenomenon suggest that in addition to its antimicrobial role, avidin may be involved in the utilization of biotin by the chick embryo.     

Development in vitro of the metacercaria of Bucephaloides gracilescens (Trematoda: Bucephalidae)

The development of Bucephaloides gracilescens metacercariae was studied using a range of cultivation conditions. The most rapid development occurred at 18°C in a medium containing NCTC 135 supplemented with 25% chicken serum, 25% hen egg yolk and 25% hen egg albumen, with a gas phase of air. Under these conditions, shell-protein synthesis was triggered by day 3 in culture; secondary oocytes were apparent in the ovary by day 10; and egg production began by day 14. Survival of worms in media containing chicken serum was twice as long as that achieved with either whiting or angler fish serum. The ingestion of yolk (feeding) appeared to be a necessary prerequisite to development and egg production. The presence of yolk in the culture medium greatly increased the amount of ³H-thymidine incorporated by the reproductive system of freshly excysted metacercariae but had little effect on the uptake and incorporation of tyrosine. The eggs produced in vitro failed to embryonale and were abnormal in appearance, being non-operculate with irregularly thickened shells.     

Embryonic modulation of maternal steroids in European starlings (Sturnus vulgaris)

In birds, maternally derived yolk steroids are a proposed mechanism by which females can adjust individual offspring phenotype to prevailing conditions. However, when interests of mother and offspring differ, parent–offspring conflict will arise and embryonic interests, not those of the mother, should drive offspring response to maternal steroids in eggs. Because of this potential conflict, we investigated the ability of developing bird embryos to process maternally derived yolk steroids. We examined how progesterone, testosterone and oestradiol levels changed in both the yolk/albumen (YA) and the embryo of European starling eggs during the first 10 days of development. Next, we injected tritiated testosterone into eggs at oviposition to characterize potential metabolic pathways during development. Ether extractions separated organic and aqueous metabolites in both the embryo and YA homogenate, after which major steroid metabolites were identified. Results indicate that the concentrations of all three steroids declined during development in the YA homogenate. Exogenous testosterone was primarily metabolized to an aqueous form of etiocholanolone that remained in the YA. These results clearly demonstrate that embryos can modulate their local steroid environment, setting up the potential for parent–offspring conflict. Embryonic regulation must be considered when addressing the evolutionary consequences of maternal steroids in eggs.     

EGG COMPOSITION AND HATCHLING PRECOCITY IN SEABIRDS*

This paper presents analyses of the composition (shell, yolk, albumen) and of the quality (lipid, protein and water contents) of yolk and albumen of eggs of 25 species of seabirds belonging to the Sphenisciformes, Procellariiformes, Pelecaniformes, and Lari of the Charadriiformes. These data are compared with those published for species in the same orders and suborders, and the combined seabird data are compared with published data for non-seabirds. Variation in the proportionate weight of eggshell is not related to hatchling precocity but is probably due to adaptive differences in nest substratum and the agility of the incubating birds. Lipid and protein contents of yolk, and water content of albumen, are uniform in eggs of all examined species. Protein levels of albumen and water content of yolk and of entire egg contents vary greatly between taxa. Contrary to previous claims there is no simple relationship between egg composition and hatchling precocity. Differences in egg composition will probably only be clearly understood when the nutritional needs of the embryo, and of the hatchling in the time before it regularly obtains food, are known.