Role of magnesium in egg shell formation in the domestic hen.

1. The effects of feeding diets containing various amounts of magnesium on plasma concentration of calcium and magnesium in the domestic hen were investigated. 2. Plasma concentrations of calcium and magnesium decreased during shell formation in all birds. 3. Plasma magnesium content and egg shell thickness were severely reduced in birds given diets containing either 207 or 132 mg Mg++/kg. 4. Using electron microscopy, a precise correlation was observed between the normal distributions of magnesium and organic material across the egg shell of the domestic hen.

Effects of setting eggs small end up on hatchability and posthatching performance of broilers.

1. Hatchability of fertile eggs incubated with their small ends up (SEU) was 16 to 27% lower than for eggs set with their large ends up (LEU). In addition, the SEU position produced more nonviable chicks. 2. There were no differences in post-hatching performance between the two incubation treatments. 3. A survey in a commercial hatchery revealed that the frequencies of eggs set upside down by mistake varied from 0.3% to 3.4%. The setting of eggs upside down was attributed not to difficulties in distinguishing the large and small ends of the eggs but to human error. A decrease in the number of Grade-A chicks of about 0.2% was observed for every 1% of eggs set upside down, suggesting it may be of economic importance to ensure that the eggs are set properly with their large ends up.

Science and the art of incubation.

The artificial incubation of eggs of domesticated species can now be carried out with a high degree of success. However, advances in understanding about the problems faced by the developing embryo during incubation are still being made; and some may help "fine-tune" the incubation process. This paper deals particularly with the use of egg-cooling during incubation as a means of manipulating takeoff times, the use of water-vapor conductance monitoring by weight to predict the optimal humidity conditions for batches of eggs from different strains and species, cuticle-stripping to improve embryonic respiratory gas exchange, and some aspects of egg hygiene. Problems with hatchability usually can be traced to factors such as infertility, faulty breeder nutrition, disease status, or poor egg handling and hygiene, rather than to faulty incubation technique per se. Outlined here are the steps taken to solve an interesting but serious hatchability problem, the cause of which was traced to the presence of kapok seed meal in the breeder diet.

The relationship between eggshell porosity and air space gas tensions measured before and during the parafoetal period and their effects on the hatching process in the domestic fowl.

The partial pressure of gases in the air space were measured before and during the parafoetal period for domestic fowl eggs of the same initial weight but varying in eggshell conductance. Embryos developed and hatched normally from eggs with a wide range of shell conductance and resultant air space gas partial pressures. Air space PO2 levels measured just before pipping ranged from 55 to 65 mm Hg in low and high conductance eggs, respectively, whilst PCO2 levels ranged from 75 to 55 mm Hg. With increasing shell conductance embryos membrane-penetrated and pipped the shell later, but hatch time was unaffected. Membrane penetration and external pipping appeared to occur in response to the partial pressures of gas in the air space but not in response to one particular level of air space PO2 or PCO2. During the parafoetal stage air space PO2 decreased at about 3.8 mm Hg/h and air space PCO2 increased at about 1.8 mm Hg/h and these rates of change were unaffected by eggshell conductance.

Haematology and morphological changes in young broiler chicks with experimentally induced hypoxia.

The haematology, histology and ultrastructure of day-old broiler chicks subject to experimentally induced hypoxia during incubation were examined. Some birds were allowed to reach five weeks old before examination. All the red blood cell parameters, namely, haemoglobin, packed cell volume and red cell counts were raised significantly in hypoxic birds compared with control material and the results closely resembled the haematological profile of young broilers with an ascitic syndrome. By week 5 these parameters had returned to normal. Morphological changes were seen in all the organs examined from day-old hypoxic chicks. The lungs showed much congestion and large numbers of granulocytes were present in hearts, and testes. In the livers, hepatocytes contained enlarged mitochondria together with a reduction in glycogen content. Congested lungs were seen at five weeks old but recovery to normal morphology was observed in all other organs.

Failure to turn eggs during incubation: effects on embryo weight, development of the chorioallantois and absorption of albumen.

Turning eggs during incubation is essential for good hatchability. In the present paper additional effects on the development of the chorioallantois, absorption of albumen and growth of the embryo are recorded. The ability of an unturned egg to hatch was not affected by egg weight, egg shell porosity or water loss during incubation. The ability of the chorioallantois to spread around the inner surface of the inner shell membrane and the degree of absorption of the residual albumen affected the growth of the embryo and its ability to hatch. Unturned eggs hatched later than eggs which were turned throughout incubation.

Occurrence of waxy-textured yolk in the egg of the domestic hen (Gallus domesticus).

An unusual yolk material (waxy yolk) was identified in some hard boiled yolks of one strain of domestic hen. Its structure was consistent with it being formed from normal yolk through disruption of the yolk spheres. These are normally stable during even long periods of storage. Formation occurs mainly after ovulation, during passage of the egg down the oviduct; only rarely could it be found in the larger follicles of the ovarian hierarchy. In the flock of birds examined the incidence of eggs with waxy yolk was 75% of all eggs laid over a 7 d period. Of the 173 birds tested, the eggs of only 17 birds were totally unaffected; all eggs of 82 birds contained this material. The results of a hatchability trial indicated this material had no apparent influence on the embryo or hatchability.

Effect of two gas mixtures on growth of the domestic fowl embryo from days 14 through 17 of incubation.

Eggs weighing 62.5 +/- 0.5 gm when fresh were incubated in air in a forced-draft incubator for 13 days during which time their shell conductance to water vapor (GH2O) was determined. Eggs whose shells represented the entire range of GH2O values present in the population were then incubated for a further 4 days in either air or an experimental gas mixture. Embryo dry weights were determined after a total of 408 hr of incubation to assess the affect of the experimental gas mixture on embryonic development. Embryo growth was found to be stimulated for all eggshell conductances by 4 days incubation in a 50% oxygen/50% nitrogen mixture. This suggests that the decrease in oxygen within the egg that occurs during development normally limits embryonic growth. Growth of the embryo was unaffected by 4 days incubation in a mixture of 17% oxygen/83% helium. This mixture reduced the carbon dioxide tension in the airspace but did not affect the oxygen tension relative to eggs incubated in air. It is suggested, therefore, that the carbon dioxide that builds up within eggs during incubation does not limit embryo growth.

A note on eggshell porosity, nest humidity and the effects of DDE in the grey heron (Ardea cinerea).

Water vapour conductance (GH2O) was determined for 25 grey heron Ardea cinerea eggs in the laboratory, and in nests during natural incubation at two Scottish colonies. The mean GH2O of eggs measured in the nest which successfully hatched was 9.0 mgH2O/mmHg/day and the mean water vapour pressure gradient between egg and nest (delta PH2O), measured using "calibrated" duck eggs, averaged at 31 mmHg (4.13 kPa). Based on eggshell porosity results, from the eggs which hatched, such a gradient would result in a loss of water from the eggs during incubation equivalent to 11% of their fresh weight. Shell thickness, the number of pores/cm2 of eggshell and DDE content were also determined for the 25 eggs measured in the laboratory. Eggs containing high levels of DDE had thinner shells, more pores in the eggshell and a higher overall eggshell porosity. The main problem posed by a high level of DDE would appear, however, not to be an excessive water loss from the egg during incubation, but rather eggshell thinning leading to a loss of the egg due to breakage in the nest.

The effects of eggshell porosity on blood-gas and acid-base status of domestic fowl embryos within eggs of the same weight.

Eggshell porosity affects the metabolism and growth of the developing embryo and is likely, therefore, to influence blood-gas and acid-base status. PO2 in the airspace and in blood from the allantoic vein, PCO2 in the airspace and in blood from the allantoic artery and allantoic vein, and pH of blood from the allantoic artery and vein are all affected by shell porosity. Low porosity eggshells result in an increased retention of carbon dioxide within the egg, in partial compensation for which an increase in the level of bicarbonate in the blood is predicted. It is concluded that some of the wide variation in blood physiology data between eggs at the same stage of incubation, which has been recorded in the scientific literature, is the result of variation in shell porosity between eggs.

Circadian variation in the metabolic rate of growing chickens and laying hens of a broiler strain.

1. Circadian variation in the heat production rate of young broiler chickens and laying broiler hens was studied by indirect calorimetry. 2. Variation in heat production rate was synchronised by the light cycle both in the 23-h light:1-h dark regime of the growing chickens and the 14-h light:10-h dark regime of the laying hens. 3. The relative amplitude of the decrease during the dark phase was about twice as great during the 10 h of darkness afforded the adult hens as it was during the 1-h period of darkness experienced by the growing birds.

The effects of partial defeathering on energy metabolism in the laying fowl.

1. The effects of a complete removal of feathers from the neck and/or breast on the energy metabolism of laying hens were measured by indirect calorimetry. 2. The daily heat production of fed birds was significantly increased if feathers were removed from the entire neck plus breast region but not if the neck only or breast only were denuded. 3. Removal of feathers from neck plus breast led to a 10% increase in food consumption. 4. The partially-defeathered birds laid more eggs.

Effects of food intake regulation on the energy metabolism of hens and cockerels of a layer strain.

1. Indirect calorimetry was used to study the effects on the energy metabolism of cockerels and hens after peak lay of a hybrid layer strain of regulating food or energy intake to 80% of ad libitum for an extended period of time. 2. Regulation of food intake decreased fasting and fed heat productions per bird and per unit metabolic body weight (kg0.75). 3. Maintenance energy requirements (per kg0.75) of both sexes were reduced about 20% by regulation; maintenance requirements of cockerels were about 30% lower per kg0.75 than hens on the same treatments. 4. Reducing the intake of all nutrients by 20% had the same effect on the energy metabolism of cockerels as restricting energy alone by the same amount. 5. Gross efficiency of egg production, in terms of both mass and energy, was higher when intake was regulated. During weeks 21 to 52 of restriction, daily egg mass output was significantly higher in hens fed ad libitum. 6. After 52 weeks of food regulation, restricted hens weighed 20% less and their total carcass energy was 36% less than hens fed ad libitum; similar effects were found in the cockerels.

The effect of rapeseed meal on the energy metabolism of laying hens.

1. The effect of 100 g rapeseed meal (RSM)/kg diet on the energy metabolism of hybrid laying hens was examined by indirect calorimetry. Thyroid hormone concentrations, thyroid weight, liver weight and body weight, egg production and food intake were also measured. 2. Fasting heat production was significantly lower in hens receiving RSM than in controls, but this difference disappeared when the birds were fed. 3. Thyroid hormone concentrations decreased, while thyroid and liver weights increased slightly; none of these effects was significant. Body weight, egg production and food intake were unaffected and no liver haemorrhages were noted. 4. The maintenance metabolisable energy (ME) requirement of control and treated birds, estimated from short-term energy balance measurements, was 474 kJ/kg0.75 d; net availability of ME in both treatments was 0.85.

The fine structure of the pores in the shell of the hen's egg.

No fibrous or crystalline material was present in the lumen of pore canals which were exposed by radial fracture and examined with a scanning electron microscope. The walls of the canals were rough, but they did not have a characteristic ultrastructure. The campanulate outer orifice of the pores was plugged with cuticle in which radial cracks formed channels through which the respiratory gases presumably diffuse.