Behaviour of egg shell under compression in relation to deformation measurements1

1. The egg does not completely obey Hook's law when compressed between flat surfaces.

2. Deformation was not completely reversible due to crumbling at the points of contact with the force.

3. There are three components of non‐destructive deformation: (a) local deformation at the points of contact, (b) local surface crumbling and (c) deformation of the over‐all shell structure.

4. The latter two are uncontrolled, contributing to errors in the prediction of fracture force and depending on the non‐destructive force applied.

5. These effects should be considered in test selection and interpretation.

6. The optimum non‐destructive force was found to be 1 kg.     

The artificial production of translucent streaks on egg shells and various factors influencing their development

It is well known that translucent streaks can develop on egg shells due to damage to the surface of the shell. These “artifacts” have been produced under standard conditions and a study of them shows that the rate of development of the translucent areas up to their maximum brightness as measured by a scoring system can be expressed in simple mathematical terms. Having established this it was then possible to show that the rate of development of these translucent areas was (a) inversely related to the time of marking after the egg was laid, (b) directly proportional to external temperature and (c) affected by relative humidity so that a humidity between 10 and 30 per cent gave the maximum rate of development.

Replacing the egg content with water or alcohol gave some interesting results.

It was also found that the translucent streaks were weaker than corresponding opaque areas of the shell. The width of the streak produced under standard conditions varied greatly between the different eggs.

The reasons for these various findings are discussed.     

A study of the fundamental cause of natural translucent areas in egg shells

On candling, eggs often show translucent areas sometimes known as mottling. This is caused by local accummulations of moisture in the shell. A study of natural or “normal” translucence, as distinct from “accidental” translucence, has been made. It was observed that freshly laid eggs have wholly translucent shells which, on drying, develop opacity, often leaving some areas translucent. An early association between natural translucence and an increased shell matrix protein content has been confirmed, and a study of the distribution of this matrix in radial sections of shell has revealed a difference between opaque and translucent shell.

Further there was a difference in the porosity of opaque and translucent shells. These findings could be explained by the presence in opaque shells of a layer of shell low in organic matter, which appears to hinder the passage of moisture through the shell.     

Whitening of brown shelled eggs: Individual variation and relationships with age,fearfulness, oviposition interval and stress

1. Fearfulness, shell colour, incidence and degree of shell whitening and the interval between ovipositions were studied in two populations of 30 brown egg laying hens with family histories of a low or a high incidence of egg shell whitening.

2. Hens of the population with the high incidence of whitening appeared to be more fearful than hens of the population with the low incidence of whitening.

3. Brown colouration of the egg shell and the incidence and degree of shell whitening declined as the hens aged.

4. Brown colouration and egg shell whitening were most pronounced on the blunt ends of the eggs.

5. A large part of the variation in egg shell whitening was attributable to the individual (hen) component of variance.

6. Differences in egg shell whitening, between the two populations, were detectable throughout the 26 weeks of the experiment.

7. Oviposition intervals were similar for normal and coated eggs when birds were not exposed to disturbance.

8. Disturbance of hens increased oviposition intervals and the incidence and degree of shell whitening, to a similar extent, in both populations.

9. It is concluded that stress‐related egg retention is not the sole factor responsible for abnormal egg shell whitening. Shell whitening may occur as a consequence of the premature termination of shell pigmentation as well as a consequence of the retardation of oviposition which occurs when hens are disturbed.     

Relationship between the shell membrane‐shell bond and shell deformation in hens’ eggs

1. The influence of the shell membranes on shell strength was studied in 21 Single Comb White Leghorn eggs.

2. Shell deformation and shell thickness were plotted for each egg and the regression line was calculated. The difference between the observed shell deformation and that predicted by the regression line was calculated for each egg and this distance, with changed sign, was called the shell deformation index.

3. The force needed to separate the shell membranes from a 10 mm wide strip of the shell was determined by a tensile testing machine and was termed attachment strength.

4. The correlation between shell deformation index and attachment strength was highly significant (r=0.88, P<0.0005). Thus the shell membranes contribute to shell strength, probably by serving as a reinforcement of the crystalline part of the shell.     

Factors affecting the non‐destructive and destructive methods of measuring egg shell strength by the quasi‐static compression test1

1. Precise measurements of shell deformation and fracture force were made to examine the destructive and non‐destructive quasi‐static compression tests of egg shell strength.

2. Prediction of shell strength from shell deformation (d) was not greatly improved by combining egg length, diameter and shell thickness with shell deformation. At the equator 54% of the variation in fracture force (F) was accounted for by an equation F = 8467 ‐ 115630i+584166d² compared with 57% when 13 measured and generated parameters were included (singly and in combination) in the analysis.

3. Cracks changed the deformation by an average of 8% providing the crack was not near the points where force was applied. Cracked eggs could be tested to reduce the bias introduced by eliminating such eggs from experiments. Empirical factors must, however, be established to correct such deformation readings.

4. Use of a hole or rubber on the lower compression surface to stabilise the egg increased the force required to fracture the shell at the upper flat surface Such surfaces are undesirable because the fracture site is biased towards the upper contact point when force is distributed at the lower surface. Shell deformation and its correlation with strength was also reduced.

5. The fracture force predicted by a non‐destructive deformation measurement was greatly affected by the force applied. The optimum test force was 1 kg at the equator.     

Effects of short intermittent lighting on food consumption and performance of dwarf broiler breeders and progeny

1. Two hundred and sixty four dwarf broiler breeder hens were subjected to ad libitum or restricted feeding and to four lighting patterns: 15L (bright light):9D (dark), 15L:9d (dim light), 2L:10d: 1L:11d, (0.5L:3.5d) × 6.

2. Breeder hens fed ad libitum and subjected to either conventional or intermittent lighting ingested respectively, 25 g and 14 to 17 g more than hens restricted to 115 g/d.

3. Body weight was greater in hens fed ad libitum irrespective of the lighting pattern and of the amount of food intake.

4. Persistency of egg production was impaired by intermittent lighting.

5. Ad libitum feeding reduced egg fertility. The decrease was larger in breeder hens on intermittent lighting.

6. Hatchability was increased in hens submitted to the symmetrical lighting pattern (0.5L:3.5d).

7. Egg and chick weights were higher in hens fed ad libitum.

8. Shell index and shell breaking strength increased in restricted hens on the intermittent lighting pattern (0.5L:3.5d) × 6.

9. The best performance was obtained in restricted hens on the conventional lighting pattern.     

Genotypic differences in speed and magnitude of response to ahemeral lighting

1. The paper compares between three genetically different lines in their egg weight and shell thickness response to a 28‐h cycle.

2. The response in shell thickness to ahemeral lighting was more rapid (2.2 d) than for egg weight (4.2 d).

3. Differences between genotypes were evident in both the speed and magnitude of response.

4. Overall, egg weight and shell thickness on the 28‐h cycle were 7% and 8% greater than on 24 h.

5. The allometric increase indicates that the increase in shell weight was on average 14% more than the increase in egg weight.     

The hen's egg: Fracture of shells loaded very slowly

1. Eggs were loaded at the equator, the load on each egg increasing at a constant, low rate dW/dt in the range from 8.7 to 0.39 g/s.

2. When loading continued until shell failure the mean value of the force at failure, Pf, decreased as the loading rate decreased.

3. Among eggs from a given population the mean value of the product P_fR_a was related to log ê (dW/dt) in a linear manner, where R_a is the reciprocal of the average curvature of the shell at the point of application of the load.

4. When loading had been halted shortly before the expected time of failure, delayed failure was observed in more than a quarter of the eggs.

5. The more closely the load approximated to the expected load at failure, the shorter the delay in eggs showing delayed failure.

6. There is a risk of loss of eggs through delayed shell fracture if they are stored in stacks of trays that permit some of them to bear loads that are not large enough to cause immediate fracture but are nevertheless fairly large.     

Effect of cuticle removal on the water vapour conductance of egg shells of several species of domestic bird

1. The effect of egg shell cuticle removal, using a 14.7 mM solution of sodium hypochlorite, on the water vapour conductance of egg shells was studied in 5 species of domestic bird.

2. The water vapour conductance of fowl and Muscovy duck egg shells was not affected by the treatment.

3. Cuticle removal increased the conductance of turkey and goose shells, particularly those already relatively porous to water vapour.

4. Removal of cuticles from domestic duck egg shells increased water vapour conductance. In this case the effect was most marked for eggs with lower initial conductances.

5. The differing patterns of resistance to water vapour loss associated with egg shell cuticle are related to the ultrastructure of the cuticle itself, especially the number and size of cuticular fissures.

6. The results suggest that egg shell cuticle is a component in a series of resistances associated with the egg shell and that the use of Fick's Law is insufficient to explain water vapour diffusion across the shell.

7. Embryo survival may be improved by cuticle removal, though this may be limited to those species in which the cuticle restricts water vapour loss in initially low conductance egg shells.     

Effect of spray sanitising on hatching egg cuticle efficacy and hatchability

1. Eggs from a broiler breeder flock were sanitised using a continuous spray sanitising machine. The effect of this treatment on the ability of the cuticle to resist water and bacterial penetration was investigated throughout the production cycle.

2. The volume of water taken up by eggs that had been sanitised was significantly (P < 0.001) greater than that taken up by the control eggs. The volume of water taken up by the sanitised eggs increased as the flock age increased, whereas water uptake was maximal for the control eggs at 42 weeks of age.

3. There was no correlation between water uptake values and shell thickness or egg weight for either the sanitised or control eggs.

4. Sanitised eggs tended to dominate the “poor cuticle quality” category at all flock ages, when a subjective assessment of cuticle quality was made using the stain Edicol Supra Pea Green.

5. Egg sanitising did not affect shell reflectance values, shell thickness or the percentage of cracked shells.

6. When flock age reached 49 weeks of age, the sanitising process significantly (P < 0.001) reduced hatchability.     

Quality characteristics of quail eggs

1. An experiment was carried out with laying Japanese quail to study the influence of age on their egg quality.

2. Egg, yolk, albumen and shell plus membrane weights increased, whereas the egg shape, specific gravity and shell thickness decreased between 49 and 154 days of age.

3. Yolk, albumen and shell plus membrane comprised 32–59%, 53–57% and 7–80%, respectively of the total egg weight.

4. Regression between the quail's age and the characteristics of eggs were derived and correlation coefficients ranged from —0–42 to — 0–86. The albumen weight was more highly correlated with egg weight than yolk weight.

5. Relationships were also derived between egg shape and specific gravity, and egg shape and albumen weight.

6. It was concluded that the eggs’ characteristics were modified as the quails aged, and the best criterion of the shell's strength was the egg shape.     

Studies on egg shell strength,shell stiffness,shell quantity,egg size and shape

Physical properties which included shell stiffness, egg weight, width and length, shell weight and thickness, percentage shell, shell weight per unit area, shape index and roundness were studied in relation to maximum force and energy absorbed at failure in 2733 eggs produced by sixty SCWL pullets. Pooled‐egg, bird‐average and individual‐bird bases were used for correlation and regression analyses.

All physical properties in combination accounted for 61.9 and 88.2 per cent of the variation in force and 19.6 and 59.5 per cent of energy absorbed at failure in pooled‐egg and bird‐average analyses respectively. The non‐destructive measurements of shell stiffness, egg size and shape gave R ² values of 60.5 and 86.9 per cent with force and 16.2 and 55.0 per cent with energy in corresponding analyses.

Shell stiffness proved to be the most important predictor of force at failure. Analyses in which variation of shell stiffness was explained by other physical properties supported the conclusion based on theories of elasticity applied to shell structures that shell stiffness was largely an indirect measurement of egg shell quantity together with lesser effects of egg size and shape.

Bird‐to‐bird variation in relations between physical properties and shell strength was evident from individual bird analyses. Coefficients of determination from force at failure regressed on shell stiffness had a mean value of 0.455 with a standard deviation of 0.178 (n = 60).     

Physical characteristics of intact and cracked eggs

1. Six egg samples, comprising equal numbers of intact and cracked eggs, were collected from three flocks of hybrid layers.

2. Cracks were classified according to type (hole, star or straight) and the weight, shape, shell colour and specific gravity of all the eggs were measured. Shell thickness and dry shell weight were also recorded for a maximum of 10 intact and 10 cracked eggs from each sample.

3. The largest proportion of cracks were holes.

4. Differences in mean egg weight and shape of intact and cracked eggs within each sample were inconsistent. Mean shell colour was darker for the intact brown eggs than for the cracked ones. For all the samples, mean egg specific gravity, shell thickness and dry shell weight were higher for the intact eggs. The difference in egg specific gravity was significant (P<0.05) for all samples.

5. Holes occurred in eggs of lower mean weight but with better quality shells than those in which star or straight cracks occurred.     

The hen's egg: Shell cracking at impact on a heavy,stiff body and factors that affect it

1. Eggs from hens of three strains were dropped on to a heavy, stiff, smooth, plane body with impact at the equator of the shell; the height of drop, h_c, just sufficient to produce shell failure was measured and the corresponding impact velocity, v_c, calculated.

2. A small but commercially important percentage of the well‐formed eggs of one strain cracked when h_c was as low as 3–3 mm and v_c 250 mm/s.

3. Characteristics of the egg found to affect h_c and v_c included the overall thickness of its shell, thickness of its weak inner shell layer and average shell curvature, all measured at the point of impact, and its weight; its age also had a small effect (additional to that mediated through loss of weight); so did the degree of shell ridging.

4. No effect of shell colour was found.

5. Shell damage was typically a single hair‐crack that ran either round the equator or towards a pole.     

Traits influencing the hatching performance of Japanese quail eggs

1. Japanese quail eggs from moderately heavier sires showed superior fertility; while fertile eggs from moderately heavier dams hatched slightly better than the eggs from lighter dams.

2. Higher rates of fertility and hatchability of Japanese quail eggs were observed from parents of 10 to 19 weeks of age, with peak fertility and hatchability at 14 and 12 weeks of age, respectively.

3. Sex ratios of 1:2 to 1:5 gave comparable fertility and hatchability results.

4. The hatching performance of quail eggs from cage and deep litter reared breeders was comparable.

5. Fertility and hatchability were directly proportional to the egg weight.

6. Quail egg shell colour, tints and blotches were found to influence hatching performance.

7. Storing quail eggs at 16 ± 2°C and 75 ± 5% relative humidity for more than 4 d reduced hatchability.

8. Hatchability of eggs stored at room temperature was improved if they were sealed in polyethylene bags.

9. Provision of light during the first 14 d of incubation resulted in a photo‐acceleration of about 3.2 h.     

Relationships between age,shell quality and individual rate and duration of shell formation in domestic hens

1. The duration and rate of shell formation was measured individually in each of 44 hens. Comparisons were made between hens of different ages, and also between hens which laid eggs of differing shell qualities.

2. Shell formation began 9–5 to 11 h after the oviposition of the previous egg, increased linearly for 13 h and then plateaued at 1–5 h before oviposition.

3. The variation in egg shell quality observed in two experimental groups of hens was 75% attributable to differences in the rate of shell deposition and 25% attributable to difference in the duration of shell deposition.

4. The mean interval between ovipositions increased with age but neither shell weight, nor rate or duration of shell depositon were affected. The increase in egg weight with age accounted for the decrease in shell quality.

5. Intervals between ovipositions were positively correlated with the duration of shell formation, especially its latter stages.

6. Egg production was negatively correlated with the interval between ovipositions but not with the duration or rate of shell deposition. There was a negative correlation between duration and rate of shell deposition, except in the case of the hens producing eggs of poor shell quality.     

Studies on the avian shell gland during egg formation: Aqueous and electrolytic composition of the mucosa 1

1. The intracellular composition of the avian shell gland mucosa was studied at six stages of egg formation.

2. Total water content of the mucosa before shell calcification was 4.8 kg/kg dry weight (dw) and rose to 6.6 kg/kg dw during shell formation; 60% of the increase was intracellular and 40% extracellular.

3. The potassium concentration of the mucosa remained constant during egg formation.

4. Chloride was removed constantly from the mucosal cells during egg formation.

5. A model was constructed for the glandular cells which depicts them as primarily NaHCO₃‐secreting cells towards the luminal side and HC1‐secreting cells towards the serosal side, their main function being to provide CO^2‐ ₃ for shell formation. In this model, the columnar mucosal cells are responsible for the calcium used in shell formation.     

Eggshell of the domestic guinea fowl

1. Physical characteristics of eggs of the domestic guinea fowl, Numida meleagris galeata, were measured and compared with those of its wild counterpart and with other birds using allometric relationships.

2. The shell thickness increased and the area density of pores decreased from the blunt to the pointed end of the egg. During incubation, shell thickness decreased, but the shell diffusive conductance to water vapour (G_H2O) remained constant.

3. Fresh egg mass (m₀), length and breadth of the egg, G_H2O and specific water vapour conductance, spG_H2O (G_H2O per g of m₀ ), were affected by the age of the laying flock.

4. Eggs of the domestic guinea fowl were bigger and heavier than eggs of the wild one.

5. Allometry showed that guinea fowl eggs differ from those of the other birds by their greater shell thickness and density of pores. However spG_H2O was normal, the thickness of the shell being compensated for by a greater density of pores for gas exchanges.     

The importance of convection in the determination of the water vapour conductance of avian egg shells

1. It was confirmed that convection across the avian egg shell surface does not affect diffusive transport of water vapour through the shell.

2. Relative water vapour conductance, i.e. the ratio between the water vapour conductance as determined in a desiccator and the actual water vapour conductance, as well as relative humidity in the desiccator are influenced by the total rate of water loss of the eggs in the desiccator.

3. The total rate of water loss is influenced by the number of eggs in the batch, their average actual water vapour conductance, desiccator temperature and barometric pressure.

4. Therefore water vapour conductance is easily underestimated, in particular when determined in still air at a small surface area of desiccant.

5. All the above effects are considerably reduced by convection.

6. Further improvements in technique are suggested, particularly for practice where determinations have to be made for a relatively large batch of eggs.