The action of sulphanilamide on shell deposition

1. The action of sulphanilamide on egg shell deposition has been studied in the domestic fowl. The length of time that eggs remain in the shell gland was measured; the relative thickness and protoporphyrin pigment concentration for egg shells removed from the shell gland were determined; egg shell structure was examined using a replica technique.

2. Sulphanilamide appeared to act mainly by reducing the rate of shell deposition, time spent in the shell gland was unaffected.

3. The thickness of shell components was reduced in a roughly proportional manner in thin shells produced during sulphanilamide treatment.

4. It is proposed that other thin shells in which the component layers are all reduced to a similar extent are also the result of a decreased deposition rate.     

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.     

Effect of strain and age on the relationship of oviposition time to shell strength

1. The relationships between oviposition time and specific gravity, shell thickeness, deformation and breaking strength of eggs from six commercial layer strains were examined after 6 and 12 months of production.

2. Shell strength, assessed by any of the methods, was relatively low in eggs collected at 10.00 h and was generally successively greater in those collected at 12.00, 14.00 or 16.00 h. Over the same period egg weight decreased.

3. These time‐related changes in shell strength were similar for the two production ages despite the difference in shell quality due to age.

4. No consistent significant differences were observed between strains in time of oviposition.     

The hen's egg: Evidence on the mechanism relating shell strength to loading rate

1. The decrease in strength of an egg shell which is known to accompany an increase in the period of time over which a load is applied might come about by either of two mechanisms: a decrease in the strength of the material constituting the strong, outer layer of the mineral shell, or a decrease in the thickness of this layer brought about by deepening of the crevices that are normally present between adjacent crystal columns in the weak, inner layer of the shell.

2. Experiments designed to discriminate between these mechanisms are described: the results indicate the second mechanism.

3. This mechanism offers explanations for various other shell phenomena, including delayed fracture under a static, cyclical or recurrent load.

4. The main implication for the poultry industry is that any external insult to a shell is likely to weaken it by doing damage that is local, internal, irreparable and cumulative, even though it may be invisible from the outside.     

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.     

Responses of the reproductive vascular system during the egg‐formation cycle of unanaesthetised laying hens

1. Vascular adjustments to the process of egg formation were examined in the unanaesthetised laying hen, by the radioactive microspheres method.

2. Three‐ to four‐fold increases in blood flow were found in segments surrounding the egg during its passage along the oviduct, possibly due to an enhanced metabolic activity in the muscle layer of the oviduct.

3. Shell‐gland blood flow was minimal in the absence of an egg and increased gradually to a maximum (5‐fold) about 5 h after entrance of the egg into the shell gland. This parallels the rate of calcification of the egg shell.

4. Changes in blood flow in the ovarian follicles and other parts of the oviduct were small while the egg was in the shell gland. This might be typical for the reproductive system of the fowl, which undergoes little structural alteration during egg formation.     

Studies on the avian shell gland during egg formation: The effect of acetazolamide on the composition of the mucosa

1. The effect of acetazolamide, an inhibitor of carbonic anhydrase activity, on the intracellular composition of the shell gland mucosa was determined.

2. The normal cyclic hydration of the mucosal cells was found to be reduced when the egg was in the uterus and the partition of the water between the intra‐ and extracellular compartments was modified.

3. Acetazolamide decreased the accumulation of Na+ within the cells, inhibited the Na+‐independent movement of Cl‐ and reduced the transfer of Cl‐ linked with Na+.

4. It is concluded that acetazolamide blocks the intracellular generation of HGO₃‐ and the reabsorption of Cl‐.     

The hen's egg: Relationship of mean strain energy at shell fracture to shell compression speed,the nature of the compressing body and the location on the shell of the point of contact

1. The mean energy, E_f, required for fracture of an egg shell at its equator by a flat plate is known to depend on shell compression speed, v_m, for speeds in the range 20 μm/s to 2.lb5 mm/s; analysis of published data shows that E_f bears a linear relationship to log (v_m ) throughout the industrially important speed range from 20 μm/s to 1.lb1 m/s, increasing from 1.lb3 to 5.lb0 mJ.

2. At lower speeds down to 2 μm/s E_f is constant.

3. E_f is reduced if the flat plate is replaced by a sphere or cylinder; the greater its curvature, the smaller E_f.

4. E_f for the narrow pole is greater and for the broad pole smaller than that for the equator but these differences may be due in part to . systematic differences in shell thickness as well as curvature.     

The formation of mineral and organic matrix of fowl cortical and medullary bone during shell calcification

45Ca and [3H]‐lysine were injected into laying fowls up to 15 h after the start of shell calcification. The birds were killed 3 h later and the isotopes assayed in extracts of the medullary and cortical fractions of the tibias and femurs.

It was found that medullary bone is extensively resorbed and resynthesised during egg shell calcification. It is maximally loaded with calcium about 8 h after the initiation of calcification. Cortical bone, on the other hand, is inert relative to medullary bone but may be resorbed during the early stages of shell calcification, probably providing some calcium for medullary synthesis.

The absolute amounts of both types of bone were not found to vary during the egg‐laying cycle.     

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).     

Interrelationships between shell quality and egg production and egg and shell weights in white leghorn and white rock hens

Interrelationships between shell quality, production rate, egg and shell weights in relation to seasonal changes were compared in White Leghorn (WL) and White Rock (WR) hens. An increase in the average egg weight was observed in both breeds during the hot summer months. The weight and quality of the shell decreased gradually in eggs laid by WL hens, but increased in those from WR during the summer.

Significant negative correlation coefficients were found between shell quality and egg weight in only the WL, when analysed on the basis of individual averages for the entire experimental period and on weekly averages for the breed. No significant correlation was found between shell quality and production rate in WL hens. Great variabilities were obtained between individual birds regarding the correlations between shell quality and egg weight and between shell quality and production rate, when calculated on the basis of seasonal changes in both breeds.

Multivariate analysis, in which shell quality was correlated with the other variables in all combinations possible, supplied a wider explanation than the simple correlations calculated.

The differences between the two breeds are discussed.     

The effect of water on egg shell strength including a study of the translucent areas of the shell

A series of measurements of egg shell strength was carried out, using a needle to pierce the egg at a number of points at the waist up to a maximum of eight.

It was found that water weakens the egg shell whether it gets in from the outside of a normal egg or from the inside of an emptied egg. This weakening caused by water is not permanent and the shell recovers its strength on drying in air. Absolute alcohol strengthens the empty shell even more than air‐drying, but not to the same extent as oven‐drying. Shell strength slowly increases when a normal egg is allowed to stand in the air for a month.

Translucent areas of the shell are weaker than opaque areas and this difference is more marked at a week old than in a newly laid egg. Soaking the shell in water weakens it but also eliminates the difference between the two types of area, while oven‐drying strengthens the shell but also eliminates the difference.

The possible relationship of these points to the more practical aspects of shell strength and to the accurate measurement of shell strength is mentioned.     

Relationship of plasma calcium and phosphorus to the shell quality of laying hens receiving saline drinking water

1. From 36 to 43 weeks of age 210 White Leghorn laying hens were used to study the relationship of plasma calcium and phosphorus concentrations to egg‐shell quality when saline drinking water was given.

2. Seven experimental treatments in which different amounts of sodium chloride were supplied by the food and/or the drinking water were compared.

3. Increasing salt intake through the drinking water or the food reduced shell thickness and shell calcium, and increased the numbers of damaged eggs. Sodium chloride given in the drinking water was more effective in reducing shell quality and increasing plasma calcium and phosphorus than sodium chloride given in the food.     

A study of the mechanical properties of egg shell

1. The mechanical behaviour of the egg shell of the domestic fowl was investigated by cutting strips from the shell and testing the flection either in a four‐point load test or in a cantilever beam test.

2. It was found that moisture content, temperature and load rate have important effects on shell properties ; both the strength and stiffness of the shell are greater in snapping‐inward tests than in snapping‐outward tests; residual stress exists in the egg shell; the correlation between failure moment and shell thickness was highly significant, on average about 0.9, and was dependent on the spread in the thickness data.

3. Estimates were made of the ultimate strength and Young's modulus of egg shell material and it is concluded that a substantial size effect exists in the egg shell.     

Expression of TRPV6 and CaBP-D28k in the egg shell gland (uterus) during the oviposition cycle of the laying hen

1. The aim of this study was to investigate the localisation of the transient receptor potential vanilloid channel type 6 (TRPV6) in egg shell gland (ESG) and examine the dynamic expression of TRPV6 and Calbindin-d28k (CaBP-D28k), as well as the changes in concentration of total calcium (Ca), total inorganic phosphorus (P), alkaline phosphatase (ALP), parathyroid hormone (PTH) and calcitonin (CT) in plasma during the oviposition cycle.

2. The plasma ALP activity was notably increased at 8 h. In addition, plasma CT was highest at 0 h and significantly lower at 8 h. The change of plasma PTH concentration increased slightly post-oviposition and reached a maximum at 16 h.

3. Immunohistochemical analysis indicated that TRPV6 was strongly localised to the apical luminal epithelium of the mucosa. The mRNA levels of TRPV6 and CaBP-D28k in the ESG remained very low from 0 to 4.5 h, but were significantly increased at 16 h. Furthermore, Western blotting analysis showed that the expression of TRPV6 and CaBP-D28k also reached a maximum at 16 h and was different from the concentration of CaBP-D28k.

4. In conclusion, the epithelial Ca²⁺ channel TRPV6 is strongly expressed in the epithelial cells of the eggshell gland, and the increase of TRPV6 and CaBP-D28k mRNA and protein expression during eggshell formation suggests that active Ca²⁺ transcellular transport exerts significant effects in delivering active calcium in the ESG.     

Time relationships between oviposition,ovulation and egg formation in khaki campbell ducks

1. Ten‐month‐old Khaki Campbell ducks were killed between 5 min and 15 h after oviposition. Time of oviposition and interval between eggs were recorded prior to killing.

2. Oviposition generally occurred between 04.00 and 06.00 h, 7 to 9 h after the onset of the dark period the previous day. Ninety‐seven percent of eggs were laid by 07.00 h.

3. The mean ± SD time interval between consecutive ovipositions was 24.0 ± 0.3 h, with a range from 23.5 to 24.5 h.

4. It was estimated that ovulation occurred on average 10 min after oviposition, and the ovum spent 15 to 30 min in the infundibulum, 2.5 to 3 h in the magnum, 2 to 2.5 h in the isthmus and 18.6 h in the shell gland.     

Influence of dietary osteolathyrogens on the ultrastructure of shell and membranes of eggs from laying hens

1. Laying hens were fed osteolathyrogens, either semicarbazide hy‐drochloride at 0.3 g/kg or β‐aminopropionitrile fumarate at 0.6 g/kg, to examine their effects upon the ultrastructure of shell and shell membranes by scanning electron microscopy.

2. Effects of the 2 lathyrogens were similar. Compared with the highly‐branched network of fine fibres in normal membranes, there is widespread lack of separation of fibres in lathyritic specimens and hence, uneven distribution of nucleation sites. Pores are also uneven in size and distribution, which can account for increased permeability.

3. Establishment between shell and membranes is reduced. Within the cone layer both type A and type B mammillary bodies occur. Large interstitial spaces and late fusion of the palisade layer indicate reduced resistance to fracture.     

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.     

Egg‐shell deposition and blood plasma inorganic phosphorus concentration in individual laying hens

1. The relationship between plasma inorganic phosphorus measured at the end of the dark period and the weight of the next egg shell produced was investigated in 30 Hisex Brown hens.

2. Hens received an adequate conventional layers’ diet and the lighting pattern was conventional (17 L:7 D). Observations were made early (31 to 40 weeks) and late (62 to 68 weeks of age) in the laying period.

3. Eggs were classified by position in the clutch sequence and significant negative correlations were found between shell weights of early eggs in the sequence and plasma phosphate at the end of the dark period.

4. No significant trends were found in plasma total calcium.

5. No significant differences were found in bone compositions of birds producing consistently more or less than average shell weight during the laying period.

6. The negative correlations between plasma phosphate and shell weight are consistent with the observations of Sauveur and Mongin (1983) and show that impairment of shell deposition is associated with skeletal mobilisation as indicated by increase in plasma phosphate. This is consistent with the observations on bone composition and indicates that selection for shell quality will tend to select birds which are not dependent on excessive skeletal mobilisation during shell formation.     

The use of selection and strain crossing to reduce egg shell breakage

1. Selection for low egg shell deformation and high egg production was carried out in two White Leghorn strains, M and H, in order to test the feasibility of reducing the incidence of egg breakage without loss in egg production.

2. Selected and control lines were maintained within each strain.

3. After three generations of selection, egg shell deformation was reduced in the M selected line as compared to its control counterpart but this change in deformation was not accompanied by a reduction in egg breakage; however, no reduction in deformation or egg breakage was achieved in the H selected line.

4. Crossing the M and H strains resulted in a reduction of egg breakage in the crosses as compared to the average breakage of the parental strains, suggesting the potential of utilising strain crosses to reduce the incidence of egg shell breakage.