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1.
1. More than 9000 eggs, each laid by a known hen, were examined and malformations of six types recorded: double‐yolked, A, B, rough, shell‐less and thin‐shelled.

2. A and B malformations are those seen in, respectively, an egg that is held in the shell gland for an abnormally long period and one that reaches the shell gland while an A‐egg is still there; many of the eggs recorded as rough‐shelled were probably A‐eggs for which the corresponding B‐eggs had been lost.

3. The birds were of three strains: a medium‐body‐weight brown‐egg‐laying strain and a White Leghorn strain, both of commercial origin, and a laboratory strain of Brown Leghorns.

4. The incidences of egg malformation in the three strains were 8.3, 9.2 and 0.5%.

5. A‐, B‐ and rough‐shelled eggs constituted more than two‐thirds of all malformed eggs.

6. Evidence from two generations suggests that these malformations have a high heritability.  相似文献   


2.
1. Genetic parameters and responses to selection involving egg composition and allied traits were estimated, using two unselected control strains and three selected strains of White Leghorns.

2. Heritability estimate for yolk weight was 0.5 ± 0.1; for albumen percentage protein, 0.6 ± 0.1; and for yolk percentage solids, 0.5 ± 0.1.

3. Genetic correlation estimates indicated that there was no antagonistic relationship between the weight of any egg component and its composition but, because of the unreliability of the estimates of the genetic correlations involving the egg number traits, it is impossible to predict the correlated effects that selection for egg composition would have on egg number.

4. Eggs from selected strains weighed an average of 3‐. g more, contained more albumen, and greater amounts of albumen percentage solids and percentage protein than controls, whereas no differences were found for yolk weight; yolk percentage solids changed little in the selected strains.

5. Comparisons of one control strain with four commercial strains suggest that the findings may be applicable to commercial stocks.  相似文献   


3.
The occurrence of a crack in an egg shell depends in part on the local strength of the shell, which in turn depends on its curvatures as well as its thickness, and therefore on its shape. Selection for shell shape is therefore needed; but before the breeder can do this he must have a rapid and accurate method of quantifying shell shape, and knowledge of the factors that affect its variation.

A procedure is described whereby nine measurements of an egg shell—length, maximum breadth, distance from the plane of maximum breadth to the broad pole and the distances by which each pole projects into annuli of diameters 1.5, 2.5 and 3.5 cm—are used to obtain an equation describing the profile of the egg in polar coordinates. It has five parameters that measure, independently, five shell characteristics: scale, aspect (breadth‐to‐length ratio), skewness, marilynia (concordant bulging between the poles and the plane of maximum breadth) and platycephaly (discordant bulging). Egg volume and superficial area can be obtained by integration, shell curvatures by differentiation. An experiment in which the computed volumes of 61 eggs from 19 hens of four strains were compared with the volumes measured by water displacement failed to detect, in single‐yolked eggs, any discrepancy not attributable to random measurement error, which was 0–2 per cent of mean egg volume.

Aspect, marilynia and platycephaly are shown to be correlated inter se and with egg size; differences between hens and strains in respect of them are shown to exist. Making the shell measurements could be automated and use of the method could lead to improved efficiency of selection for egg size as well as shape.  相似文献   


4.
The heritabilities of and genetic correlations between part record production, body weight, egg weight, shell colour, specific gravity and albumen quality have been estimated in one strain each of Light Sussex and Rhode Island Red and in three strains of White Leghorns using variance and covariance components in a hierarchical classification.

The heritability values are in general agreement with published figures. Because of the wide variation in the size of the variance components no valid conclusions about the effects of sex linkage, dominance or maternal effects can be drawn from this type of analysis.

Significant positive genetic correlations exist between: egg weight and body weight in four strains; egg weight and shell colour in one strain; body weight and Haugh units in one strain; specific gravity and Haugh units in one strain, and a negative correlation exists between body weight and shell colour in one strain.

Because of the difference in genetic correlations, selection is thought likely to have a rather different outcome on the characters in each strain and stress is laid on the need to calculate genetic parameters separately for each strain.  相似文献   


5.
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6.
The influence of two diets, differing only in their phosphorus content, on egg shell thickness was compared in 24 pullets in a change‐over experiment lasting 8 weeks. The mean shell thickness of the eggs laid on the low‐phosphorus diet (0.46 per cent total phosphorus) was 2 per cent greater than the mean thickness expressed interms of mg./cm.2 on the high‐phosphorus diet (1 per cent total phosphorus), and this difference was statistically significant. It is suggested that the increase in shell thickness on the low‐phosphorus diet was due to increased absorption and retention of dietary calcium, but this suggestion could not be confirmed experimentally in two balance periods of 6 days each owing to the great variations in calcium retention observed both between and within birds. The skeletal weights of birds killed after laying for approximately 11 months on one or other of the two rations showed no correlation between dietary treatment and skeletal weight, percentage egg production or mean shell thickness.  相似文献   

7.
A variety of methods exists for assessing egg shell strength. For practical field use, a method is desired which is relatively rapid, easy to use and cheap. It must demonstrate differences between experimental varieties or nutritional treatments with sufficient precision that decision makers can rely on the results. A study has been made of eggs from 10 inbred lines of White Leghorns using non‐destructive deformation, beta backscatter count, deformation at failure, force at failure, shell stiffness and shell thickness to estimate shell strength.

A comparison of these methods indicated that under the conditions of this experiment, backscatter count yielded low coefficients of variation and did not demonstrate differences between inbred lines. The other methods showed differences between lines with non‐destructive deformation possessing an acceptable combination of precision, ease of operation and cost. Deformation and force at failure and egg shell stiffness required expensive non‐portable apparatus but stiffness was nevertheless thought to be a useful parameter. Direct measurement of shell thickness was acceptable but necessitated breaking the eggs.  相似文献   


8.
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).  相似文献   


9.
Percentage weight loss on ashing was measured in 110 shell segments: 4 segments per shell—broad polar cap, narrow polar cap and two halves of the “barrel” —from 28 shells from 4 strains of chicken. The membranes had been removed, by hand, from each shell segment and shell thickness measured with a biconvex anvil micrometer. For each segment the function γ = T (1 + Wodm/Wmdo) was calculated, where T is the mean thickness, Wo the weight loss upon ashing, Wm the ash weight, d0 the density of the organic matter in the shell (assumed to be 1.0075 g/cm3) and dm the density of the mineral matter (2.386 g/cm3). Govariance analysis of the regression of T on T for each shell segment within each strain showed that the regression was linear, that the lines did not differ in slope, but that there were significant differences between the adjusted means for strains and for segments. This is interpreted as demonstrating that (a) the amount of organic matter in incremental shell is constant, estimated at 0.68 per cent by weight, and (b) the amount of organic matter outside incremental shell is variable. The equivalent thickness of the latter was estimated for each segment of each shell with a standard deviation of 0.4 μm. Other evidence suggests that the variation in organic matter outside incremental shell is due mainly to variation in cuticle thickness. Implications for poultry breeding and for future research are discussed.  相似文献   

10.
1. Egg production of four‐way crosses of seven commercial stocks of White Leghorns was summarised for each hen into 28‐d periods starting from the day of first egg.

2. The exponential models of McMillan and of Wood and a linear regression were fitted to the results for individual hens, as well as to the mean results for periods of groups of hens.

3. Overall, the McMillan model gave the best results with mean R2 of 0.71 from fitting it to the results for 223 individuals with sixteen 28‐d periods each and R2 of 0.97 from fitting it to the period means for groups. The respective R2 values were 0.68 and 0.95 for the Wood model and 0.60 and 0.90 for the linear regression.  相似文献   


11.
1. Egg shell cracks and body checking were assessed on a total of 25 776 eggs collected from 744 hens of two selected White Leghorn strains between 65 and 72 weeks of age.

2. The sire‐component heritabilities in the two strains, respectively, were 0–59 ± 0.23 and 0.36 ± 0.20 for total cracks and 0.41 ± 0.20 and 0.49 ± 0.22 for body checking. The heritabilities for hole, star and hair cracks ranged from ‐0.03 ± 0.13 to 0.66 ± 0.24.

3. The frequency of total cracks did not bear any significant antagonistic relationship with body checking, egg number and egg weight. Body checking had variable relationship with egg number and egg weight. The correlations of shell cracks and body checking with each other and with egg number and egg weight appeared to vary between the strains.  相似文献   


12.
Experiments are described from which it is concluded that the shell will split when an egg is boiled if thermal expansion of the egg's liquid or gaseous contents, which have a higher coefficient of expansion than the shell, is insufficiently relieved by escape through the membranes and pores. The probability of splitting was enhanced if the shell had low structural strength due to a pre‐existing crack or to large size, skew shape or low effective thickness; once these factors had been taken into account there was no significant effect of the shell's aspect ratio, colour, glossiness, roughness or degree of ridging, nor of the hen's age or a strain history of selection for egg production. The incidence of splitting depended also on storage time and temperature: it was very low in newly laid eggs; in eggs stored at room temperature it rose to a maximum at about 5 d, then fell and was again low after about 21 d; in eggs stored at — 2 °C the time‐scale was increased and the incidence of splitting was still high after 14 d storage. These effects are due to two changes occurring during storage: progressive reduction of permeability of the membranes and shell to the liquid contents of the egg, which impedes escape of the contents when they expand during cooking, and progressive increase in the size of the air space, which provides expansion space. Allowing refrigerated eggs to warm to room temperature before cooking and adding salt to the cooking water did not significantly affect the incidence of splitting; putting eggs into cold rather than boiling water did not reduce the incidence of splitting except when the air space was large, following prolonged storage at room temperature.

The belief, common among housewives, that shell splitting occurs more commonly now than in earlier decades may be well‐founded but, if so, the change is probably due to a combination of two practices that have been introduced to maintain interior egg quality but which coincidentally raise the probability of shell‐splitting during boiling: rapid distribution from hen to housewife and refrigerated storage. There is no evidence that shells are now thinner, that hens of modern, high‐production strains lay eggs with weaker shells or that white shells are weaker than brown ones.  相似文献   


13.
Measurements of specific gravity, egg weight and albumen height of eggs from three consecutive trap days were taken at approximately 225, 350 and 450 d of age, for three years, from three strains of the White Leghorns. Haugh units were calculated for each egg. From these data estimates of genetic parameters were derived.

Pooled estimates within the 27 strain‐period‐year subclasses for heritability of single egg records from sire components of variance for specific gravity, egg weight, albumen height and Haugh units were 0.36, 0.48, 0.46 and 0.45, and repeatability within periods for the four traits were 0.68, 0.74, 0.76 and 0.74 respectively. The intra‐class correlations (repeatabilities) between period‐means of the same hen expressed in standard deviation units for each subclass were 0.58, 0.71, 0.74 and 0.69 respectively. Genetic correlations between adjacent periods were high varying from 0.91 to 0.96 while those between non‐adjacent periods varied from 0.76 to 0.87 for the four traits.

It was suggested from the size of these estimates that annual performance for a quality trait could be improved by selecting pullets on the basis of a small number of egg measurements taken at early periods in the laying year.  相似文献   


14.
Experiments are described from which it is concluded that

  1. the force required to shear egg shell material can be measured with high precision by pressing a narrow, flat‐ended plunger on to the shell;

  2. shearing force falls and the precision of its measurement rises as the radius of the plunger is reduced;

  3. shearing force is related linearly to shell thickness ;

  4. the regression line of shearing force on shell thickness does not pass through the origin but has a substantial positive intercept on the thickness axis, at about a third of the mean thickness ;

  5. there are differences between hens and between strains of hen in the magnitude of the intercept, but not in the slope of the regression;

  6. shearing force is affected also by the glossiness of the shell;

  7. shearing force was not significantly affected by stripped membrane thickness, number of mammillae per unit area of shell, shell organic content (standardised for shell thickness), shell curvature, shell colour, mottling score, translucent patch score, speckling score, age of the egg or age of the hen that laid it;

  8. measured with a plunger of radius 165 μm, the mean shearing strength of incremental shell was 57 kg wt/mm2 (3–7 ton/in2).

The findings suggest that the shearing strength of egg shells might be increased by direct selection and by selection for shell glossiness.  相似文献   


15.
1. Shell superficial area (S, mm2) and volume (V, mm3) of an egg can be estimated from any one or a combination of the following measurements: fresh egg weight (W, g), shell length (L, mm) and maximum shell breadth (B, mm).

2. Estimation equations and their error standard deviations are given.

3. The random error of the estimate is smallest when estimation is based on L, B and W together: 0.4% for S and 0.6% for V.

4. Estimation of S based on L and B together has the advantage over that based on W alone that it is unnecessary to measure the egg soon after lay; the random error is the same (0.7%).  相似文献   


16.
Six blocks of data are analysed: British Egg Marketing Board (BEMB) data on second quality eggs‐in‐shell in packing station throughput; shell thickness and colour data on 1,440 eggs sampled in 4 packing stations; crack incidence data on 162,480 individually recorded eggs from a two‐strain experimental flock kept in battery cages; similar data on 34,611 eggs from another experimental flock; shell thickness, volume and shape data on 76 eggs from 19 pairs of hens, one of each pair with a high and one with a low shell‐crack record; and BEMB data on the prevalence of battery and deep‐litter husbandry. Conclusions reached are:

  1. Over the last decade there has been a rise in the incidence of packing‐station egg downgrading in the United Kingdom; it is assumed to have been due largely to a rise in the incidence of cracked shells.

  2. The rise in crack incidence was probably not due primarily to deterioration in shell strength associated with high production rates or white shell colour; such associations were looked for but not found.

  3. It was probably due primarily to an increase in “ environmental insults “ to packing‐station eggs accompanying the spread of deep‐litter and battery husbandry; a close association was found between their incidence and that of downgrading.

Implications for cage designers, breeders, egg producers and research workers are discussed.  相似文献   


17.
In a group of birds of the same breed, those laying eggs with the thinnest egg shell membranes (mg/cm2) were the most likely to produce corrugated shells. Furthermore, in series of eggs from individual birds, an increase in the degree of corrugation of the shell was accompanied by a thinning of the shell membrane as well as an increase in egg weight. Given the presence of a thin membrane, the greater the weight of the egg the greater was the chance that it would have a corrugated shell.

Corrugations result from the deposition of shell on a corrugated membrane which is possibly caused by insufficient plumping of the egg or by the presence of weak areas in the membrane becoming distorted under pressure.  相似文献   


18.
1. Egg‐shell colour, egg specific gravity, shell thickness and egg weight were determined for 2080 eggs from three varieties of the Vasca, a Spanish brown‐egg‐laying hen.

2. Intermediate, positive and significant (P < 0·01) correlation coefficients were found between egg‐shell colour and specific gravity (0·25), or shell thickness (0·21). There was a very high (0·84), significant (P < 0·01) correlation between the measures of shell strength.

3. Shell thickness was accurately predicted with both specific gravity and egg weight as independent variables (determination coefficient 0·74); eggshell colour did not explain any further variation.

4. All traits showed considerable departure from normality in the form of negative kurtosis (shell colour and specific gravity), positive kurtosis (shell thickness and egg weight), negative skewness (shell thickness) or positive skewness (egg weight).

5. Egg‐shell colour, specific gravity and shell thickness were less in July, in old birds and in eggs laid in the morning. Differences in egg quality traits between the three varieties were not significant.

  相似文献   

19.
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.  相似文献   


20.
1. Experiments with eggs from fowls of three strains failed to support a breeder's belief that the sex of a chick could be predicted from the position of the air space relative to the axis of the egg.

2. Relative to sex found at dissection, the accuracy of sexing newly hatched chicks by endoscope was 98% and by head markings (in Brown Leghorns) 88%.  相似文献   


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