Genetic properties of egg quality traits and their correlations with performance traits in Japanese quail

1. Performance traits were measured on 1908 Japanese quail and egg quality traits assessed on 1800 eggs at 10?wk of age.

2. Genetic and phenotypic correlations were estimated using a bivariate animal model with restricted maximum likelihood using ASREML software.

3. Body weight at different ages showed positive genetic correlations with egg weight and most of the internal egg quality traits, whereas their genetic correlations with eggshell thickness, eggshell strength and eggshell percentage were negative.

4. Genetic correlations of age at sexual maturity and egg number with most of external and internal traits were negative.

5. It was concluded that selection for higher body weight will result in heavier and better quality eggs. Because of the negative genetic correlation between BW and egg shell quality, a selection index including BW and eggshell strength would be the best breeding strategy for genetic improvement of egg quality in Japanese quail.     

Genetic variation for egg production,egg quality and bone strength in selected and traditional breeds of laying fowl

1. A multi-breed experiment was conducted with 25 commercial and traditional lines of laying fowl to determine the extent of between-breed genetic variation for adult body weight, sexual maturity, rate of lay, egg weight and egg composition to 55 weeks of age. The genetic variability for bone strength and eggshell strength was determined at 55 weeks of age and a comparison of commercially selected and traditional breeds was performed. 2. The proportion of the total variation that was associated with breed or line of origin was high (> 0.8) for body weight, sexual maturity and shell colour; moderately high (0.4 to 0.7) for rate of lay, early and late egg weight, weights of egg yolk, albumen and shell at 55 weeks; and low (< 0.4) for egg weight at 42 to 45 weeks, albumen quality and the number of egg inclusions. 3. There were no detectable differences between breed within category (traditional and commercial lines) for rate of lay, and estimates of breed variation for egg weight and egg components were substantially decreased within category compared with the overall analysis. 4. Commercial lines displayed earlier sexual maturity, greater rates and persistency of lay, and higher egg weights at earlier (32 to 35 weeks) and later (52 to 55 weeks) ages. At 55 weeks, the larger eggs from commercial birds contained more albumen of higher quality and paler yolks of similar weight to those from traditional breeds. The relative weight of the eggshell was similar in both categories. 5. There was considerable genetic variation between commercial lines for bone density and a moderate proportion of genetic variability for bone strength. Commercial lines had very weak bones compared with traditional lines but there was relatively little genetic variation for eggshell strength. The results suggest that eggshell quality is maintained in genetically selected lines at the expense of bone strength and bone radiographic density.     

Factors affecting direct and correlated responses in a White Leghorn population under long term selection for egg number

1. Data on 13,773 pullets, the progeny of 30 to 50 sires and about 135 to 220 dams per generation of a strain of White Leghorn under long term selection for part period egg production over 16 generations, were examined. 2. Realised genetic gain per generation was highly significant for egg production (2.55 eggs), egg weight (- 0.51 g), age at sexual maturity (- 2.30 d) and 40 week body weight (- 11.73 g). 3. The significant genetic response of 4.46 to 4.72 eggs per generation was realised in the first 8 generations only, which was accompanied by a marked decline in egg weight (- 1.67 and- 0.79 g per generation) and in age at sexual maturity (- 4.63 and- 6.39 d per generation). The 20 and 40 week body weights showed significant improvement in the last 4 generations. 4. Realised heritabilities were much lower in the last 8 than in the first 8 generation. 5. The additive genetic variance for most traits, except 20 week body weight and genetic covariances of egg production with egg weight and age at sexual maturity, declined significantly. 6. Natural selection did not seem to play any major role. No appreciable change in fitness traits was observed in the selected line. 7. The time trends were non-significant for all the traits in the control line, indicating its stability over generations.     

蛋壳表型性状与蛋壳质量间的相关与通径分析

本文旨在研究蛋壳表型性状与蛋壳强度之间的相关与通径分析。试验选用40~43周龄的新鲜珍珠鸡蛋100枚,测定了其蛋重、蛋形指数、蛋壳厚度、蛋壳重、蛋壳比例、单位面积蛋壳重、蛋壳强度6个指标,计算其性状间的相关系数;采用通径分析方法计算以表型性状为自变量对蛋壳强度作因变量的通径系数、决定系数对各性状的影响大小进行分析。从通径分析结果看出,直接影响最大的是蛋壳厚度（P=0.657）,间接影响最大的是蛋壳比例（0.746）,并以蛋壳厚度指标建立回归方程为y=44.145x-9.229。在生产实践中,为获得好的蛋壳质量应着重注意蛋壳厚度和蛋壳比例,同时要协调蛋形指数、蛋重、蛋壳比例、单位面积蛋壳重与蛋壳强度之间的关系。     

Diallel cross of six long-term selected leghorn strains with emphasis on heterosis and reciprocal effects

Six strains under long-term selection for egg production and other economically-important traits were crossed in a full diallel, and tested with two commercial stocks and two control strains at two stocking rates (1 bird per 20.3-cm cage and 3 birds per 30.5-cm cage) and two diets (with and without an oyster shell supplement). The mean of the 30 strain crosses exceeded the mean of the six selected strains for egg production and egg quality traits, sexual maturity and viability, which in turn exceeded the performance of both of the control strains. The performance of several of the 30 strain crosses was similar to the commercial stocks. The only significant genotype X environment interaction was for Haugh units at 450 d. Performance at the lower stocking rate was generally superior to that at the higher stocking rate. General combining ability was important for the complete array of traits measured. Specific combining ability was important for the majority of traits. Heterosis was important for all traits except specific gravity, Haugh units, blood spots and laying house viability to 272 or 496 d at the higher stocking rate. The magnitude of heterotic effects was generally greater at the higher stocking rate. Reciprocal effects were important for egg production traits, sexual maturity, egg quality traits and viability. The dietary oyster shell supplement resulted in an improvement in shell quality as measured by specific gravity.     

Inbreeding and inbreeding depression on reproduction and production traits of White Leghorn lines selected for egg production traits.

1. The rate of inbreeding and its effect on reproduction and egg production traits were studied in White Leghorn lines selected for egg production traits. The experiment was carried out for 10 generations in a control line (C) and in lines selected for increased egg number (EN), egg weight (EW) and egg mass (EM). 2. Data were available on reproduction traits, such as percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent hatched of total eggs set (PHT), and on egg production traits such as age at 1st egg (AFE), egg number and egg weight. 3. The rate of increase in average inbreeding per generation was 1.50, 1.24, 1.14 and 0.18% for the line EN, EW, EM and C, respectively. The effect of inbreeding on reproduction and production traits was estimated by including the inbreeding coefficient of the hen (Fh), embryo (Fe) and mate (Fs) as a partial linear regression in the model. 4. There was a significant effect of inbreeding on reproduction traits in line EW attributable to the inbreeding of the hen, embryo and mate. No such effect was observed in the other lines. 5. In all lines inbreeding tended to reduce egg number and delay sexual maturity. In general, all lines reacted differently to inbreeding.     

Genome‐wide association study for egg production and quality in layer chickens

Discovery of genes with large effects on economically important traits has for many years been of interest to breeders. The development of SNP panels which cover the whole genome with high density and, more importantly, that can be genotyped on large numbers of individuals at relatively low cost, has opened new opportunities for genome‐wide association studies (GWAS). The objective of this study was to find genomic regions associated with egg production and quality traits in layers using analysis methods developed for the purpose of whole genome prediction. Genotypes on over 4500 birds and phenotypes on over 13 000 hens from eight generations of a brown egg layer line were used. Birds were genotyped with a custom 42K Illumina SNP chip. Recorded traits included two egg production and 11 egg quality traits (puncture score, albumen height, yolk weight and shell colour) at early and late stages of production, as well as body weight and age at first egg. Egg weight was previously analysed by Wolc et al. ( 2012 ). The Bayesian whole genome prediction model – BayesB (Meuwissen et al. 2001 ) was used to locate 1 Mb regions that were most strongly associated with each trait. The posterior probability of a 1 Mb window contributing to genetic variation was used as the criterion for suggesting the presence of a quantitative trait locus (QTL) in that window. Depending upon the trait, from 1 to 7 significant (posterior probability >0.9) 1 Mb regions were found. The largest QTL, a region explaining 32% of genetic variance, was found on chr4 at 78 Mb for body weight but had pleiotropic effects on other traits. For the other traits, the largest effects were much smaller, explaining <7% of genetic variance, with regions on chromosomes 2, 12 and 17 explaining above 5% of genetic variance for albumen height, shell colour and egg production, respectively. In total, 45 of 1043 1 Mb windows were estimated to have a non‐zero effect with posterior probability > 0.9 for one or more traits.     

Genetic parameters of cross‐ and purebred poultry

Heritabilities were estimated from sire and dam components for egg production traits in four generations of two pure‐lines and their reciprocal crosses. Heritabilities in cross‐breds, as estimated from the sire components of variance, were larger than in pure‐breds for production and sexual maturity. Heritabilities estimated from dam components were larger than the sire estimates, thus indicating the presence of maternal and/or dominance effects. Again, heritabilities in cross‐breds were larger than in pure‐breds for production and sexual maturity as well as for specific gravity. Heritabilities were also estimated for disease traits in material from one generation. Cross‐line values were as large or larger than those estimated from pure‐lines but the standard errors of the estimates were quite large.

Genetic correlations were estimated between pure‐line and cross‐line performance using both sire and dam covariances. These approached unity for body weight, egg quality traits and adult mortality but were considerably less than unity for production, sexual maturity, blood spots and mortality during growth and mortality due to Marek's disease.

The possible bias due to genotype x environment interaction is discussed and it is concluded that such a bias, if present, is small, and that in spite of possible G × E interaction effect the genetic correlations between pure‐line and cross‐line performance for production and sexual maturity are less than one. The same holds true of mortality during growth and to Marek's disease although these estimates are much less precise.

The genetic correlation between pure‐breds and cross‐breds appears to decrease over the span of the five generations.

Use of cross‐line performance will permit more efficient selection for traits when the genetic correlations are much less than one.     

Inbreeding and heterosis effects on quantitative traits in a White Leghorn population under long-term reciprocal recurrent selection

1. Inbreeding and heterosis effects for quantitative traits were estimated in two White Leghorn lines selected with reciprocal recurrent selection (RRS) since 1950. 2. Pedigreed progeny were produced from full-sib, half-sib and unrelated pure line as well as reciprocal cross line matings to estimate inbreeding and heterosis effects "within sires". 3. Inbreeding effects estimated as linear regressions agreed well with estimates considering inbreeding as fixed effect. The inbreeding depression per 10% inbreeding was highest for hatchability (6-7%), intermediate for production-related traits (3%), and about 1% for shell quality, body weight and egg weight. 4. Heterosis effects were estimated by comparing pure line and cross line progeny of the same sires. 5. Results indicate considerably less heterosis for egg production than found earlier, which is interpreted as a consequence of pure line selection.     

Sire x location interactions from progeny tests in different countries

1. A total of 529 progeny arising from 19 sires, which had been selected on the basis of their daughters’ body weight (heavy, medium or light) were reared in Berlin, West Germany and Kuala Lumpur, Malaysia to test for sire x location interactions for production and egg composition traits.

2. Highly significant sire x location interactions were found for sexual maturity, egg production, egg weight, food consumption and egg mass.

3. For egg composition traits, significant interactions were found in some but not all periods for shell breaking strength and albumen : yolk ratio.

4. Highly significant location effects were found for all traits studied except sexual maturity, whereas significant sire effects were found mainly for the productive traits, shell breaking strength and albumen : yolk ratio.     

Long-term goose breeding for egg production and crammed liver weight

1. Results of an 8-year (1981 to 1988) period of breeding geese for egg production and crammed liver weight, including phenotypic and/or genetic parameters for various traits (1982 to 1985), as well as line tests (1987 to 1988), are summarised for two lines. 2. The regressed annual genetic gains over years were 2.7 eggs and 30.8 g crammed liver. However, there was a decline in the rate of genetic progress after 4 years of selection. 3. Heritability estimates were found to be relatively high for most traits, whereas phenotypic and genetic correlation coefficients between traits were rather low, as would be expected from lines not previously subjected to an intense selection programme. 4. Phenotypic correlation coefficients between part-period records and full-period egg production, suggest that 3-month (October to December) records may be adequate to identify most of the best first-year layers. However, sexual maturity should be treated as a separate trait. 5. The cross between the 'Grey' (male) line, superior in crammed liver weight, and the 'White' (female) line, excelling in egg production, seems to be superior to the pure lines, in a fully-integrated enterprise.     

Relationship between egg‐shell colour and two measurements of shell strength in the Vasca breed

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.

     

A comparison of the effects of feeding treatments and lighting on age at first egg and subsequent laying performance and carcase composition of broiler breeder hens

The effects of the growth curve from 15 to 20 weeks, age at photostimulation and pattern of photostimulus on sexual maturity, egg production and egg weight were evaluated in two trials with broiler breeder females to 56 and 34 weeks of age (housed in litter pens and individually caged, respectively). Carcase composition and reproductive morphology of hens varying in laying efficiency were measured in the second trial. Trial 1: Four growth curves were applied from 15 to 20 weeks to pullets housed in litter pens. Birds were transferred from 8- to 10-h photoperiods at 20 or 24 weeks of age, followed by weekly increments of one hour to reach a 16-h final photoperiod. Lower-than-recommended body weights at 20 weeks significantly delayed sexual maturity, reduced peak rate of lay, total eggs and mean egg weight. However, double-yolked egg production was lower, resulting in non-significant differences in settable egg numbers between body weight treatments. Birds reared to the heaviest body weight exhibited a significantly advanced sexual maturity, but total egg numbers, peak rate of lay and mean egg weight were not significantly affected. However, the laying of more double-yolked eggs resulted in a decrease in the number of settable eggs. Delaying photostimulation to 24 weeks significantly retarded sexual maturity, reduced total and settable egg numbers, and increased mean egg weight. A tendency for fewer double-yolked eggs was observed. Trial 2: At 19 weeks, birds were selected from the 4 body weight categories in Trial 1 and moved to individual cages in 8 rooms. Five lighting programmes were applied. The pattern of photostimulation applied did not affect any of the production traits measured. At 34 weeks, 24 birds were selected for the analysis of reproductive morphology, presence of internal or multiple ovulations, and carcase composition. Eight hens showing an early age at first egg and regular egg production records, 8 birds showing erratic laying performance and 8 non-layers were killed for this purpose. There were no differences in carcase composition or reproductive morphology between these groups. No internal ovulations or double or multiple ovarian hierarchies were observed. The results presented confirm that broiler breeders do not require a lighting stimulus in order to initiate ovarian activity and that, where no lighting stimulus is given, body weight or feeding level plays a critical role in stimulating the birds to attain sexual maturity. However, when a lighting stimulus is given, factors such as body weight and body composition become relatively less important in regulating the age at sexual maturity.     

The hen's egg: Relationships of seven characteristics of the strain of hen to the incidence of cracks and other shell defects

1. Multiple regression and path‐coefficient analysis show that the factors with greatest influence on the incidence of cracks and other shell defects in three random‐sample tests of 47 entries of 28 strains were, in descending order, mean shell colour, mean shell thickness, mean egg production and mean egg weight, and that median age at maturity, mean body weight at 140 d and mean weight increase between 140 and 500 d had no effect.

2. Breeders who wish to exercise indirect selection for low crack incidence should consider selecting for dark shell colour rather than high shell thickness.     

Genetic study of embryonic mortality in White Leghorn lines selected for egg production traits

The present study compares embryonic mortality between lines selected for different production traits, assesses the effects of inbreeding of the hen and embryo on embryonic mortality, and estimates genetic parameters of embryonic mortality. The experiment covered 10 generations of selection for increased egg number (EN), egg weight (EW), egg mass (EM) and a control line (C). The data included age at 1st egg, egg number and egg weight. Percent fertile eggs (PF), percent hatched of fertile eggs (PHF) and percent dead chick at hatch (PDH) were also recorded for the selected parents. PDH was higher in the selected lines than in the control line. Among the selected lines, the EW line had the highest embryonic mortality. Inbreeding of the hen and embryo had no significant effect on PDH in any of the lines. Estimates of heritability for PDH were 0.10+/-0.05, 0.02+/-0.02, 0.03+/-0.02 and 0.02+/-0.02 for lines EN, EW, EM and C, respectively. There was a positive genetic correlation between egg weight and PDH in line EW indicating that selection for increased egg weight was associated with high embryonic mortality. A negative genetic correlation between PDH and reproductive traits in line EN was observed, which is favourable.     

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).     

The measurement of egg shell strength: a comparison of four methods

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.     

Heritability, genetic and phenotypic correlations of egg quality traits in Iranian native fowl

1. The objective was to estimate heritability, genetic and phenotypic correlations for egg quality traits of Iranian native fowl at the Yazd Breeding Centre. 2. External and internal egg quality traits were measured on 1200 eggs from 794 hens of the 6th generation. A multivariate animal model with restricted maximum likelihood procedure was applied to estimate heritability, genetic and phenotypic correlations for egg quality traits using ASREML. 3. Heritability estimates for external egg quality traits ranged from 0·18 to 0·57 and for internal egg quality traits from 0·24 to 0·60. 4. For external egg quality traits, genetic correlation between egg weight and eggshell thickness (EST) was positive (0·36) and EST showed high genetic correlations with eggshell weight (0·84) and eggshell strength (0·55). This implies that heavier eggs tend to have thicker and stronger shells. 5. For internal egg quality traits, albumen height showed high positive genetic correlations with albumen weight (0·52), albumen index (0·98), yolk height (0·72) and yolk index (0·57). 6. Our results show that it is feasible to improve egg quality in Iranian fowl through selection for albumen height.     

2‐Hydroxy‐4‐methylthio butanoic acid and DL‐methionine for Japanese quails in production

An experiment was performed using 1,000 laying Japanese quails to assess the availability of two alternative dietary methionine sources. Treatment 01 = Basal Feed that is deficient in digestible methionine + cystine (Met + Cys). The other treatments were constituted by Met + Cys levels of 0.8, 1.60 and 2.40 g/kg, supplemented with DL‐Methionine‐99%, HMTBA‐88% and HMTBA‐84%, being 10 treatments in total. The following characteristics were studied: feed intake (g/bird/day), egg production (egg/day × 100), egg weight (g/egg), egg mass (g/egg), feed conversion per egg dozen (kg feed/dozen eggs), feed conversion per egg mass (kg feed/kg eggs), relative yolk weight (g/100 g of egg), relative albumen weight (g/100 g of egg), relative shell weight (g/100 g of egg), shell thickness (mm) and specific gravity (g/cm³). In general result comment, supplemental methionine sources must be included in the poultry diet. The different methionine sources affect the performance of quails, and the increase in the levels within each source improves the performance variables. Significant effect was observable on performance variables and egg quality variables, being that DLM‐99% is superior to the other sources. The HMTBA‐88% source is superior to the HMTBA‐84% source for the same aforementioned variables. In conclusion, the bioefficacy values of the HMTBA‐88% and HMTBA‐84% sources compared to the DLM‐99% source on an equimolar basis were 81 and 79%, respectively, for the performance variables, and 83 and 74 while the methionine sources were equivalent for the variables related to egg quality.     

Trial for detecting carriers with major genes in a selected layer line

Production traits of a Rhode Island Red layer line were analyzed to detect carrier animals with major genes that influenced a particular trait by applying the major gene index (MGI) approach. This method was used to examine the deviation of predicted breeding values between parents and offspring. Advantages of this method include its simplicity and time‐reducing, cost‐saving benefits compared with any other statistical approach for screening major genes. The layer line had been selected based on the desired gain index for 6 years at the National Livestock Breeding Center, Okazaki station. The line consisted of 125 sires and 2986 dams. Two economic traits as breeding objectives were studied – age at sexual maturity (ASM, days) and egg production efficiency (EP, %). The MGI detected nine sires and 23 dams as carriers with major genes for ASM, and five sires and 26 dams for EP. They were identified as important breeding stock, and pedigree information provided candidates possessing major genes with favorable effect at the founding of the selected layer line. It seems likely that the simple approach of the MGI could be a useful preliminary method for detecting carrier animals with major genes before applying molecular techniques on a sampled population to identify in more detail the existence of major genes and their carriers.