Changes in body and organ weights of Japanese quail selected for 6‐week body weight 1

Three populations of Japanese quail, selected over 13 generations for increased body weight, a randomly selected base population and reciprocal backcrosses of selected lines to the control were studied. Live body weight and weights of liver, testes, oviducts and carcasses were obtained to assess the effects of selection.

At 6 weeks of age a 20 g. difference in live body weight existed between selected line and base population. Sexual dimorphism in live body weight in favour of females appeared at 3 weeks of age and increased with age. A 5 g. difference in 6‐week body weight between female backcross progeny from sires from selected lines and those sired by males from the base population suggested an influence of sex‐linked genes. At 8 weeks of age the weight of females of both reciprocal back‐cross types significantly exceeded the average of females from the selected lines suggesting that female reproductive organ weight had increased under selection as well as heterosis. Carcass weight of selected females was lower than for corresponding males, a reversal of the sexual dimorphism displayed by the controls.

Reciprocal differences in liver weight between backcross females, but not males, suggested an effect of sex‐linked genes.

Testis as well as oviduct weights of quail from selected lines were substantially greater than from controls.     

Selection with restriction in a poultry breeding scheme with different selection procedures in both sexes: Correlated responses

1. Mass selection in two replicate lines of Leghorn chickens was practiced for low 20‐week body weight in males and by an index designed to reduce age at first egg, body weight at 20 weeks and maintain a constant early egg size in females.

2. Selection responses in body weights of hens at 40 and 60 weeks of age, as well as in average egg weight of all eggs, egg number, egg mass and feed conversion at the above ages are given for 5 generations of selection.

3. Estimation of genetic responses were made separately for selection on males (M _i ) and females (F _i ) using control groups of hens from matings between females with an index near the population average and either males with body weight near the population average (Cl) or the selected males within lines (C2).

4. Total genetic response to selection of both parents (CR _i ) showed an expected decline in body weights of hens, small changes in egg weights and egg numbers, and an improved feed efficiency.     

Genetics of changes in economic traits during the laying year

Body weights, egg weights and egg numbers were measured at different ages in two distinct, fully pedigreed, random bred strains of White Leghorns over a period of 3 years. The heritabilities of the separate measurements and the genetic correlations between them were obtained by an analysis of variance and covariance. The principal findings were:

(i) The heritability of weight gain declined sharply with age over consecutive periods after 12 weeks. The genetic correlation of body weight at 12 weeks with gain in subsequent periods was low. There appeared to be sufficient genetic variance in growth rate in these later periods to alter the growth curve substantially by selection. For example, it should be possible to breed strains with a rapid early growth and low mature body size.

(ii) There was evidence of genetic variation in the change of egg weight with time. The genetic variation was, however, so low that in any selection programme to improve 28‐week egg weight without changing 44‐week egg weight the progress would be very slow.

(iii) Body weight at 12 weeks was genetically negatively correlated with sexual maturity. Its correlation with production in the first 44 weeks was positive in both strains, but not significantly different from zero.

(iv) Body weights after 28 weeks were apparently uncorrelated with egg production or sexual maturity.

(v) Egg weight and production traits show considerable heterogeneity of variance between years, probably partly due to their distribution not being normal.

(vi) The pattern of genetic variation appeared to differ significantly between the two strains so that correlated responses would not necessarily be the same.

(vii) There was a suggestion of maternal effects acting upon body weight but the evidence was somewhat contradictory and inconclusive due to the high standard error of the estimates.

(viii) None of the 15 traits measured regressed over the 3 year period of relaxation of selection.     

Heritabilities and genetic correlations in related dwarf and normal broiler populations 1

1. Heritability estimates were higher for 8‐week body weight in dwarf than in normal broiler populations due to the maternal effects of dwarf dams.

2. The dwarfing gene dw did not induce new genetic variability for egg weight, 30‐week body weight and age at sexual maturation.

3. Genetic correlation estimates showed that the selection for 8‐week body weight will increase egg weight in dwarf pullets more than in normals.

4. Within a dwarf population it should be possible to increase 8‐week body weight without influencing the mature size of pullets.     

Genetic variation and phenotypic correlations of food consumption of laying hens corrected for body weight and production

1. On samples from two brown‐egg strains between 1967 and 1979, “ residual” food consumption (i.e. food consumption corrected for body weight, weight change and egg mass) of laying hens was investigated with respect to variation between sire families and phenotypic correlations with production traits, egg traits, morphological and physiological variables. A similar residual food intake (corrected for body weight and body‐weight gain) was obtained for samples of males in some years.

2. Highly significant differences between sire families were observed for residual food consumption in both strains for females and in one strain for males.

3. In females, highly significant positive phenotypic correlations were found in both populations for residual food intake with wattle length and shank temperature, and in one population with shank length and width. On the whole, a negative correlation was observed with egg‐shell thickness. For two variables recorded only in one strain, proportion of broken eggs and yolk : albumen ratio, there were highly significant positive correlations.

4. For males also, wattle length and shank temperature were positively correlated with residual food intake.

5. The physiological meaning and possible use of correlated variables as criteria for indirect selection for food efficiency of layers are discussed.     

Genetic control populations: A study of efficiency of six poultry control strains

The aim of the experiment was to examine the efficiency of pedigreed random‐bred control populations. It was argued that it was difficult to achieve this aim by the study of the parameters of a single control population, but that a comparison of the contemporaneous performance of two or more control strains over several generations would be more appropriate.

Six pedigreed randombred control populations with a planned size of 50 males and 150 females and derived from different base populations representing strains involved in a commercial poultry breeding programme were recorded for eight generations. Some difficulty was experienced in maintaining the populations to the size planned, particularly the Wyandotte strain, and this was associated with low semen production from males and low egg production from females rather than from poor fertility or hatchability. Analysis of data on sexual maturity, 25‐week body weight and 300 days’ egg production indicated no obvious regular changes in mean or variance except for sexual maturity for which the within strain variance increased markedly. The differences between strain means stayed relatively constant and there were few changes of rank order. The intra class correlation, corrected for changes in variance, for strains between years was 0–92, 1.00 and 0.96 for sexual maturity, body weight and egg production respectively.

Heritability estimates on four of the base populations indicated large differences between strains but also that additive genetic variation for some traits in some strains was approximately zero. For such traits and strains, genetic drift cannot occur which is a most desirable feature of a genetic control population. Some data were available on crosses of the control strains, which had been recorded for egg production and laying house mortality on many farms in each of eight years. There were no regular changes between years in mean egg production but mortality     

Food consumption records for the genetic improvement of income over food costs in laying flocks of white leghorns

1. A study of genetic parameters of egg mass based on the weights of all eggs laid, individual food consumption, body weight and age at first egg was made. Data from three populations differing in average egg weight were available over two production periods, from 20 to 40 and from 40 to 60 weeks of age, respectively.

2. Selection indexes designed to maximise income over food costs (IOFC) were used to evaluate the usefulness of food consumption data for the genetic improvement of laying flocks.

3. Given reliable estimates correlating food consumption to egg mass, body weights and age at first egg it is possible to construct highly efficient selection indexes for genetic improvement of IOFC without the direct use of food consumption data.

4. Selection for genetic gains in egg mass appears to be the most important factor for genetic improvement of IOFC. Correlated increases in egg weight were observed for two of the populations.

5. Body weights showed very small and inconsistent genetic responses under index selection suggesting that a reduction in body weight need not be necessary for more efficient egg production.

6. Indexes which showed greatest genetic improvement also resulted in an increase of food consumption. Thus genetic efficiency in egg laying flocks would be achieved by increasing egg mass through earlier sexual maturity, larger eggs and higher production rates with increased food consumption and only slight, if any, reduction in body size.

7. Estimates of heritabilities and genetic correlations indicate that food consumption measurements can be based on partial records; high heritabilities were found for egg mass and food consumption measurements in both early (20 to 40 weeks) as well as late (40 to 60 weeks) production periods.     

The relationship between hatching egg weight and subsequent performance of broiler chickens

Small eggs constitute a high proportion of the eggs laid by pullets. The literature shows that chick hatching weight is strongly correlated with egg weight, but evidence on the influence of egg weight on hatchability and subsequent performance of chicks is less certain.

The aim of this experiment was to determine the profit returned at 12 weeks by broiler chickens hatched from eggs ranging in weight from 44 g. to 58 g. at one gram intervals and to determine how competitive and separate rearing might modify the relationship.

A total of 6000 eggs were collected during 10 days from a 28‐week‐old, broiler breeding flock and graded into the above mentioned egg weight classes. From these, a total of 3480 day‐old broilers were housed. Each egg weight class was equally represented and balanced for sex.

Hatchability and fertility showed no consistent trend with egg weight for eggs above 46 g., but below the 47 g. level there was a trend of declining fertility and hatchability.

A strong positive relationship was found between the weight of the chick at 1 day of age and egg weight for both males and females with no significant difference overall in body weight between the two sexes.

Body weight to 12 weeks was found to be strongly related to egg weight, in a linear fashion, though this influence declined with age.

There was a greater influence of egg weight on body weight at all ages in the separate rearing treatment compared with competitive rearing but this was not significant after 10 weeks.

Egg weight had an important bearing on body weight and profit at 12 weeks, but no effect on food conversion or mortality.

The increased profit over food costs per 100 day‐old chicks was found to be 52.75 cents for the separately reared birds respectively for each 3 g. increase in egg weight.     

Changes in fitness traits associated with selection for divergence in yolk cholesterol concentration

1. Correlated changes in egg production, hatchability, egg weight, age at sexual maturation and body weight of lines selected for divergence in yolk cholesterol were studied in two different populations.

2. Divergence in yolk cholesterol resulted in a highly significant difference in percentage egg production with a negative correlation between yolk cholesterol and egg numbers. However, the calculated total daily mass of cholesterol excreted into the egg was similar in both lines.

3. These results indicate that the physiological mechanism by which these populations responded to selection pressure on the concentration of cholesterol in the yolk was by changing egg numbers rather than total amount of cholesterol excreted.

4. Body weights of the high and low yolk cholesterol lines of the meat type, but not of the layer‐type populations, were significantly different. After four generations the line selected for low yolk cholesterol from the meat‐type population weighed 80% of the line selected for high yolk cholesterol levels.

5. Sexual maturity and egg weight were also significantly different between the high and low yolk cholesterol lines, but these differences could not be related to selection response. No changes in hatchability between the cholesterol lines were observed.     

Genetic analysis of production and feed efficiency traits in an Orlopp turkey line (Meleagris gallopavo)

1. Genetic parameters for production and feed efficiency traits in the Orlopp line of turkeys were estimated to determine breeding goals and future potential of the line in a long-term genetic improvement programme.

2. Body weight, egg production and fertility traits were recorded and feed conversion ratio (FCR) was assessed from 16–20 weeks of age.

3. Moderate heritabilities were found for feed intake and body weight gain (0.25 to 0.31). Average FCR was 3.14, with heritability of 0.10. Body weight, breast conformation score and egg production traits showed moderate heritabilities (0.22 to 0.52), while both fertility and hatch of fertile eggs were low (0.04 and 0.09, respectively).

4. Genetic correlations between breast confirmation score, 10- and 18-week body weights were moderate, 0.50 and 0.45, respectively. Average egg weight also showed moderate genetic correlations with 10- and 18-week body weights (0.59 and 0.42).     

Growth and the plasma concentrations of growth hormone and prolactin in chicks: Effects of “environmental enrichment”, sex and strain

1. The effects of including novel objects in the environment ("environmental enrichment “) on body‐weight gain, relative body‐weight gain, gain : food ratio, plasma growth hormone (GH) and prolactin concentrations in male and female broiler and layer chicks was investigated.

2. Environmental enrichment improved body‐weight gain, relative body‐weight gain and gain: food ratio but had no effect on circulating GH or prolactin concentrations.

3. Weight gain and gain : food ratio were greater in the broilers than in the layer chicks, while plasma GH and prolactin (females only) concentrations were less.

4. There were no sex differences in weight gain and relative weight gain but gain : food ratio was significantly greater in females than in males. In both strains plasma GH concentrations were higher in males than in females and prolactin concentrations were higher in male than in female broilers.     

Egg production,body weight and egg quality characters; their heritability and the correlations between them

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.     

Response from selection for income minus food cost in laying hens,estimated via the animal model

1. Selection for income minus food cost between 21 and 40 weeks of age was carried out in two replicate lines of brown egg layers for 5 generations in a population derived from a commercial cross between Rhode Island Red males and White Plymouth Rock females. Each replicate and an unselected control line consisted of 20 male and 80 female breeders.

2. Egg production, egg weight and food consumption were recorded on 1200 hens in every generation. Parent females were selected on individual performance. Males were not recorded and selected at random within half sib families to minimise rate of inbreeding.

3. A linear selection response of 0.46 and 0.43 monetary units per generation was observed, which resulted in a total response of 19.8% and 18.2% of the phenotypic mean of the base population over the 5 generations. A large increase in egg weight was the most important reason for the selection response in income minus food cost.

4. Further changes in associated traits were: an increase in egg number and egg mass, and a decrease in age at first egg, body weight and food: egg mass ratio.

5. The direct and correlated selection responses were similar in both lines. The realised response was somewhat less than expected in both lines.

6. A summary of phenotypic and genetic parameters, estimated from the data, is given. All genetic correlations between income minus food cost and the associated traits analysed, were in a favourable direction.     

Estimation of combining ability in broilers from a full diallel cross

1. A 4 × 4 complete diallel cross involving four broiler strains (two of Cornish stock and two of Rock stock) was made. Twelve males from each strain were concurrently mated to three pullets from each strain in single sire pens.

2. Body weight was measured from 1‐d‐old to 10 weeks of age every two weeks in the 2880 progeny obtained in five hatches.

3. General combining ability was highly significant for all traits except body weight at 1 d old. The specific combining ability was significant for 4‐, 8‐ and 10‐week body weights.

4. Maternal effects were evident for body weights at earlier ages but gradually declined with advancing age and were non‐significant for 8‐ and 10‐week weights.

5. Sex‐linked effects, although smaller in magnitude, were evident for body weights up to 6 weeks of age.     

Response to long‐term selection for egg production in laying hens

1. A White Leghorn line was selected for part‐record hen‐housed number of eggs from 1962 to 1990. Genetic changes were estimated as deviations from its unselected control line.

2. Over the first 10 generations with selection almost exclusively for number of eggs to the age of 273 d, all traits, except rate of mortality, showed significant changes. Regressions per year were: 273 d production, 3.07 eggs; 497 d production, 5.18 eggs; production from 274 to 497 d, 2.43 eggs; age at first egg, ‐2.33 d; mean weight of first 10 eggs, ‐0.82 g; body weight at 497 d, ‐19.02 g and rate of mortality, 0.19%.

3. Over the rest of the period increasing selection pressure for egg weight has been applied. This resulted in positive changes for this trait and no or small negative changes in egg number.

4. In general, heritabilities and genetic correlations did not change over the period of selection. The heritability of the main trait of selection, production to 273 d was 0.19 ± 0.04 and heritabilities of egg size traits about 0.50.

5. The genetic correlation between egg production to 273 d and mean weight of first 10 eggs was estimated as ‐0.37 ± 0.06 but from the observed response a realised genetic correlation of ‐0.97 was calculated.     

Rearing temperature and the meat yield of broilers

1. One hundred and twenty (60 male and 60 female) 21‐d‐old Ross 1 broiler chicks were reared in cages in rooms kept at 21°C or 31°C and were killed at body weights of 1.0, 1.5, 2.0, 2.5 or 3.0 kg.

2. Birds reared at either of the two temperatures ate similar quantities of food to reach their slaughter weight although at 31°C they took longer to reach it.

3. The meat yields of the birds at each slaughter weight were similar at both rearing temperatures, but at body weights greater than 2.0 kg, the broilers reared at 21 °C had more breast meat than those reared at 31°C.

4. Females ate more food than males to reach each of the slaughter weights. The females deposited more fat and had a greater skin weight than the males and, although they had a similar amount of total meat, they had more breast meat.     

Performance of lines selected for fast‐and slow‐hatching times and crosses among them 1

1. Males of a control line and two lines selected for fast‐ and slow‐hatching were mated to females of the same three pure lines and three crosses between them. Hatchability, egg weight and hatching time were measured.

2. No significant differences were found between genetic groups in hatchability.

3. Groups containing the fast‐hatching line genotypes were significantly smaller in egg weight than those not containing this line.

4. Significant differences in hatching time existed between male lines and between female lines within pure and cross‐line parent types while no differences were observed between the female parent types and no interactions of male by female lines occurred.

5. It was concluded that inbreeding in the pure lines (10%) did not affect any of the variables measured.

6. The results on hatching time support the conclusion that little genetic variance other than additive variance is involved for this trait.     

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.     

Correlations between body measurements and tissue composition of oat-fattened White Kołuda geese at 17 weeks of age

1.?The aim of the present study was to evaluate the yield and tissue composition of carcases from White Ko?uda® ganders (males) and geese (females), and to determine the relationships between body measurements and carcase tissue composition.

2.?The experiment was carried out on 200 geese (100 males and 100 females) reared to 14 weeks of age and then fed with oats for the next 3 weeks. Live body weight and body dimensions, slaughter yield, weight and percentage of muscles and skin with fat in carcase were measured and correlation coefficients were calculated between body measurements and slaughter values and carcase tissue composition.

3.?White Ko?uda® geese reared to 17 weeks of age were characterised by high body weight (6705 g) and good muscle yield (29·9%). Males had greater body weight, musculature and fatness than females. Sternum length and breast circumference, width and depth were good indicators of carcase muscle weight in 17-week-old geese.

4.?Negative coefficients of correlation between sternum length and weight of skin with subcutaneous fat indicate that increased selection pressure in pedigree flocks of geese on sternum length should be paralleled by reduced carcase fatness in these birds.     

Genetics of hatchability and its components and some production traits of chickens 1

Twenty‐egg samples from individual pullets belonging to four closed pedigreed populations were incubated to obtain hatchability and embryo mortality data. Egg production, egg weight and body weight data were obtained from the same pullets and comprehensive variance and covariance analyses were performed on the entire body of data. A slight but consistent genetic relationship was noted between hatch‐ability and egg production, mainly due to the influence of embryo viability during the final 12 d of incubation.

Limited evidence existed suggesting negative genetic correlations between egg size and hatchability. It is suggested that this relationship may be of the curvilinear type and this is substantiated by some data from a population selected for increased egg size.

The results are discussed from the viewpoint of their possible significance in practical breeding programmes.