The effect of mild inbreeding in two lines of White Leghorn

1962 ◽  
Vol 13 (2) ◽  
pp. 362 ◽  
Author(s):  
JA Morris
Keyword(s):  
Egg Production ◽  
Adult Stage ◽  
Random Mating ◽  
Continuous Selection ◽  
Differential Sensitivity ◽  
Time Of Death ◽  
White Leghorn ◽  
The Mean ◽  
Selection For ◽  
June July

The reaction of two flocks of White Leghorn to slow inbreeding has been examined. One flock, the M line, has been subject to continuous selection for egg production or an associated character since 1947, and the other, the C line, has been propagated by means of random mating without artificial selection for a corresponding period. Mean inbreeding, as measured by Wright's coefficient (F), increased steadily in both flocks to reach a maximum of 25.1% in the M line and 16.2% in the C line. Significant intra-year regressions of survivors' production (72 weeks), hatchability of fertile eggs, and egg production during the winter months of June–July, on computed F values, were observed for both lines. In addition, significant regressions for the 72-week production index, age at first egg, and pauses during June–July were observed for the M line. Viability of chickens, both during early rearing (hatching date to 3½ weeks of age) and during adult stage (approximately 20 weeks to 72 weeks of age), was not affected by small changes in degree of inbreeding. Intra-year regressions on F of age at death and production up to time of death were non-significant for both lines. Highly significant differences between yearly regressions of egg production, and pauses during the two winter months, on F values were observed. These differences could indicate a differential sensitivity of response to inbreeding associated with seasonal adversity. It was not possible to substantiate the existence of a differential response to a stress factor when mortality during a severe heat wave was examined, as the mean computed F value of birds dying was not significantly greater than the corresponding F value of survivors. The stress was reasonably severe, as 15.4% of all birds died within a couple of days.

Continuous selection for egg production using short-term records

1963 ◽  
Vol 14 (6) ◽  
pp. 909 ◽  
Author(s):  
JA Morris
Keyword(s):  
Genetic Correlation ◽  
Egg Production ◽  
Continuous Selection ◽  
Total Production ◽  
White Leghorn ◽  
Short Term ◽  
Selection For ◽  
Residual Performance ◽  
Actual Response ◽  
Selection Differentials

A closed flock of White Leghorn has been selected for high egg production, since 1947. Selection has always been based on performance achieved from date of first egg until May 31 (part-period test). Selection has been effective in providing gains of approximately three eggs per generation for the part-period and, at the end of the experiment, there is no evidence that the rate of gain has lessened. Total 72-weeks egg production increased during the earlier years of selection but seems to have plateaued subsequently. This leveling off of total production is due to a decline in performance for the period June 1 to 72 weeks of age. The magnitude of this decline is sufficient to offset the gain in the part-period. Annual selection differentials were calculated for the later years, and generally the realized selection differentials were the same size as that intended, which indicated that natural selection was not opposed to the direction of artificial selection. The estimates of heritability of part-period production index show no decline as a result of selection; the actual response observed during the last years of selection supports the contention of absence of such a decline. Although it cannot be statistically confirmed, there are indications that the genetic correlation between part-period and residual performance has decreased in value with the progression of selection. The size of the correlated decline in the residual production suggests not only a reduction in value of the genetic correlation but also a change of sign. The results obtained imply that continuous selection, based on egg production for the part-period, may be an unrewarding procedure; and that selection based on other characters, favourably correlated genetically with total production, might be more effective in providing genetic gain in total production.

Genetic parameters associated with characters effecting egg production in the domestic fowl. I. Heritability of total egg production during the pullet year

1956 ◽  
Vol 7 (6) ◽  
pp. 625 ◽  
Author(s):  
BL Sheldon
Keyword(s):  
Standard Error ◽  
Domestic Fowl ◽  
Egg Production ◽  
Genetic Parameters ◽  
Research Centre ◽  
Narrow Sense ◽  
White Leghorn ◽  
Components Of Variance ◽  
Production Index ◽  
The Mean

Egg production records of White Leghorn pullets hatched a t the Poultry Research Centre, Werribee, Vic., during 1947 to 1950 inclusive have been analysed both on a hen-housed (Production Index) and a survivor basis. Estimates of heritability were obtained by two methods: (1) by the analysis of components of variance between families of full sibs and half-sibs; (2) by estimating the intra-sire regression of the mean performance of offspring on dam's performance. Heritability, in the narrow sense, of Production Index during the pullet year is shown to be 23-30 per cent. with a reasonably low standard error, while heritability of survivors' production is slightly lower but not significantly so. Possible reasons are advanced for the low estimates of heritability of survivors' production.

The influence of population density on the number of eggs laid by females of Cardiaspina albitextura (Psyllidae)

1963 ◽  
Vol 11 (2) ◽  
pp. 190 ◽  
Author(s):  
LR Clark
Keyword(s):  
Egg Production ◽  
Adult Stage ◽  
Limiting Factor ◽  
Severe Damage ◽  
Population Densities ◽  
Experimental Conditions ◽  
Nymphal Development ◽  
The Mean ◽  
Peak Abundance ◽  
Oviposition Sites

Field observations and experiments suggest that crowding during the period of nymphal development does not greatly affect the mean number of eggs laid by Cardiaspina albitextura females. Under experimental conditions, crowding in the adult stage on foliage undamaged by nymphs resulted in reduction of the mean number of eggs laid, the supply of favourable food being probably the limiting factor. In association with increase in the number of adults per shoot, mean egg production declined at a progressively decreasing rate. At the highest population densities tested, the mean number of eggs laid per female was approximately one-third to one-fifth of the number laid by uncrowded females. Both at low and high population densities, the mean number of eggs laid per female on previously unoccupied foliage was about twice as high as on foliage which had been occupied previously by numerous other adults of the same psyllid generation. At times of peak abundance in areas of outbreak, the foliage damage caused during the period of nymphal development greatly limits both the quantity of favourable food and the number of oviposition sites available when C. albitextura reaches the adult stage. The experimental results suggest that the crowding of adults which occurs on the small amount of foliage that escapes very severe damage by nymphs contributes towards the observed limitation of egg production. However, the scattered distribution of such foliage and the poor dispersal powers of C. albitextura females probably play a more important part in determining the very low mean number of eggs laid per female reaching the adult stage. It appears that many females fail to find favourable foliage and consequently lay scarcely any eggs.

XI.—An Investigation into the Effects of Seasonal Changes on Body Temperature

1913 ◽  
Vol 32 ◽  
pp. 110-135 ◽  
Author(s):  
Sutherland Simpson
Keyword(s):  
Body Temperature ◽  
Rectal Temperature ◽  
Egg Production ◽  
Weather Conditions ◽  
Barometric Pressure ◽  
Temperature Curve ◽  
The Body ◽  
The Mean ◽  
One Year ◽  
June July

SummaryMonthly observations, extending over one year, were made on the rectal temperature of 114 domestic fowls (Gallus gallus, ♀) and records from forty-one of these were obtained for two years. Six different breeds were used, each located in a separate pen, all under similar conditions, and the mean temperatures for each group were plotted out to form an annual temperature curve. It was found that—1. The lowest temperatures occur in December, January, and February, and the highest in June, July, and August, corresponding in a general way with the temperature of the external air.2. Barometric pressure does not appear to have any influence on the body temperature of the hen.3. The curve of egg-production does not coincide with the annual temperature curve, the former reaching its highest level in April and May, the latter in June, July, and August.If we compare the mean rectal temperature at two periods of the year when the external or weather conditions are approximately the same (April-May and September-October), but when the vitality of the birds, as indicated by the curve of egg-production, moulting, etc., is at a maximum and minimum respectively, we find that the figures are practically identical. This would seem to show that cyclical bodily changes have little effect on body temperature as compared with outside influences.

FERTILITY OF BARLEY AUTOTETRAPLOIDS: II. THE RELATIONSHIP OF ANEUPLOIDY, DWARFING AND FERTILITY IN FOUR AUTOTETRAPLOID BARLEY VARIETIES

1961 ◽  
Vol 41 (1) ◽  
pp. 124-133 ◽  
Author(s):  
E. Reinbergs ◽  
L. H. Shebeski
Keyword(s):  
Continuous Selection ◽  
The Other ◽  
High Fertility ◽  
Chromosome Distribution ◽  
Apparent Relationship ◽  
Identical Number ◽  
The Mean ◽  
Selection For ◽  
Relationship Of ◽  
The Relationship

A considerable number of dwarf plants (16.4 to 85.7 per cent) was found in C2 to C5 generations of four artificially-induced barley autotetraploids from the varieties OA.C. 21, Brant, York and Montcalm.The Montcalm tetraploid, which was the lowest in mean fertility, had the highest percentage of dwarfs. In the other three tetraploids there was no apparent relationship between the frequency of dwarfs and the mean per cent fertility. In the O.A.C. 21 tetraploid continuous selection for plants with high fertility did not reduce the occurrence of dwarfs.Most of the dwarf plants were aneuploids with 26, 27, 29, 30 or 31 chromosomes, but plants with identical number of chromosomes often showed differences in phenotype. Among the aneuploids 29-chromosome plants were most frequently found. The 26- and 31-chromosome plants were completely sterile. Only a low percentage of the other aneuploid plants produced seed. By considering the observed percentages of dwarf plants and the ratio of hypoploids to hyperploids produced, the largest part of sterility in the four barley autotetraploids could be attributed to irregular chromosome distribution.

Sire × hatching season interaction in egg production traits within flocks of domestic fowl

1979 ◽  
Vol 30 (5) ◽  
pp. 991
Author(s):  
BH Yoo ◽  
BL Sheldon
Keyword(s):  
Domestic Fowl ◽  
Variance Component ◽  
Egg Production ◽  
Production Traits ◽  
White Leghorn ◽  
Egg Weight ◽  
Sib Families ◽  
Selection For ◽  
Efficiency Of Selection ◽  
Season Interaction

The extent of sire x hatching season interaction in egg production characters has been studied in White Leghorn, Australorp and Synthetic flocks in which half-sib families bred from the same sires were mated largely to the same dams for spring and autumn hatchings. Interaction appeared to be more important in White Leghorn and Synthetic than in Australorp. The estimate of variance component for interaction was not consistent among the three flocks, and it was important only in certain flocks for different characters: age at first egg, part-annual hen-housed production (PHP), and egg weight at 34 and 62 (EWL) weeks of age in Synthetic; and annual survivors' production and egg specific gravity at 62 weeks of age (SGL) in White Leghorn. Comparison of within-season and across-seasons heritabilities showed that the former could be on average more than 45% higher than the latter in PHP, EWL, SGL and annual hen-housed production. As the estimates of the genetic correlation coefficient between seasons tend to be below 1.0 for many characters in White Leghorn and Synthetic, the sire x hatching season interaction may need to be taken into account and investigated further to improve the efficiency of selection for egg production.

scholarly journals Keel bone fractures are more prevalent in White Leghorn hens than in Red Jungle fowl hens—A pilot study

PLoS ONE ◽  
2021 ◽  
Vol 16 (7) ◽  
pp. e0255234
Author(s):  
Käthe Elise Kittelsen ◽  
Pall Gretarsson ◽  
Per Jensen ◽  
Jens Peter Christensen ◽  
Ingrid Toftaker ◽  
...  
Keyword(s):  
Pilot Study ◽  
Egg Production ◽  
Laying Hens ◽  
Bone Fractures ◽  
Laying Hen ◽  
White Leghorn ◽  
Red Jungle Fowl ◽  
White Leghorns ◽  
Selection For

Fractures and deviations to the keel bone are common in commercial laying hens, with reported variations in occurrence across strains and breeds. The aetiology is not fully understood, however, modern genetics and selection for efficient egg production has been claimed to be important factors for the keel bone fractures. To explore this further, we investigated keel bones from two different breeds, representing different degrees of selection for egg production: Red jungle fowl (n = 82), and White Leghorn (n = 32), where the latter is a selected laying breed which is the origin for many modern laying hen hybrids. Keel bones from a total of 116 birds, 53 hens and 63 roosters, were examined by necropsy at 80 weeks of age. All birds were raised in modified aviaries in the same holding facility. Overall, 24.5% of the hens had one or more fractures to the keel, with a difference in the prevalence between hens from the two breeds (p<0.01): 10% (95% CI: 3.7–24%) in the Red Jungle fowl hens and 69% (95% CI: 37–90%) in the White Leghorn hens. No roosters, regardless of breed, had keel bone fractures. Mild to moderate keel bone deviations were present in 54% (95% CI: 25–80%) of the hens and 4.7% (95% CI: 0.5–30%) of the roosters, all White Leghorns.

scholarly journals No evidence that selection for egg production persistency causes loss of bone quality in laying hens

2021 ◽  
Vol 53 (1) ◽  
Author(s):  
Ian C. Dunn ◽  
Dirk-Jan De Koning ◽  
Heather A. McCormack ◽  
Robert H. Fleming ◽  
Peter W. Wilson ◽  
...  
Keyword(s):  
Rhode Island ◽  
Bone Quality ◽  
Egg Production ◽  
Breaking Strength ◽  
Genetic Correlations ◽  
Egg Laying ◽  
White Leghorn ◽  
Medullary Bone ◽  
Selection For

Abstract Background The physiological adaptations that have evolved for egg laying make hens susceptible to bone fractures and keel bone damage. In modern laying hen breeds, longer periods of egg laying could result in a greater risk of poor bone quality, and selection for increased egg production has frequently been stated to be a cause. However, the existing literature does not support this hypothesis. To test the hypothesis that egg production is associated with quality, breaking strength and density of bone, genetic correlations between these traits were estimated in White Leghorn and Rhode Island Red breeds. Genetic correlations of cortical and medullary bone material chemical properties with bone quality were also estimated, in order to identify methods to improve bone quality with appropriately targeted measurement of key traits. Results Estimates of heritability for bone quality traits were moderate (0.19–0.59) for both White Leghorn and Rhode Island Red breeds, except for the keel bone trait, which had a heritability estimate equal to zero. There was no evidence for genetic or phenotypic relationships between post-peak egg production and bone quality. In the White Leghorn breed, the estimate of the genetic correlation between pre-peak production/age at first egg and bone quality was significant and negative (− 0.7 to − 0.4). Estimates of heritability of thermogravimetric measurements of tibial medullary bone mineralisation were significant (0.18–0.41), as were estimates of their genetic correlations with tibia breaking strength and density (0.6–0.9). Conclusions The low genetic correlation of post-peak egg production with bone quality suggests that selection for increased persistency of egg production may not adversely affect bone quality. Onset of puberty and mineralisation of the medullary bone, which is a specialised adaptation for egg laying, were identified as important factors associated with the quality of the skeleton later during egg production. These are traits for which genetic, as well as environmental and management factors can positively impact the overall quality of the skeleton of laying hens.

scholarly journals INFLUENCE OF B LOCUS BLOOD GROUPS ON ADULT MORTALITY AND EGG PRODUCTION IN THE WHITE LEGHORN CHICKEN

Genetics ◽  
1973 ◽  
Vol 75 (1) ◽  
pp. 181-189
Author(s):  
A W Nordskog ◽  
W A Rishell ◽  
D M Briggs
Keyword(s):  
Natural Selection ◽  
Blood Group ◽  
Egg Production ◽  
Adult Mortality ◽  
Blood Groups ◽  
White Leghorn ◽  
White Leghorn Chicken ◽  
B Locus ◽  
Selection For ◽  
Relative Spread

ABSTRACT The influence of the B locus blood group on adult viability and egg production was studied in two White Leghorn populations (S1 and S2) synthesized from inbred line crosses. Each line segregated for four B alleles. Four homozygotes and six heterozygotes were produced in each line over a five-year period, and for an additional three years tests on certain blood-group combinations were continued. A total of 4371 birds were included in the study. Greatest differences in blood groups were found in the S1 line, with the B2 and B21 alleles seemingly having favorable effects and with B1 having unfavorable effects. The B1 homozygote was consistently the lowest in egg production (53.2%) and highest adult mortality (40.4%). The relative spread in standard deviation units between the B1 and B2 homozygotes was more than three times greater in adult mortality than in egg production; B2 was incompletely dominant to B1. Within the S1 line, the superiority of the heterozygotes was mainly a consequence of the poor fitness of the B1 homozygote, suggesting that in a random-mated population B1 would be maintained only by mutation and not by a polymorphic mechanism.—Over the eight years of the experiment, adult viability of the B1 homozygote improved 4.4% per year (P&lt;0.05). Assuming this regression results from natural selection, either of two hypotheses can account for the results: (1) The B locus is pleiotropic with natural selection for many B modifiers, and (2) the B locus is neutral but linked to a major fitness locus.

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