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Variation in the ovarian and plasma progesterone and estradiol levels of the domestic hen during a pause in laying

100%

Proszkowiec M. , Rzasa J.

Folia Biologica

2001

tom 49

nr 3-4

285-289

Little is known about the physiological events occurring in the chicken ovary during a pause in laying, therefore the aim of the present study was to examine changes in sex steroid concentration in the follicle wall and blood plasma during cessation of egg laying. The experiment was performed on laying Isa Brown hens. Control hens were fed ad libitum whereas the experimental ones were subjected to a pause in laying by complete food deprivation for 5 days and water deprivation on 3 day followed by feeding every second day up to 9 day and then ad libitum. Blood samples were taken from the wing vein each day. The hens were decapitated on day 3, 6, 9, and 16. The ovary was isolated and the following follicles were dissected: white (1-2; 2-4; 4-6; 6-8 mm) and yellow preovulatory ones (F1-F3). Progesterone and estradiol were measured in the follicle wall and blood plasma by RIA methods. The hens stopped egg laying on day 4 and began egg restoration on day 14 of the experiment. Cessation of egg laying was preceded by a decrease in estradiol and progesterone levels in the ovary as well as in the blood plasma. The plasma level of these steroids began to increase 7 days before the start of egg restoration. Autopsy of the ovary showed that the atrophy of the chicken yellow preovulatory follicles during the pause in laying was accompanied by a significant increase in the total number of white follicles.

Estimation of genetic parameters for monthly egg production in laying hens based on random regression models

100%

Wolc A. , Szwaczkowski T.

Journal of Applied Genetics

2009

tom 50

nr 1

41-46

. Heritability and genetic correlations of monthly egg production under random regression models were estimated. Three layer lines (A22, A88, K66) in six consecutive generations were analysed. A22 (13,770 recorded hens) and A88 (13,950 recorded hens) are maternal lines of Rhode Island White birds selected on egg production and shell colour; K66 (9,351 recorded birds) is a paternal line of Rhode Island Red birds selected on egg weight. Eight models with different orders of Legendre polynomials were applied. Adequacy of the models was checked by the Akaike Information Criterion. According to the most adequate model including second order Legendre polynomials for fixed effects and third order for additive genetic and permanent environmental effects, relatively high heritabilities were estimated in the first (h2=0.3) and final (h2 above 0.3) periods of production with a substantial decrease in heritability during the egg production peak. Methodology based on random regression animal models can be recommended for genetic evaluation of laying hens.

Simulation study on the application of Gibbs sampling for major gene detection in a population of laying hens

100%

Szydlowski M. , Szwaczkowski T.

Journal of Applied Genetics

1998

tom 39

nr 4

321-330

A method for the detection of segregating major genes based on the analysis of estimated marginal posterior major gene variance density was examined. The properties of the method were investigated using data sets simulated for a real population of laying hens consisting of eleven generations. Marginal posterior densities of model parameters were estimated by the Gibbs sampling approach proposed by JANSS et al. (1995). With the data of about 4000 observations it was possible to detect a major gene responsible for one third of the genetic variance and one tenth of the phenotypic variance, irrespectively of the degree of dominance at the major locus. The inference based on the posterior marginal major gene variance can be sensitive to skewness of the data. It was shown that skewness of 0.2 can lead to a false detection of a major gene. The method is robust against a non-genetic mixture of normal distributions.

Chromosomal abnormalities in early embryos and commercial chicks and hatchability in reproduction flocks of layer and broiler hens

75%

Jaszczak K. , Jaszczak J.

nr 3

287-293

The frequency of chromosomal abnornalities in 16-18 hour embryos and one-day commercial chicks from parental flocks of layer (Astra S) and broiler (Astra B) hens as well as results of fertilization and hatchability in these flocks were compared. A karyotype analysis of Astra S showed that 6.5% of the embroys and 2.6% of the chicks were with chromosomal abnormalities. In the flock of Astra B hens only 3.0% of the embryos and 1.1% of the chicks had abnormal karyotype.Triploidy and chimerism were the most frequently identified abnormalities in both Astra A and Astra B flocks. No significant differences in the frequency of particular types of chromosomal aberrations were found between Astra S and Astra B flocks, except translocation and which were observed only among Astra S hens. The percentage of hatchability from set and fertile eggs in Astra S flock was 80.5 and 84.8 and that in Astra B was 84.3 and 88.3, respectively. The revealed differences in the frequency of chromosome aberrations and in the hatchability between the studied flocks of layer and broiler hens may result from genetic make-up of the strains and lines utilized for production of cross-bred chicken, such as the parental stocks of Astra S and Astra B.