Genetic parameters and principal component analysis for egg production from White Leghorn hens.

The objectives of this study were to estimate genetic parameters for accumulated egg production over 3-wk periods and for total egg production over 54 wk of egg-laying, and using principal component analysis (PCA), to explore the relationships among the breeding values of these traits to identify the possible genetic relationships present among them and hence to observe which of them could be used as selection criteria for improving egg production. Egg production was measured among 1,512 females of a line of White Leghorn laying hens. The traits analyzed were the number of eggs produced over partial periods of 3 wk, thus totaling 18 partial periods (P1 to P18), and the total number of eggs produced over the period between the 17 and 70 wk of age (PTOT), thus totaling 54 wk of egg production. Estimates of genetic parameters were obtained by means of the restricted maximum likelihood method, using 2-trait animal models. The PCA was done using the breeding values of partial and total egg production. The heritability estimates ranged from 0.05 ± 0.03 (P1 and P8) to 0.27 ± 0.06 (P4) in the 2-trait analysis. The genetic correlations between PTOT and partial periods ranged from 0.19 ± 0.31 (P1) to 1.00 ± 0.05 (P10, P11, and P12). Despite the high genetic correlation, selection of birds based on P10, P11, and P12 did not result in an increase in PTOT because of the low heritability estimates for these periods (0.06 ± 0.03, 0.12 ± 0.04, and 0.10 ± 0.04, respectively). The PCA showed that egg production can be divided genetically into 4 periods, and that P1 and P2 are independent and have little genetic association with the other periods.

Egg production curve fitting using nonlinear models for selected and nonselected lines of White Leghorn hens.

Egg production curves describe the laying patterns of hen populations over time. The objectives of this study were to fit the weekly egg production rate of selected and nonselected lines of a White Leghorn hen population, using nonlinear and segmented polynomial models, and to study how the selection process changed the egg-laying patterns between these 2 lines. Weekly egg production rates over 54 wk of egg production (from 17 to 70 wk of age) were measured from 1,693 and 282 laying hens from one selected and one nonselected (control) genetic line, respectively. Six nonlinear and one segmented polynomial models were gathered from the literature to investigate whether they could be used to fit curves for the weekly egg production rate. The goodness of fit of the models was measured using Akaike's information criterion, mean square error, coefficient of determination, graphical analysis of the fitted curves, and the deviations of the fitted curves. The Logistic, Yang, Segmented Polynomial, and Grossman models presented the best goodness of fit. In this population, there were significant differences between the parameter estimates of the curves fitted for the selected and nonselected lines, thus indicating that the effect of selection changed the shape of the egg production curves. The selection for egg production was efficient in modifying the birds' egg production curve in this population, thus resulting in genetic gain from the 5th to the 54th week of egg laying and improved the peak egg production and the persistence of egg laying.

Estimation of genetic parameters for partial egg production periods by means of random regression models.

We estimated genetic parameters for egg production in different periods by means of random regression models, aiming at selection based on partial egg production from a generation of layers. The production was evaluated for each individual by recording the number of eggs produced from 20 to 70 weeks of age, with partial records taken every three weeks for a total of 17 periods. The covariance functions were estimated with a random regression model by the restricted maximum likelihood method. A model composed of third-order polynomials for the additive effect, ninth-order polynomials for the permanent environment, and a residual variance structure with five distinct classes, was found to be most suitable for adjusting the egg production data for laying hens. The heritability estimates varied from 0.04 to 0.14. The genetic correlations were all positive, varying from 0.10 to 0.99. Selection applied in partial egg production periods will result in greater genetic profit for the adjacent periods. However, as the distance in time between periods increases, selection becomes less efficient. Selection based on the second period (23 to 25 weeks of age), where greater heritability was estimated, would note benefit the final egg-laying cycle periods.

Estimates of genetic parameters, and cluster and principal components analyses of breeding values related to egg production traits in a White Leghorn population.

The objectives of this paper were to identify the phenotypic egg-laying patterns in a White Leghorn line mainly selected for egg production, to estimate genetic parameters of traits related to egg production and to evaluate the genetic association between these by principal components analysis to identify trait(s) that could be used as selection criteria to improve egg production. Records of 54 wk of egg production from a White Leghorn population were used. The data set contained records of the length:width ratio of eggs at 32, 37, and 40 wk of age; egg weight at 32, 37, and 40 wk of age; BW at 54 and 62 wk of age; age at first egg; early partial egg production rate from 17 to 30 wk and from 17 to 40 wk of age; late partial egg production rate from 30 to 70 wk and from 40 to 70 wk of age; and total egg production rate (TEP). The estimates of genetic parameters between these traits were estimated by the restricted maximum likelihood method. Multivariate analyses were performed: a hierarchical cluster analysis, a nonhierarchical clustering analysis by the k-means method of weekly egg production rate to describe the egg-laying patterns of hens, and a principal components analysis using the breeding values of all traits. The highest heritability estimates were obtained for BW at 54 wk of age (0.68 ± 0.07) and age at first egg (0.53 ± 0.07). It is recommended that a preliminary clustering analysis be performed to obtain the population structure that takes into account the pattern of egg production, rather than the TEP, because hens may have the same final egg production with different patterns of egg laying. Early partial production periods were not good indicators for use in improving total egg production because these traits presented an overestimated genetic correlation with TEP because of the part-whole genetic correlation component. Egg production might be improved by selecting individuals based on TEP.

Comparison of logistic and neural network models to fit to the egg production curve of White Leghorn hens.

Neural networks are capable of modeling any complex function and can be used in the poultry and animal production areas. The aim of this study was to investigate the possibility of using neural networks on an egg production data set and fitting models to the egg production curve by applying 2 approaches, one using a nonlinear logistic model and the other using 2 artificial neural network models [multilayer perceptron (MLP) and radial basis function]. Two data sets from 2 generations of a White Leghorn strain that had been selected mainly for egg production were used. In the first data set, the mean weekly egg-laying rate was ascertained over a 54-wk egg production period. This data set was used to adjust and test the logistic model and to train and test the neural networks. The second data set, covering 52 wk of egg production, was used to validate the models. The mean absolute deviation, mean square error, and R(2) were used to evaluate the fit of the models. The MLP neural network had the best fit in the test and validation phases. The advantage of using neural networks is that they can be fitted to any kind of data set and do not require model assumptions such as those required in the nonlinear methodology. The results confirm that MLP neural networks can be used as an alternative tool to fit to egg production. The benefits of the MLP are the great flexibility and their lack of a priori assumptions when estimating a noisy nonlinear model.

A biolistic process for in vitro gene transfer into chicken embryos

Chicken embryos kept in culture medium were bombarded using a high helium gas pressure biolistic device. To optimize the factors that affect transformation efficiency, the lacZ gene under control of the human cytomegalovirus immediate early enhancer/promoter was used as a reporter gene. There was an inverse relationship between survival rate and transformation efficiency. The best conditions obtained for high embryo survival and high transformation efficiency were achieved with 800 psi helium gas pressure, 500 mmHg vacuum, gold particles, an 8 cm DNA-coated microparticle flying distance to the embryo and embryo placement 0.5 cm from the center of the particle dispersion cone. Under these conditions, transformation efficiency was 100 percent, survival rate 25 percent and the number of expression units in the embryo body cells ranged from 100 to 1,000. Expression of green fluorescent protein was also detected in embryos bombarded under optimal conditions. Based on the results obtained, the biolistic process can be considered an efficient method for the transformation of chicken embryos and therefore can be used as a model system to study transient gene expression and tissue-specific promoters

A biolistic process for in vitro gene transfer into chicken embryos.

Chicken embryos kept in culture medium were bombarded using a high helium gas pressure biolistic device. To optimize the factors that affect transformation efficiency, the lacZ gene under control of the human cytomegalovirus immediate early enhancer/promoter was used as a reporter gene. There was an inverse relationship between survival rate and transformation efficiency. The best conditions obtained for high embryo survival and high transformation efficiency were achieved with 800 psi helium gas pressure, 500 mmHg vacuum, gold particles, an 8 cm DNA-coated microparticle flying distance to the embryo and embryo placement 0.5 cm from the center of the particle dispersion cone. Under these conditions, transformation efficiency was 100%, survival rate 25% and the number of expression units in the embryo body cells ranged from 100 to 1,000. Expression of green fluorescent protein was also detected in embryos bombarded under optimal conditions. Based on the results obtained, the biolistic process can be considered an efficient method for the transformation of chicken embryos and therefore can be used as a model system to study transient gene expression and tissue-specific promoters.

Liberaçäo de espermatozóides das glândulas de armazenamento em poedeiras semi-pesadas / Sequence of sperm release from host glands in hens

Utilizaram-se, em dois experimentos, 224 galinhas e 30 galos brancos (SS) e 30 galos vermelhos (MM) de linhagens para ovos castanhos. No experimento I efetuaram-se duas inseminaçöes artificiais, com intervalo de 4 h, utilizando-se, na sequência, galos SS e MM. Os tratamentos definidos pela relaçäo de sêmen em ml, foram: T11 (0,05/0,05); T12 (0,02/0,05); T13 (0,05/0,02) e T14 (0,02/0,02). No experimento II realizaram-se duas inseminaçöes por semana, com alternância de galos, iniciando-se com SS, e reforços após 48 h (MM). Os tratamentos foram: T21 (0,05/0,05); T22 (0,03/0,05); T23 (0,05/0,03) e T24 (0,03/0,03). Realizaram-se quatro incubaçöes com quatro dias de coleta, para determinaçäo da fertilidade e porcentagem de pintos vermelhos (PPV). No experimento I, a utilizaçäo de 0,02 ml de sêmen resultou em baixa fertilidade (79,61 por cento). A PPV foi maior em T12 que T13 e T14, näo diferindo de T11. O maior volume de sêmen de machos vermelhos foi responsável pela maior PPV. Näo houve diferença significativa para fertilidade no experimento II. O fenótipo da maior parte dos pintos nascidos coincidiu com o fenótipo do galo utilizado na última inseminaçäo. Concluiu-se que a liberaçäo de expermatozóide obedece uma sequência, onde os espermatozóides da última inseminaçäo säo liberados com maior intensidade, dependendo, porém, do volume do sêmen