Egg physical characteristics and hatchability

The physical characteristics of the egg play an important role in the processes of embryo development and successful hatching. The most influential egg parameters are: weight, shell thickness and porosity, shape index, described as maximum breadth to length ratio, and the consistency of the contents. The average values of the physical characteristics mostly meet the requirements for the embryo's development. For those eggs, whose parameters do not fall in to the average range, the incubation process is more successful if the shell is thicker than average, the eggs are more pointed rather than round, and the contents firm. The results reported for investigations into incubating eggs, whose weights are not within the average values, are contradictory. Both thick shells and firm interiors, which are accepted as being higher than average, lead to an increase in egg weight, which probably results in the more successful hatching of embryos from heavier eggs

Current strategies for the assessment and evaluation of genetic diversity in chicken resources

Chicken genetic resources comprise a wide range of breeds and populations including red jungle fowl (the assumed progenitor of all domestic breeds), native and fancy breeds, middle level food producers, industrial stocks and specialised lines. Based on the suggestion that the more distant a breed or population is the more likely it is to carry unique genetic features, the assessment of genetic distances by means of molecular marker information may provide useful information for initial evaluation of chicken genetic resources. During the last two decades several molecular marker classes have become available. Variable numbers of tandem repeat loci, in particular microsatellites, have been successfully used in chicken diversity studies. Genetic diversity measures using the highly polymorphic variable number of tandem repeat lociyield reliable and accurate information for the study of genetic relationships between chicken populations. First results of the European project on chicken biodiversity (AVIANDIV) obtained from microsatellite typing in DNA pools of 51 diverse chicken breeds showed that jungle fowl populations, traditional unselected breeds and broiler lines appear to be widely heterogeneous populations that may include a large portion of the genetic diversity of the tested breeds. In contrast, highly selected strains (layers and experimental lines) are characterised by a lower polymorphism. They behave as outliers from the set of breeds sampled. Single nucleotide polymorphism is a new and very promising molecular marker system which offers opportunities to assess the genetic diversity in farm animal species differently by investigating the mode and extent of changes in certain positions in the genome