converting website visitors

ThePoultrySite.com - news, features, articles and disease information for the poultry industry

Featured Articles

European Conference Offered a Flavour of Global Research in Genetics and Breeding

23 February 2011

Invited speakers from across the world offered a glimpse into the rapid progress being made on poultry genetics, as well as on topics of more practical interest such as broiler breeding and incubation techniques at last year's European Poultry Congress. Jackie Linden, senior editor of ThePoultrysite, selects some of the highlights.


Recent Outcomes and Future Prospects for Avian Genomics

In his plenary paper, Alain Vignal from INRA at Castanet Tolosan in France explained that genomics was first defined as the association of molecular and cell biology with classical genetics, fostered by computational science. It started with the mapping and sequencing of genes on a global scale (genome) and now concerns the study of all genes, their products (transciptome, proteome) and interactions (interactome) in an individual cell or tissue under different conditions. For any species under investigation, the whole genome sequence in considered a peak in genomics research and although it is only one aspect, it gets most media attention.


The chicken genome was sequenced and published in 2004 but the new parallel sequencing technologies allows a great increase in sequence production and, as a consequence, more avian species' sequences, such as turkey and duck, are expected soon. Following the trend set by human genomics, the most recent chicken genomics studies include whole genome re-sequencing approaches. Nucleotide polymorphism can have an important impact on the implementation of marker-assisted or genomic selection for poultry, said Dr Vignal.

In-depth analyses of transcriptome, proteome and interactome (gene networks) data will allow increases levels of genome annotation, including that of non-coding RNA genes and regulatory regions, leading to refined global comprehension of the biology of avian species, he concluded.

Gene Networks to Study Complex Traits

Mari Smits of Wageningen Livestock Research in the Netherlands devloped the theme of gene networks and what their study can reveal.

Animal sciences have arrived at the threshold of a genomics data explosion due to the recent advances in high-throughput biological technologies such as massive parallel sequencing, transcriptome and proteome analysis, said Dr Smits. Biological processes are too complex to be explained by the analysis of individual components alone but the application of systems biology offers great promise for a global understanding of the expressions, interactions, modifications and regulation of cellular networks. One type of cellular network is the gene regulatory network, which can be viewed as an input-output device; the inputs are signals, signalling pathways, transcriptional factors etc., and the outputs are gene expression levels, the amount of mRNA produced by genes and the functional properties that arise from the network.

Dr Smits showed the inference of gene regulatory networks using seven-time series gene expression measurements derived from control and Salmonella-infected chickens. This work revealed so-called 'hub genes', the central elements in the gene regulatory network, which are potential targets to modulate the biological processes involved in intestinal development of young chicks and their host response to Salmonella infection.

Epigenetics Helps Explain Diversity

Ten years after the end of the human genome project, many of the fundamental questions remain unanswered, said Dr Andras Paldi of ISERM in Evry, France. It is becoming clear that genome sequencing alone cannot explain the diversity of phenotypic forms in the living world. How organisms with an identical genotype have dramatically different phenotypes is covered by 'epigenetics', which is usually used to design heritable phenomena that cannot be explained by the transmission of DNA. The phenotypic diversity of differentiated cells in an organism and the maintenance of their phenotypes after division is a representative example of how epigenetic mechanisms contribute simultaneously to the phenotypic diversification of the cells and mitotic inheritance of the phenotypic state, providing both variation and the faithful transmission of phenotypes. A gene's functional state can be transmitted through meiosis as well, he said.

The known examples of epigenetic inheritance such as imprinting defects in mammals show that the genetically identical organisms display different, highly stable heritable phenotypes that do not follow Mendelian segregation. High stability of epigenetic inheritance is increasingly recognised as an important factor in the development of multicellular organisms. In addition, substantial evidence shows that environmental stimuli can, in some cases, influence the transmission of epigenetic traits, Dr Paldi concluded.

Studying Changes in the Chicken Transcriptome

Larry Cogburn of the University of Delaware in the US presented work carried out at his institute, the universities of Maryland and Georgia and INRA in Nouzilly, France. They used the Del-Mar 14K Chicken Integrated System cDNA microarrays to examine transcriptional profile of multiple tissues – liver abdominal fat, breast muscle, hypothalamus and pituitary gland – during juvenile development (one to 11 weeks of age) in two sets of divergently selected broiler chickens (fat, FL and lean LL lines; high, HG and low LG growth lines). Hundreds of 'functional' differently expressed (DE) genes were discovered with individual analysis of each tissue across age and between genotype contrast.

This meta-analysis has enabled identification of unique enriched gene sets that are tissue-, genotype- and age-specific as well as common gene sets across these functional classes, said Dr Cogburn. He added that this knowledge can be used to assemble the building blocks of biological processes across multiple physiological systems that constitute the whole organism.

Maintaining Genetic Diversity

Global awareness has increased efforts to conserve animal genetic resources, explained Dr Harvey Blackburn of the National Center for Genetic Resources Preservation, part of the USDA Agricultural Research Service. Ex-situ conservation and management of these genetic resources is can now be achieved by an array of reproductive and genetic biotechnologies, he said.

By combining the biotechnologies, highly effective conservation actions can be achieved, without the need to maintain the animals alive. Dr Cogburn explained that this can ease the pressure on the research community to reduce the number of in-situ populations maintained. As th techniques are improved further, poultry populations can be securely cryopreserved and regenerated as needed by industry or the research community.

Managing Broiler Breeders with Lighting Regimens

The response of broiler breeders to light is strongly modulated by two factor irrelevant to the lighting of egg-type hybrids, namely, controlled feeding and photorefractoriness, explained Dr Rob Gous of South Africa's University of KwaZulu-Natal n his paper on managing reproductive performance of breeders. Where broiler breeders are reared on short days, the photorefractory influence is not evident. However, it becomes pertinent when photoperiods of 14 hours or longer are used, for example, in open-sided rearing houses in summer.

Dr Gous said that juvenile photorefractoriness can cause delays of three weeks or more in achieving sexual maturity. This leads to a larger initial egg size but fewer eggs per hen and so it has implications on feeding during the transitional period, i.e. from 20 weeks of age to onset of lay. In open rearing houses, natural daylength during rearing (latitude 30° South) proved to be more beneficial than a constant 14-hour programme.

A model for predicting the effect on age at sexual maturity of 20-week body weight and the photoperiod used during rearing has been developed from the results of a number of trials conducted by Dr Gous. He continued that egg production is inferior when the breeders are exposed to 16-hour days because the advance in the onset of adult photorefractoriness, i.e. the end of the breeding season, is proportional to the stimulatoriness of the photoperiod provided inlay.

Superior egg production is achieved when broiler breeders are reared on eight hours and subjected to a 13-hour photoperiod in lay, explained Dr Gous. There is no advantage in providing photoperiods longer than this, nor is there any advantage is using a light intensity greater than 70 lux, he added.

Thermal Manipulation During Incubation Affects Broiler Performance

Shlomo Yahav of Israel's Volcani Center explained how epigenetic adaptation is involved in the response to thermal manipulations during incubation aimed at improving the bird's thermotolerance and improving carcass quality.

The incubation period of broilers has received more attention during the last decade, he said, because it has been shown that environmental manipulation may induce long-lasting physiological memory (LLPM) caused by epigenetic adaptation. Dr Yahav reviewed the effects of long-term mild manipulations.

He described how temperature during the period of hypothalamus-pituitary-thyroid and adrenal axes development and maturation leads to a significant improvement of thermotolerance in broilers up to marketing age. This is explained by both a significant reduction in heat production and with a significant increase in sensible heat loss as well as reduced signs of heat stress. The responses were detected already during embryogenesis. Dt Yahav added that the thermal manipualtion also increased relative breast muscle weight and reduced the abdominal fat pad.

References

Blackburn H. 2010. Reproductive technologies and management of genetic diversity.
Cogburn L. et al. 2010. Meta-analysis of the chicken transcriptome across multiple tissues, genotypes and ages during juvenile development.
Gous R. 2010. Managing reproductive performance in broiler breeders with lighting regimens.
Paldi A. 2010. Genetics and epigenetics.
Smits, M. et al. 2010. Gene networks as a tool for the study of complex traits.
Vignal, A. 2010. Recent outcomes and future prospects arising from avian genomics.
Piestan Y. et al. 2010. Thermal manipulations during broiler's embryogenesis – its effects on thermotolerance acquisition and chicken's quality. (presented by S. Yahav).
All papers were presented at the 13th European Poultry Congress in Tours, France in August 2010. Hosted by the French branch of WPSA.

February 2011



Related Articles

Most Read Articles


Our Sponsors

Partners


Seasonal Picks

Poultry Breeds and Management