Mechanisms of adaptation to heat stress and a suboptimal diet in laying hens – ChickStress

Climate change, economic constraints and social concern for a sustainable agriculture will strongly influence animal production systems. Poultry production is a major source of proteins for human food all over the world. Improving the adaptation of chicken lines to variable conditions of climate and feed is a requirement to meet the challenge of a growing human population by 2050, particularly in Asian and African countries with a hot climate. Whereas heat tolerance in chickens has been studied for many years, a global understanding of the genetic control of adaptation is still absent and targeted selection criteria are also lacking. Variation in feed consumption is known to influence heat tolerance in chickens and genetic variation in feed intake must be taken into account in order to analyse mechanisms of heat tolerance. Furthermore, feed quality is likely to fluctuate, especially because of economic constraints. Thus, the possible connection between mechanisms of heat adaptation and mechanisms of adaptation to feed change needs to be thoroughly investigated.

We propose to use up-to-date genomic methods to study mechanisms of adaptation to heat (heat waves in particular) or to feed change (use of co-products of grains and oilseeds for example) of a range of contrasted genotypes, in order to cover a wide range of genetic and epigenetic variation, within and between populations. The laying hen is targeted because it has a long production cycle and is particularly exposed to the risk of seasonal heat waves. The project takes advantage of the availability of different lines or breeds maintained at INRA in order to provide a body of fundamental knowledge on adaptive mechanisms regarding heat tolerance and adaptation to feed change in a domestic bird. Four experimental lines will be studied: brown egg layers selected for a low residual feed intake (R-) or a high residual feed intake (R+); a line of Fayoumi chickens, from the Egyptian Fayoumi breed known to be heat tolerant and disease resistant; a line of brown-egg layers carrying the "naked neck" and "dwarfism" genes which decrease the effects of heat on performance. These lines are moderately inbred and exhibit strong variation between them. A commercial line from Novogen (partner of the project) will be studied in connection with an on-going project on genomic selection (ANR UtOpIGe) where sires are genotyped and tested. Sire families differing in adaptation to a feed change will be produced to be tested for heat tolerance.

The work program is organised in 6 tasks: coordination; challenging and phenotyping; transcriptomics; epigenetics; data integration; dissemination. All genotypes will be challenged with a heat stress at the time of high egg production, just after the peak of lay. The R- and R+ lines and Novogen line only will be tested independently on the sub-optimal diet already used to challenge the commercial line. A control, unstressed, group will be maintained for each genotype. Hypothalamus, liver and leukocytes (at 2 time points) will be collected for DNA and RNA extraction. Performance records and physiological indicators will be combined with transcriptomic and DNA methylation studies in order to identify regulatory pathways of adaptation. Heritability of methylation pattern of a subset of loci will be estimated in the commercial line. Analyses will benefit from data produced by two related, already funded projects that will provide genetic data (marker genotypes and genetic values for Novogen and resequencing of the whole genome for R-R+).

These data obtained in a wide range of domains (genomics selection, functional genomics, physiology and production) in contrasted genotypes will give us a unique opportunity to build an integrative scheme for adaptation mechanisms and regulation, in chicken.