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THERMOCHICK: What are the mechanisms involved in embryo heat acclimation?

© Inra
Broiler chickens present poor resistance to climatic variations, including heat waves, which have a negative impact on welfare and growth of animals. While the chicken production grows in hot countries and in the context of global warming, one strategy is to acclimate the chickens to heat during egg incubation.

The project THERMOCHICK is a basic research project coordinated by A. Collin, involving other young researchers from the Poultry Research Unit of INRA, S. Métayer-Coustard, S. Mignon-Grasteau, C. Praud, C. Berri and C. Hennequet-Antier. It also received the scientific support from M.J. Duclos and S. Tesseraud and the collaboration of the Israeli researcher S. Yahav. The project began in September 2009 and lasted 51 months. It was funded by ANR (French Agence Nationale de la Recherche).
Broiler chickens present poor resistance to climatic variations, including heat waves, which have a negative impact on welfare and growth of animals. While the chicken production grows in hot countries and in the context of global warming, one strategy is to acclimate the chickens to heat during egg incubation. The project THERMOCHICK aims to understand the mechanisms involved in this early conditioning and explore its effects on heat tolerance, stress, growth and quality of chicken meat.

The objectives are both scientific and applied:

  1. Determine which metabolic pathways are altered when the animal was heat-conditioned, and how these pathways are regulated in vitro,
  2. Examine the associated effects on growth, oxidative stress and quality of chicken meat. This project also allows us to propose new characters potentially interesting for selection of heat tolerant chickens.

Embryo heat conditioning is a promising approach to reduce heat stress in livestock and increase the sustainability of poultry production. Physiology, molecular biology and genomics help to elucidate the mechanisms of embryo heat acclimation
At the Poultry Research Unit of INRA, we studied the consequences of egg incubation conditions including cyclic high temperature (39.5°C and 65% relative humidity, 12 h/d from d7 to 16 of incubation vs. 37.8°C and 56% RH for the controls) on growth performance and the quality of chicken meat. Our results suggest that stress during a heat challenge at slaughter age is limited in heat-conditioned compared to control chickens. Using a thermocycler acquired during the project we studied the expression in the muscle of target genes important for energy use by the bird and its heat production. The high throughput study of the expression of a large number of genes (transcriptome) highlights potentially new genes important for the adaptation of the animal to heat. Mitochondrial function regulating the use of energy and cellular aging (oxidative stress) was explored through fluorimetric methods in heat-conditioned or controls exposed to heat challenge. Finally, using muscle cell cultures, we explored the hormonal regulation of the metabolic pathways involved in embryo heat acclimation.

Major results of the project

TM chickens presented a lower body temperature and different physiological parameters compared to control chickens, and a lower level of stress during a subsequent heat challenge. They were lighter but less fat than controls, and meat quality was not impaired. Muscle expression of genes controlling heat production and loss was changed by the treatment. Six times more genes responding to heat challenge were found in TM than in controls chickens, some of which regulating long-term gene transcription. These studies, conducted in collaboration with an Israeli laboratory, lead to new projects related to oxidative stress and epigenetics in birds.