The Epigenetic Approach of Broiler Chickens to Cope with Global Warming

Poultry products are one of the most important sources for protein and other ingredients of human diet.

Scientists expect that the average global surface temperature will rise by 0.6-2.5°C until 2050. Global warming enhances desertification which on a yearly basis enlarges the arid to semi arid lands. Soil degradation caused by human intensive agriculture induces desertification too. More than 110 countries consist of dry/degraded lands that are potentially at a desertification risk. Dry land compromises 41.3% of the global terrestrial land, which is the home for 34.7% of the global population, expected to be raised by 2050 to 9 billion. These evidence led the UN General Secretary to announce that “The world farm production must be raised by 50% by 2030 to meet human demands for food”. Thus, the poultry industry faces great challenges: a. increasing production performance and quality; b. improving poultry thermotolerance.

Birds are endotherms, able to maintain their body temperature within a narrow range. However, an alteration in body temperature as a result of exposure to extreme environmental conditions may lead to a cascade of irreversible thermoregulatory events that could be lethal for the bird. To sustain thermal tolerance and avoid the deleterious consequences of thermal stresses, three direct responses are elicited: the rapid thermal stress response; acclimation; and epigenetic temperature adaptation. Although domestic fowl respond to changes in the environment with the same mechanisms as other endotherms, their intensive production causes them to face serious difficulties in coping with extreme environmental changes. Recent decades have seen significant progress in the genetic selection, on the one hand, of fast-growing meat-type broiler chickens and turkeys and, on the other hand, of egg-producing laying hens. However, the significant improvements in body and muscle growth and in egg production have not necessarily been accompanied by equivalent growth of specific visceral organs, and the probable consequence is a reduced ability to cope with extreme changes in environmental temperatures.

The incubation period of broiler chickens gets more attention during the last decade. It can be related to the recognition that during this period various environmental manipulations may induce long-lasting-physiological-memory (LLPM) caused by epigenetic adaptation. Several environmental manipulations have been adopted lately; this abstract focuses on thermal manipulations (TM's) based on the strategy of long term mild manipulations. The hypotheses underlying this strategy are: a. during embryogenesis, it is possible to induce LLPM; b. LLPM can be defined, most probably, as an alteration in the threshold response to changes in the environment; and c. the manipulations must be conducted during sensitive embryogenesis periods, by means of a specific level and duration. These manipulations will induce an improved potential to withstand changes in the environment during the bird's life span. Heat TM's (elevating incubation temperature from 37.8 to 39.5°C coupled with relative humidity elevation from 56 to 65% for 12 hours, or continuously, on each day from day 7 to 16 of incubation) during the period of the hypothalamus-pituitary-thyroid (thermoregulation) or adrenal (stress) axes development and maturation were employed in these experiments. These treatments demonstrated a significant improvement of thermotolerance acquisition in broiler chickens up to marketing age. The improvement achieved by a significant reduction of heat production, coincided with significant increase in sensible heat loss and significant decline in stress level. These responses were detected already during embryogenesis, where oxygen consumption, heart rate, eggshell temperature, as well as plasma thyroid hormones (thyroxin - T4 and triiodothyronine - T3) and corticosterone concentrations were significantly lower in the TM's embryos after the exposure to TM's. It also appeared to improve the quality of broilers that were treated for 12 hours during incubation, by means of improving feed conversion rate, increasing breast muscle relative weight and reducing abdominal fat pad. It is concluded that TM's during embryogenesis improve thermotolerance during life span coupled with improving quality of the 12 hours-treated broilers.