COMPARATIVE EVALUATION OF THE PECULIARITIES OF STRESS REACTIVITY OF THE RUSSIAN WHITE BREED CHICKEN WITH sw+ MUTATION AND AMROX IN HYPOTHERMIA CONDITIONS DURING EMBRYONAL AND EARLY POSTNATAL PERIODS OF ONTOGENESIS

Modern programs of conservation of poultry genetic resources suggest the need to study specific characteristics of breeds for their further use in breeding. The ability of chickens to adapt and maintain productivity over a wide range of temperatures is an important economically significant feature, since maintaining a temperature optimum to realize the genetic potential of productivity requires significant energy costs. Regarding this, the unique long-term experiment of RRIFAGB on the population of Russian white breed chickens, started by A.N. Sokolova, is of interest. This population was created through selection for resistance to low temperatures in the first days of life (1522 C in the first 5 days with a gradual decrease to 14-11 C to 21-30-day-old age) and the keeping of adult chickens in winter at a temperature below 0 C. As a result, genotypes appeared, differing not only in thermal resistance, but also possessing an increased resistance to diseases of the leukemia-sarcoma complex and white embryonic down (so-called «snow whites»). The aim of this work was to investigate the degree of adaptive response of Russian white embryos (Gallus gallus domesticus) and neonatal chicks, homozygous for the gene sw+, to a lower ambient temperature compared to the breed Amrox, resulting in the first demonstration of interbreed differences in epigenetic adaptation of chickens in early ontogeny. The thermal stability of sw+ homozygous Russian white chickens («snow white» population) and Amrox breeds in prenatal (12.5 days of incubation) and early neonatal periods (when removed from the incubator) was studied in a comparative aspect. Thermal stability in embryos (n = 70) was assessed by changes in the volume of extraembryonic fluid; in chickens (n = 60) — by changes in body temperature and characteristic behavioral reactions under hypothermia. Body surface temperature was determined using Thermal Expert FL 13mm f/1.0 thermal imaging camera, and rectal temperature was determined with an electric thermometer. Interbreeding differences in the response to low temperatures in embryos and 1-day-old chickens were revealed. Cooling of incubated eggs for 6 hours at +20 C caused a slight expected decrease in the embryo weight in both breeds, but led to an increase in the volume of allantois-amniotic fluid (as a protective mechanism). The decrease in temperature caused an increase in the amount of fluid in embryos of both breeds, but in «snow whites» by 8.2 % and in Amrox embryos to a lesser extent, by 6.7 %. It is found that neonatal «snow white» chicks, as a result of a 2-hour exposure at 16 C, lose body heat less intensively (the body temperature range of 32,4-17,0 C) than Amrox chickens (the body temperature range of 28,2-14,5 C) with no critical decrease in rectal temperature allowed. The rectal temperature of Amroxes reduced by 12.7 % or 5.1 C (p < 0.001) compared to that at the moment of removal from the incubator, while in «snow whites» — only by 3.7 % or 1.4 C. The «snow white» сhicks are mobile, whereas the Amrox сhicks are torpid. Thus, the chickens of the Russian white breed, homozygous for sw+ gene, along with the snow-white color of the down at 1-day age, have more perfect mechanisms of thermoregulation (mainly physical, not chemical) and are better adapted to the conditions of low temperatures during embryonic and early postnatal periods.