Keyword: epigenetics, thermal stress, animal welfare, posture. Published Date: 4/1/2020 Page.134-148 Vol 8 No 04 2020 Abstract The objective of the experiment was to evaluate the influence of thermal manipulation on the improvement of hatching eggs of different weights of laying breeder hens in the last embryonic stage. The experiment was carried out in a commercial hatchery of laying breeder hens, located in Birigui - SP, Brazil. 1950 light-colored eggs of the Dekalb White commercial strain were used. The eggs were classified among different sizes and n in hatching trays. In the period from 19 to 21 days, two hatching machines were used, where the first machine maintained the temperature and humidity values of the hatchery's standard air (37.0 ° C and 60% RH) and in the second machine the temperature was adjusted to 37.7 ° C with 60% RH. The treatments differed according to the residence time in the second machine, and egg weight (G and M) controls T1 (0h-G) and T6(0h-M), 1 hour T2(1h-G) and T7(1h-M), 3 hours T3(3h-G) and T8(3h-M), 6 hours T4(6h-G) and T9(6h-M) 9 hours T5(9h-G) and T10 (9h-M). The design was completely randomized, in a 2X5 factorial scheme. Regarding thermal stimulation, the best results were observed in the 1h-G treatment. However, in the productive life of these birds, the thermal stimulation showed no influence. Concluded that for large eggs (G), the residence time of 1 hour (T2), obtained a better index of commercially viable females and lower rates of late-stage embryo mortality and shelter. IMPROVEMENT PERFORMANCE OF HATCHERY DUE TO THERMAL EGGS HANDLING Jorge Ikefuti Filho;Érik Harada dos Santos;Leda Gobbo de Freitas Bueno;Douglas D’Alessandro Salgado;Danilo Florentino Pereira;Mario Mollo Neto;Silvia Regina Lucas de Souza International Journal for Innovation Education and Research ISSN: 2411-2933 DOI: https://doi.org/10.31686/ijier.vol8.iss4.2272