Thermotolerance in Broiler Chickens: Evaluating the Influence of Embryonic Thermal Manipulation and <em>in-ovo</em> Feeding of Lysine and Cysteine in a Hot Tropical Environment

Purpose: The physiological mechanism of action of low or high combinations of lysine and cysteine in-ovo feeding combinations needs to be elucidated. This study aimed to determine the influence of high or low combinations of lysine and cysteine on the growth, thermotolerance, haematochemical, and antioxidant parameters of heat-stressed broiler embryos.Research Method: A total of 2000 broiler hatching eggs were exposed to a relative humidity of 55% and temperature of 39.0ºC for 6 hours daily from day 10 until day 18. On day 18, 1500 eggs having living embryos were taken at random into 6 treatments containing 250 eggs per treatment with 5 replicates of 50 eggs viz: eggs without in-ovo injection (UIJ), eggs treated with in-ovo injection of 0.5mL distilled water (DWT), 2mg lysine (LYS), 3.4mg cysteine (CYS), 3.4mg cysteine+2mg lysine (CLHD) or 1.7mg cysteine+1mg lysine (CLLD).Findings: The blood total protein of CLLD birds was higher (P<0.05) compared to the others at the starter phase. The ALT of CLHD and CLLD birds were lower (P<0.05) than other treatments at the finisher phase. The malondialdehyde of DWT and UIJ broilers was higher than the other treatments at the starter and finisher phases.Research Limitation: This study was carried out in a hot season. More studies are needed under different seasons of the year using in-ovo amino acids.Originality/Value: It can be concluded that in-ovo injection of lysine-cysteine positively altered the growth rate, and biochemical and antioxidant indices of broilers. The low combination of the amino acids had a more sustained effect at the market age.