Ashour, GEl-Sayed, AshrafKhalifa, MGhanem, Nasser2021-01-302021-01-30441902322456810.29252/scil.2020.wvj79http://repository.msa.edu.eg/xmlui/handle/123456789/4409The deleterious effect of heat stress on cumulus-oocytes complexes (COCs) competence is well recognized in different livestock species. Therefore, the present study aimed to investigate the effect of physiologically relevant heat stress on the developmental competence of camel COCs during in vitro maturation (IVM). A total of 1548 COCs were divided into six groups in this study. The groups were named K1 and K2 representing good and low-quality COCs incubated at 38.5oC for 30 hours. While K3 and k4 represent good and low-quality COCs exposed to 41oC for the first 6 hours of IVM. Finally, K5 and k6 represent the groups of good and low-quality COCs exposed to 42oC for the first 6 hours of IVM. After exposure of COCs to heat stress at 41°C and 42°C during the first 6 hours of in vitro maturation, the COCs were incubated at 38.5°C for 24 hours of IVM. The in vitro matured COCs were activated to cleave using ethanol followed by 4 mM 6-DMAP and developed embryos were cultured in vitro for 7 days post parthenogenetic activation. The results of this study indicated that heat stress at 42oC significantly decreased the Pb (polar body) extrusion rate in K4 and K6, compared to other groups. Additionally, the embryo cleavage rate was significantly lower for good and low-quality oocytes exposed to heat stress (K2, K3, K4, K5, and K6), compared to good quality COCs of the control group (K1). The cleavage rate was lower for low quality (K2; 63 ± 1.28) than good quality COCs (K1; 53 ± 1.85). The percentages of oocytes that developed to the blastocyst stage were lower for K2, K3, K4, K5, and K6 than K1. Moreover, the blastocyst rate was lower for K2 (9 ± 0.22) than K1 (15 ± 0.22). The results of this study indicated that exposure of camel oocytes to heat stress for 6 hours during in vitro maturation severely reduced extrusion of polar body, cleavage, and blastocyst rates. The low-quality camel COCs were reduced developmental capacity than good quality oocytes. © 2020, World''s Veterinary Journal. All Rights Reserveden-USCamelEmbryo developmentHeat stressOocyteArticlehttps://dx.doi.org/10.29252/scil.2020.wv79