Effect of Heat Stress on Bovine Embryonic Development

Abstract

To determine the effect of heat stress initiating at the 4-8 cells stage on bovine embryo to blastocyst stage and sire effect on embryonic development under heat stress conditions. Frozen semen from four Charolais sires were used to produce bovine embryos. Four to eight cells stage embryos that were produced from oocytes collected from slaughterhouse ovaries were submitted to two heat stress treatments. Experimental design in this study was the randomized complete design (CRD) with 7 replications per sire. The experiments were conducted at the Faculty of Veterinary Medicine, Khon Kaen University. At
day 3 after fertilization, 4-8 cells stage embryos were selected and divided into 3 groups; group1: culture at 38.5 O C (control), group 2: culture at 41°
C for 8 h once (heat 8h), and group3: culture at 41° C for 8 h every day until day 7 after fertilization (heat 8h/d). Embryos developed to the blastocyst stage were recorded at day 8 after fertilization and were determined for the
number of cells by differential staining technique. The results of this study were showed that daily exposure to heat stress (heat 8h/d) reduced development of 4-8 cell stage embryos to blastocyst stage compared with control (P<0.05). When the% of blastocyst development from heat stress groups were normalized to control (control = 100%) the total blastocyst development in heat 8h/d group from sire 3 (62.9%)  was lower than that of control group (P<0.05). However, the% of expanded blastocyst development in heat 8h/d group were
also significantly reduced (P<0.05) in all sires.The numbers total cell and trophectoderm of blastocysts in heat 8h/d group were lower than those of heat 8h and control groups(P<0.05).The numbers of inner cell mass among groups were not different. In conclusion, this study was suggested that there was no distinct effect of sires, within the same breed, on development to blastocyst stage under heat stress condition. Heat stress reduced the number of total cell in blastocyst stage through the reduction in the number of trophectoderm.