Submitted to: International Embryo Transfer Society Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: January 1, 2001
Publication Date: January 1, 2001
The objective of this study was to determine whether the deleterious effect of heat shock on embryonic development was less for embryos from heat- tolerant breeds (Brahman and Senepol) than for embryos from heat-sensitive breeds (Angus and Holstein). Estrous was synchronized in 20 Angus, 20 Brahman, 20 Holstein, and 11 Senepol cows that were slaughtered on d 2 post-estrus. For each replicate, oocytes were pooled from a pair of cows from each breed. Oocytes were fertilized with sperm from a bull of the same breed; a separate bull was used for each pair of cows. At day 4 after insemination, embryos were separated into two stages: 4 to 8 or =/> 9-cell stage. Embryos were exposed to either 38.5 C continuously or to 41 C for 6 h and 38.5 C thereafter. Ovulation rate following synchronization was similar among breeds as was the number of recovered oocytes/cow. Cleavage rate was higher for Brahman (87.0%) than for Senepol, Holstein, and Angus (76.0, 76.0, and 68.0%, respectively). The proportion of embryos develop- ing to the blastocyst stage at day 8 after insemination was influenced by a breed x stage x temperature interaction. For embryos =/> 9-cells, the decrease in development caused by 41 C for 6 h was less for Brahman (29.0% at 38.5 C vs 15.3% at 41 C) than for Holstein (32.0 vs 0.0%) and Angus (51.0 vs 2.6%). Development of Senepol embryos was 7.0% at 38.5 C vs 0.0% at 41 C. Overall, embryos at the 4 to 8 cell stage (which were retarded in development) were less able to develop to the blastocyst stage. In con- clusion, Brahman embryos are better able to develop following heat shock than are Angus and Holstein embryos. The large breed effects even at 38.5 C imply that either optimal IVF conditions differ among breeds or the status of the oocytes at the time of collection varied among breeds.