In a recent unpublished experiment, embryos from Angus or Nelore cows produced using oocytes
obtained by oocyte pickup (OPU) procedures were exposed to a culture temperature of 41 ◦C for 12 h
beginning 96 h after fertilization. Thereafter, embryoswere transferred at the blastocyst stage to crossbred
recipient heifers. The pregnancy rates after transfer were: 29.4% (15/51) for non-stressed Nelore
embryos, 29.0% (11/38) for stressed Nelore embryos, 21.4% (6/28) for non-stressed Angus embryos
and 7.1% (1/14) for stressed Angus embryos. In both the present study and those obtained previously
(Barros et al., 2002) data clearly indicate that Nelore embryos are better able to survive heat shock at
early stages of development and more capable of originating pregnancies following heat shock than
B. t. taurus embryos.