Overall cleavage rates were 72% and 56% for Nellore and Angus embryos, respectively. In both breeds, heat stress at 41 C decreased (P < 0.05) the percentage of 16-cell embryos that became blastocysts when compared with embryos cultured at 38.5 C (Table 3). Logistic regression analysis detected a tendency (P ¼ 0.1) for heat stress to
decrease pregnancy rates at Days 30 to 35 for Angus embryos. There was no significant interaction between
breed and temperature in the percent of blastocyst or pregnancy rate. When pregnancy rates were compared
using contrasts, recipients that received heat-stressed Angus embryos had lower pregnancy rates (P ¼ 0.08)
than all other groups.