The effects of different Temperature Humidity Index (THI) values in cold, hot and El Niño (EN) climates on superovulation and embryo production were analysed on Holstein Friesian donor cows. There were significant differences in the THI among the three climates. The average temperature in the EN period was 6 degrees C higher than in the summer period of the previous 30 years. The number of corpora lutea (CL) and embryos were log- and back-transformed, Kolmogorov-Smirnoff test was used for normality and Lilliefors test was applied for significance. In the cold season THI was 70.74 +/- 1.35 and the average number of CL was 9.84 +/- 4.37. In the hot season the THI was 73.99 +/- 0.72 and the average number of CL was 9.70 +/- 4.49. When the THI, in the EN period, increased up to 79.74 +/- 4.01, the superovulation response was significantly (P < 0.01) reduced (average number of CL = 5.22 +/- 2.53). The embryo production result showed a similar tendency. In the hot period the average number of embryos obtained was 5.87 +/- 2.98. However, in the EN period it decreased to 4.21 +/- 2.05. Higher temperature reduced embryo quality. The proportion of live embryos (%) was 59.2 +/- 37.4 in the cold and 38.2 +/- 38.5 in the EN periods of the year (P < 0.01). However, ovarian sensitiveness showed adaptation to summer environment while the heat stress, which was more severe in the EN period, negatively affected the superovulation response and embryo production.