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Holstein-Friesian dams (n = 28) and daughters (n = 28) were superovulated (total number of observations was 235) to determine the repeatability and heritability of ovulation number and embryo collection result for FSH treatment. The donor cows were superovulated with FSHp, artificial insemination was performed and embryo collection was carried out 7 days later. For the analysis, the raw corpdata of the number of corpora lutea (CL), the number of collected embryos (EM) and their log-transformed values were used (log CL, log EM). The genetic parameters were calculated by using the VCE4 software. For calculating heritability, the number of embryo collection was used as a random effect; for calculating repeatability, the permanent environment was fitted. The additive genetic variance of CL was 8.91 and that of the EM was 9.23. The additive genetic variance for the log CL and log EM were 0.457 and 0.340, respectively. The estimated heritability for CL and EM were 0.234 and 0.159, and repeatability were 0.386 and 0.301, respectively. Higher heritabilities but lower as the previous repeatabilities were observed for the log-transformed data, 0.266, 0.194 and 0.294, 0.208 for log CL and for log EM, respectively.

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 °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, KolmogorovSmirnoff 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.Key words: Heat stress, El Niño phenomenon, donor cows, superovulation, embryo production Cattle, like other mammalian species, are homoiothermic animals that regulate internal temperature within a narrow range (~38.0 to 39.3 °C). An animal maintains homoiothermy by matching the amount of heat produced through metabolism with the heat flow from the animal to the surrounding environment. Heat flow occurs through a process dependent on the surrounding temperature

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