Recipients’ pregnancy rate was affected by season but not by the temperature humidity index (THI) in an equine commercial ET program in Southern Europe

This study retrospectively analysed the effects of different environmental factors such as the photoperiod, temperature/humidity index of 19 years of a commercial embryo transfer programme performed in central Italy. From 340 donors of different breeds and aged between 2 and 25 years, 576 embryos of an excellent or good quality were obtained by uterine flushing on days 7–8 after ovulation. The embryos were transferred to 259 recipients, aged between 2 and 16 years, and belonging to different breeds. Both the donors and the recipients were employed for several cycles/years. At the time of transfer, the recipients were in diestrus, from day 4 to day 8 after ovulation, and were classified as excellent or good based on clinical examination findings. Out of the total number of embryos transferred, 437 pregnancies were obtained at 14 days (75.9%), with 48/437 (10.1%) embryonic losses at 40 days; with no significant differences among years. Significant differences (p < .05) were observed between 14‐day pregnancy rates for transfers performed during the spring transition and breeding seasons (77.1%) compared to those performed during the autumn transitional season (57.9%). No effect of temperature/humidity index was found on pregnancy rates or pregnancy losses after the transfer to the recipients (p > .05). Embryo transfer during autumn was less successful than the transfers performed during the spring transition and the breeding season.