Mimicking the temperature gradient between the sow's oviduct and uterus improves in-vitro embryo culture output

This work was designed to determine temperature conditions within the reproductive tract of the female pig and study their impact on assisted reproductive technologies. Temperatures were recorded using a laparo-endoscopic single-site surgery assisted approach and a miniaturised probe. Sows and gilts were used to address natural cycle and ovarian stimulation treatments, respectively. According to in-vivo values, invitro fertilisation was performed at three temperature conditions (37.0 °C, 38.5 °C and 39.5 °C) and presumptive zygotes were cultured in these conditions for 20 hours while further embryo culture (21-168 hours post-insemination) was maintained at 38.5 °C. After 20 hours, different fertility parameters were assessed. During embryo culture, cleavage and blastocyst stages were evaluated. Sperm membrane fluidity at the experimental temperatures was studied by using differential scanning calorimetry and fluorescence recovery after photobleaching techniques. An increasing temperature gradient of 1.5 °C was found between the oviduct and uterus of sows (p < 0.05) and when this gradient was transferred to pig in-vitro culture, the number of poly-nuclear zygotes after in-vitro fertilisation was reduced and the percentage of blastocysts was increased. Moreover, the temperature transition phase for the boar sperm membrane (37.0 °C) coincided with the temperature registered in the sow oviduct, and sperm membranes were more fluid at 37.0 °C compared with that of sperm incubated at higher temperatures (38.5 and 39.5 °C). These data suggest that there may be an impact of physiological temperature gradients on human embryo development.