64 Is the proteome of the oviductal fluid in dairy cows affected by heat stress?

Heat stress is one of the best-known manifestations of global warming in livestock, resulting in lower dry matter intake, milk yield, and fertility. Fertility problems associated with heat stress are mainly caused by the effect of increased body temperature on oocyte and embryonic development. In addition to the direct effect of heat stress, the early embryonic development might be affected by elevated temperature due to alterations of the maternal reproductive tract. The elevated metabolism of high-yielding dairy cows may further contribute to dysregulation of homeothermy in the oviduct. The aim of the study was to investigate the effect of short-term heat stress under Lower Austrian conditions on the maternal microenvironment in the bovine oviduct in cows with high or low milk yield. A total of 15 Simmental cows were divided into two groups according to their milk yield during Days 40 to 50 postpartum: low-yielding cows (296.66 l ± 35.65) and high-yielding cows (386.30 l ± 33.70). The oviducal fluid was collected both during the wintertime (temperature-humidity index (THI) < 72) and summertime (the animals were exposed to a THI ≥ 72 from the start of the synchronization to the collection of oviducal fluid). Only animals in a luteal phase were synchronised using PGF_2α and gonadotrophin-releasing hormone 48 h apart to induce ovulation. The oviducal fluid was collected by transvaginal endoscopy 48 h later: 0.5 mL of phosphate-buffered saline was flushed back and forth three times in the oviduct ipsilateral to the fresh corpus luteum (D1), the recovered fluid was centrifuged and prepared for further analysis. Three to four samples per group were digested with trypsin/lysC and injected in a nano-liquid chromatography (nLC) tandem mass spectrometry (MS/MS) system (Orbitrap Q Exactive Plus, ThermoFisher). Generated data were label-free quantified with the MaxQuant software (v2.2.0.0) and statistical analysis was performed in R (https://www.R-project.org/). In total, 2368 proteins were identified in all recovered oviducal fluids. The oviducal proteome of low-yielding cows differed significantly from that of high-yielding cows in summer and winter. The oviducal proteome of low-yielding cows differed between seasons, in contrast to that of high-yielding cows that showed negligible differences between both periods. In conclusion, it was shown that in addition to the metabolic load of high-yielding animals, the effect of heat stress on the proteome of the oviducal fluid is weak. Thus, the influence of elevated temperature was visible only in low-yielding cows with less metabolic activity. Further detailed analysis of proteome profiles is planned to better define the effect of elevated temperature on the composition of the oviducal fluid.

This study was funded by the Gesellschaft für Forschungsförderung NÖ, FTI-Call 2020 (FTI20–012).