Monthly and lunar variation of pregnancy rates and gestation losses after transfer of in vitro produced bovine embryos in a southern tropical region of South America

This retrospective study investigated the effect of month and lunar cycle on pregnancy per embryo transfer (P/ET) and pregnancy losses following the transfer of in vitro-produced embryos (n = 11,434). Oocytes were collected by ovum pick-up from Gyr donor cows on farms in Minas Gerais, Brazil. In vitro Gyr × Holstein embryos were produced using standard commercial laboratory protocols. Only fresh day-7 blastocysts and expanded blastocysts were transferred into recipient cows, and pregnancy was confirmed by ultrasound at 30 and 60 days post-transfer. The lunar cycle was divided into 30 periods of 0.98 days each. Data were analyzed using logistic regression. The P/ET was significantly influenced by the month of transfer (IVP-ET) (P < 0.0001), with consistent patterns at both 30 and 60 days. Rates were lowest in January and February, increased through June, declined in July and August, and peaked during the last four months of the year. Pregnancy losses varied across months (P = 0.1888), with highest rates in July and lowest in June. The lunar cycle also affected P/ET (P < 0.01), with higher rates during the waning phase compared with the crescent phase at both 30 days and 60 days. Pregnancy losses fluctuated throughout the lunar cycle (P = 0.2744), ranging from 3.6 % to 15.6 %. Notable positive deviations in the mean frequency of pregnancy losses were observed around the full moon and new moon. In conclusion, P/ET was significantly associated with both the month and the lunar cycle, whereas pregnancy losses varied considerably across months and days of lunar cycle but did not reach statistical significance.