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Steele, Heather; Maalouf, Walid; Makri, Dimitra; Reese, Sven ORCID logoORCID: https://orcid.org/0000-0002-4605-9791 and Kölle, Sabine (15. January 2019): How does sperm sexing in the bovine affect functional morphology of early embryos?

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Sperm sexing is a technology which has been developed to increase the number of female calves in the dairy industry. However, the fertility of bulls after sexing may be reduced up to 25 %. Therefore, the aim of this project was to elucidate the causes for reduced fertility after sperm sexing. For this purpose, bovine oocytes were aspirated from ovaries from cows immediately after slaughter. Oocytes were matured in vitro, fertilized with sexed or conventional semen from the same bull and cultured for 8 days until the blastocyst stage. Embryonic development of embryos was then compared using time lapse video microscopy and fluorescence microscopy. Our results showed that embryos derived from sexed semen were significantly more likely to fail to cleave (Binomial test, p<O.OS) and to arrest at the 4-cell stage (Binomial test, p<O.OS). The number of embryos developing to the blastocyst stage was significantly decreased in embryos derived from sexed sperm as compared to control embryos derived from conventional sperm of the same bull (Binomial test, p<O.OOl). The survival time of embryos derived from sexed semen was significantly shorter as compared to controls (multivariate survival analysis with Cox proportional hazards regression, p<O.OOl). The relative risk for embryos derived from sexed sperm to shrink or fuse cells during development was 1.71 times higher as compared to the conventionally derived embryos. Embryo survival time was significantly bull dependent (Chi-square test, p<O.OOl). With regard to embryonic development, the percentage of apoptotic cells in compact blastocysts was significantly higher as compared to expanding blastocysts hatching blastocysts (multivariate analysis with generalized estimating equation, p<O.OOl). Our results imply that reduced conception rates after sperm sexing are due to decreased developmental capacity of embryos in the 4 cell stage, increased embryonic cell shrinking and cell fusion as well as reduced survival time of blastocysts.

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