The use of laser-assisted hatching in bovine in vitro produced embryos to improve pregnancy rate



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In vitro produced (IVP) embryos not hatching from the zona pellucida (ZP) after transfer is one possible contributing factor of a lower pregnancy rate when compared to in vivo embryos. This study evaluates using a microscope objective mounted laser to cut the ZP prior to transfer into the recipient to assist hatching. The preliminary data evaluated the effect of laser treatment on IVP embryos and subsequent blastomere survival. In six replicates, bovine oocytes were in vitro produced according to the standard laboratory procedures of TransOva Genetics, Sioux Center, IA. On days 5, 6, and 7 of in vitro culture, embryos were randomly divided into 3 groups: no treatment (Control; n=63), sham ZP cut (Sham; n=68), or ZP cut (Cut; n=70). Control embryos were immediately returned to the incubator. Sham embryos were exposed to all conditions as Cut except laser assisted hatching. The XyClone? system was used to treat the Cut group using pulse strength of 90% and pulse length of 600 ?sec. Embryos were returned to culture until day 8 when embryonic development and the percentage of live cells were determined and analyzed with Chi square. The number of developing embryos and the percentage of live cells per embryo showed no significant difference. Mean live cells ranged from 89-96% regardless of day of treatment. The laser assisted hatching effect on IVP embryo viability was evaluated by randomly dividing commercially produced embryos obtained from TransOva Genetics into two groups on day of transfer, Control or Cut. The ZP of treated embryos were cut with the laser using 80% pulse strength and pulse length of 500 ?sec on day 7, immediately prior to transfer into estrous synchronized recipients. Ultrasonagraphy determined pregnancy rates. Thirty day pregnancy rates were 49.2% and 54.1% for Control (n= 189) and Cut (n=148) embryos, respectively, and were not statistically different (p > 0.05). However, 60 day Control pregnancy rate was 45.7% (n= 166) and the Cut group rate was 57.7% (n= 123) revealing a statistical difference (p < 0.05). These results demonstrate that the XyClone? system assisted hatching can improve 60 day pregnancy rates for IVP embryos by approximately 11 %.