Early indications of breed differences for cryopreservation of embryos in cattle
Cryopreservation is considered state of the art procedure to store embryos in most industry settings. However, some species (i.e. humans) do not survive the freezing/thawing process well; additionally, some breeds within successful species do not survive this process well either (i.e. Jersey cattle); therefore, more research is needed to perfect the process. While the cryopreservation process assumes that water is conserved across species, there is no proof this assumption is correct. Thus, any significant change in the chemical constituents of embryos could identify the problems with that species’ or breed’s freezing and thawing success rates. Therefore, the objective of this study was to determine if embryos from different breeds within the same species demonstrate any significantly different in chemical compositions.
In these experiments, a unique modified specific gravity chamber was created in order to estimate the weight of preimplantation embryos from varying cattle breeds. Once the system had been standardized with beads of know size and weight, day six embryos from Jersey and beef cattle were processed through the system and the rate of descent plotted against the standard curve to estimate embryo weight. Additionally, embryos from both groups were fixed and sectioned for electron microscopy, and random micrographs used to quantify lipid content . Data analysis was performed on SPSS version 12 with an intra-assay CV being run between standard curves and a Student’s T-Test for lipid quantification.
Embryos of each breed were amazingly consistent in time of descent. However, the estimated weight of Jersey embryos appeared to be significantly lighter weight than beef cattle embryos (P < .001). Additionally, electron microscopy suggests the Jersey embryos contain greater amounts of lipid droplets at the same stage of development (P < .001).
These data represent the first true estimation of embryo weight at this stage of development. Moreover, the data suggest these differences may be due solely to the number lipid droplets found within the cells. Further study will be needed to determine if knowing lipid content of embryos of individual breeds or species will allow improvement in cryopreservation success for that group.