Cat presumptive zygotes assessment in relation to their development

The evaluation of oocytes and zygotes, based on their size, shape and morphology, is a valuable tool for predicting subsequent embryo development. While this assessment is non-invasive and made possible with time-lapse monitoring systems, not all the assessment criteria used for zygotes with pale cytoplasm can be used for domestic cat zygotes, which have dark cytoplasm. In this study, feline presumptive zygotes were evaluated for shape, size, and morphology. Measurements were also made of the diameter of the entire zygote, its cytoplasm, and the zona pellucida. Differences in the dataset were assessed using the generalized linear model (GLM) procedure. While there was no relationship between a combination of the tested parameters with the potential for cleavage, blastocyst development, and hatching, the parameters of the shape and size of the entire oocyte, and of the zona pellucida, were related to the development potential. The results presented in this study indicate that the assessment procedure for human zygotes has to be adjusted to be used in the cat model, however the relationship between measurements of the diameter of presumptive feline zygotes and the thickness of zona pellucida with their developmental potential deserves further investigation to optimize assessment of cat presumptive zygotes.