King, W.A., Linares, T., Gustavsson, I. and Bane, A., 1979. A method for preparation of chromosomes from bovine zygotes and blastocysts. Vet. Sci. Commun., 3:51-56.A simple technique for making chromosome preparations from zygotes and early blastocysts is described. The morphological features of blastocysts and total number of cells greatly influence the quality of the preparation. ~qTRODUCTIONThe problems of loss of embryos, poor spreading of chromosomes and over-scattering of cells have been noted to be major handicaps of embryo chromosome analysis with the two basic methods for making preparations, namely squashing and air drying (Fujimoto et al., 1975). In additio~it is often difficult, when working with embryos of a relatively small number of cells, to obtain a reasonable number of cells which have chromosomes in a stage of contraction suitable for analysis. The availability of suitable methods for collection of bovine blastocysts has aided the development of methods for evaluation of karyotypes of early preimplantation embryos and enhanced the possibility of correlating the karyotypes with morphological features of these embryos. In this communication a technique for the preparation of chromosomes from bovine zygotes and early blastocysts is described. Some observations on the quality of preparations obtained from embryos which had normal and abnormal morphological features are presented. MATERIALS AND METHODSSixteen blastocysts and four 2-celled zygotes were used (Table i). The blastocysts were recovered 6 to 7 days after heat (day of heat=0) by a non-surgical

Twenty-four 7 day old bovine embryos were collected from spontaneously ovulating heifers. The embryos were classified into three groups; normal, morphologically deviating G r degenerated. Electron microscopy was used to ascertain the ultrastructural correlates to the phase contrast microscope classification. This study sustains the conclusion that only those embryos classified as normal blastocysts are likely to undergo further development.

The following weak points were identified: 1) Severity assessment is inadequate, 2) use of diagnostic tests is excessive, 3) patients discharged to home with no treatment plan. Opportunities for improvement consisted of: 1) greater availability of peak expiratory flow meters, 2) individualized use of diagnostic tests, and 3) management protocols.

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