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Peripheral plasma levels of progesterone1) and 15-keto-13,14-dihydroprostaglandin F2\g=a\ were measured during the normal oestrous cycle in three heifers. Before the experiment the animals received an infusion each of different amounts of prostaglandin F2\g=a\ to estimate the conversion of this compound into the main plasma metabolite, 15-keto-13,14-dihydroPGF2a. The experimental period was initiated by heat synchronization with 25 mg prostaglandin F2a given intramuscularly. Daily blood samples were collected from the jugular vein until day 14 of the oestrous cycle and subsequently every third hour until heat occurred. During this heat the three heifers were mated, and blood samples were collected in the same way during the following cycle and over the next expected heat. Pregnancy occurred in one of the animals. High levels of 15-keto-13,14\x=req-\ I) The following trivial names are used:Progesterone: 4-pregnene-3,20-dione.Prostaglandin F2(( (PGF2r/): 9ot,lla,15-trihydroxyprosta-5,13-dienoic acid. 15-keto-13,14-dihydro-prostaglandin F2a: 9a,lla-dihydroxy-15-ketoprost-5-enoic acid.

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

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