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R. J. AITKEN, J. BURTON, J. HAWKINS, R. KERR-WILSON, R. V. SHORT and D. H. STEVEN

Summary.

The ultrastructure of four roe-deer blastocysts at different stages of embryonic development were studied. During delayed implantation, the outer surface of the trophoblast possessed numerous microvilli and periodic invaginations or caveolae. There was a marked lack of organelles such as mitochondria or endoplasmic reticulum in the cytoplasm of the trophoblast cells, though many lipid droplets, granular inclusions and a lamina of fine fibrillae were present. Elongation of the blastocyst was associated with a decrease in the size and number of the microvilli, the disappearance of lipid droplets and granular inclusions, a reduction in the amount of fibrillar material and a dramatic increase in the development of mitochondria, granular endoplasmic reticulum, ribosomes and Golgi apparatus.

The histology of the ovaries and uterus was studied in thirty-one roe deer. No prominent changes occurred in the ovaries at any stage of development; all ovaries possessed active CL and showed signs of follicular growth and atresia. Changes in the degree of mitotic activity, epithelial cell height, endometrial vascularity and stromal oedema were observed in the uterus throughout the period of delayed implantation and during the phase of rapid embryonic growth. Elongation of the embryo was associated with a marked decline in the height of the glandular epithelium and an increase in endometrial vascularity.

The most important ultrastructural changes in the uteri of six roe deer were observed in the endometrial glands. Delayed implantation was associated with the accumulation of numerous supranuclear vesicles derived from the Golgi apparatus, while the resumption of embryonic growth was correlated with their sudden disappearance. When elongation had been completed, there was a sudden decrease in the cellular activity of these endometrial glands.

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D. Pomp, D. E. Cowley, E. J. Eisen, W. R. Atchley and D. Hawkins-Brown

Summary. Reciprocal embryo transfers amongst two inbred strains (C3HeB/FeJ and SWR/J) and their F1 cross (C3SWF1) were used to examine donor and recipient genotype and heterosis effects on survival and prenatal growth of mouse embryos. Among inbred strains, significant recipient genotype effects were detected for both embryo survival (P < 0·01) and prenatal growth (P < 0·05), while no donor genotype effects were observed. The recipient effect on overall embryo survival was due to a higher proportion of C3H recipients maintaining pregnancy to term than SWR recipients (P < 0·01), rather than survival within litters. Irrespective of their own genotype, embryos developing in C3H uteri achieved larger body weights (P < 0·01) and longer tail lengths (P < 0·05) at birth than did embryos developing in SWR uteri. Recipient heterosis was not significant, while donor heterosis was significant for prenatal growth traits (P < 0·001).

Keywords: embryo survival; uterus; maternal effects; genetics; mice

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J A McGlothlin, G D Lester, P J Hansen, M Thomas, L Pablo, D L Hawkins and M M LeBlanc

An experimental model of ascending placentitis was developed in the mare to characterize the uterine myoelectrical pattern in late gestation and determine how ascending placentitis altered this pattern. In experiment 1, myometrial electrical activity was analyzed during the early morning, late morning and evening hours in four mares in the last 15 days of gestation to identify patterns of activity. In experiment 2, nine mares received intra-cervical inoculations of Streptococcus equi subspecies zooepidemicus. Myoelectrical activity in the early morning and evening hours in these mares was compared with four control mares. In experiment 1, the number of spike burst clusters >30 s was greater in the evening than in the late morning hours (P < 0.04). Spike burst activity (number × duration) of mares in experiment 1 was similar during day and night recordings until the last 6 days of gestation when it gradually increased each evening until parturition (P < 0.05). In experiment 2, control mares experienced a gradual increase in the number of small spike burst clusters in the last 6 days (P = 0.008) and an increase in large and small spike burst clusters in the evening hours in the last 4 days of gestation (P = 0.03). Mares with experimentally induced placentitis never exhibited a rise in spike burst clusters but had an increase in the mean duration and activity index of large spike burst clusters in the 4 days before parturition (P < 0.04). In conclusion, control mares had a progressive, reversible rise in myoelectrical activity at night in the week preceding parturition. This was not observed in mares with experimentally induced placentitis. They exhibited an increase in the intensity and duration of large spike burst clusters possibly in response to local inflammation.