Nucleolar ultrastructural changes occurring in vivo in bovine oocytes during follicular growth were analyzed by electron microscopy. The rates of in vitro incorporation of 3H‐uridine by oocytes of the same size class were evaluated by autoradiography. One to two large fibrillogranular, vacuolated nucleoli were present in oocytes from small to medium antral follicles 0.5–3 mm in diameter. These oocytes showed intense hnRNA and rRNA synthesis. The homogeneous, agranular nucleoli in oocytes from follicles 3–4 mm in diameter were composed of a compact fibrillar material. This morphological change was accompanied by an impairment of nucleolar transcriptional activity as well as by a decrease in hnRNA synthesis.

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Aims: To determine susceptibility of Clostridium perfringens strains CCM 4435 T and CNCTC 5459 to C 2 -C 18 fatty acids, and evaluate influence of pH in cultures grown on glucose. Straw particles were added to cultures to simulate the presence of solid phase of the digestive tract milieu. Methods and Results: Antimicrobial activity of fatty acids was expressed as a concentration at which only 50% of the initial glucose was utilized. Lauric acid showed the highest antimicrobial activity, followed by myristic, capric, oleic and caprylic acid. Only strain CNCTC 5459 was susceptible to linoleic acid. Neither caproic acid and acids with a shorter carbon chain nor palmitic and stearic acid influenced substrate utilization. The antimicrobial activity of myristic, oleic and linoleic acid decreased when clostridia were grown in the presence of straw particles. In cultures of both strains treated with capric and lauric acid at pH 5AE0-5AE3, the number of viable cells was <10 2 ml )1 . Only lauric acid reduced number of viable cells of both strains below 10 2 ml )1 at pH > 6. Transmission electron microscopy revealed separation of inner and outer membranes and cytoplasma disorganization in cells treated with lauric acid. Conclusions: Lauric acid had the highest activity towards C. perfringens among fatty acid tested. Its activity was not influenced by the presence of solid particles and did not cease at pH > 6. Significance and Impact of the Study: Lauric acid might be a means for control of clostridial infections in farm animals.

The aim of this study was to examine the temporal sensitivity of bovine embryos to culture environment after fertilization to determine which period, if any, is most critical in determining blastocyst quality. Bovine zygotes produced in vitro were divided into six groups and cultured either in vitro (in synthetic oviductal fluid, SOF), in vivo (in the ewe oviduct) or in a combination of both systems. Development to the blastocyst stage, the ability of the blastocysts to withstand cryopreservation and the relative abundance of several gene transcripts were examined. Culture in SOF for either 2 or 4 days, followed by subsequent culture in the ewe oviduct, resulted in a significantly lower yield of blastocysts than did all other methods, the effect being most marked in embryos that were cultured in SOF for 4 days. In contrast, culture in vivo for the first 2 or 4 days after fertilization followed by culture in vitro did not have such a marked effect on blastocyst development. Blastocysts produced after culture in the oviduct for 6 days had the highest rates of survival over 72 h after warming (100% survival at 24 h; > 95% survival at 72 h). The embryos that spent the last 4 days of culture in vivo also had relatively high rates of survival (100% at 24 h, 73.7% at 72 h). Blastocysts produced entirely in SOF had very low rates of survival after vitrification, with < 40% viable at 24 h and < 20% survival at 72 h. Blastocysts derived from embryos that spent the first 2 days in vivo and the last 4 days in vitro had the lowest rates of survival (6.7%), whereas those that spent the last 2 days only in SOF had intermediate rates of survival (40.6%). These differences were reflected in the relative abundance of transcripts for the Bax gene.

The onset of RNA synthesis in developing early pig embryos from 1-cell to 8-cell and morula stages was studied using high-resolution autoradiography of (5-3H)uridine incorporation. No transcriptional activity was detected in nuclei of 1- and 2-cell stage embryos with this technique. In these embryos nucleolus-like bodies (NLB) consist of sharply delineated, round, electron dense fibrillar masses. In the 4-cell stage embryos, the first uridine-3H incorporation in the nucleoplasm was detected and localized mainly near the regions of condensed chromatin. The first signs of reticulation and chromatin association were observed at the periphery of NLBs. In the next cell cycle (5- to 8-cell embryos) uridine-3H labelling was detected in the nucleoplasm and nucleoli. In these embryos, nucleoli consist of a central dense fibrillar mass without any transcriptional activity and fibrillo-granular cortex over which label was localized. The degree of functional restructure of nucleoli was variable within one blastomere or among different blastomeres, some nucleoli being more reticulated and showing more transcriptional activity than others. Fully developed nucleoli were present in early morulae. Electron dense unidentified structures described here as small dense round-shaped bodies (RDB) often surrounded by blocks of large chromatin granules were observed in intact 2-cell and alpha-amanitin treated 4-cell stage embryos. These structures did not show any transcriptional activity.