Follicle size and oocyte diameter in relation to developmental competence of buffalo oocytes in vitro

Follicular size, oocyte morphology and diameter were investigated for their possible relationship with in vitro developmental competence of buffalo oocytes. Cumulus oocytes complexes (COCs), aspirated from small (<3 mm), medium (3–8 mm) and large (>8 mm) follicles of normal ovaries and cystic ovarian follicles of abattoir-derived ovaries, were graded for their morphological appearance and were cultured to assess their developmental competence. The influence of cystic follicles on maturational competence of COCs recovered from co-existing follicles of cystic ovaries was studied. The mean diameter of oocytes from follicles of different size were examined, and the influence of oocyte diameter—(i) <126 m; (ii) 127–144 m; (ii) 145–162 m; and (iv) >163 m—on in vitro maturation, cleavage and embryo yield was studied. Results suggested that increased fertilization, cleavage and embryo development were significantly (P<0.05) higher in COCs aspirated from large follicles, followed by medium and small-sized normal follicles, and the presence of cystic follicles had no significant (P<0.05) effect on the maturation competence of the COCs recovered from co-existing follicles. The mean diameter of the buffalo oocyte obtained from normal ovaries was found to be 146.4 m and the rate of blastocyst production in vitro was significantly higher (P<0.05) in oocytes with diameters greater than 145 m. In conclusion, the larger the size of the follicles and oocytes, the greater the developmental competence in vitro of buffalo oocytes.

Fertilisability and developmental ability of mouse oocytes with reduced amounts of cytoplasm

To determine the minimal amount of cytoplasm necessary to support normal development of mouse oocytes, mature unfertilised oocytes were reduced in size into approximately 1/2, 1/4 and 1/8 by removing the cytoplasm, then inseminated. More than 80% of 1/2-size oocyte were fertilised normally and almost all fertilised eggs developed to blastocysts. When transferred to foster females, 31% of the blastocysts developed into normal offspring. In contrast, 1/4- and 1/8-size oocytes, although they were penetrable by spermatozoa and extruded the second polar bodies, could not reach the 2-cell stage. In these oocytes, sperm nuclei did not develop into full-sized pronuclei. These results suggest that an oocyte can develop to full term after losing about half its cytoplasm, but not more.

Varying durations of arrested oocyte development in relation to migration in the African armyworm moth, Spodoptera exempta (Walker) (Lepidoptera: Noctuidae)

The rate of oocyte development in Spodoptera exempta (Walker) was investigated in the laboratory and in the field in Kenya. Stages and rates of development were examined in relation to moth size and timing of mating and oviposition. The stage of oocyte development was established by measuring the widths of the second or third oocyte at the distal end of one ovariole. Data from moths of known age showed that oocytes were partially developed at eclosion and that a linear progression in development occurred up to 30 h after emergence, by which time the oocytes had reached approximately half their mature size. Oocyte development continued unbroken in some moths up to the time of oviposition on the second night after emergence, whilst the remainder arrested oocyte development for a varying number of days. Mating occurred after midnight, but only once the oocytes had reached a certain size, irrespective of whether development was continuous or arrested. In the latter case, this stage was reached immediately after development resumed. Oviposition usually occurred the night after mating, mainly around midnight and with a second peak towards dawn. The dawn peak derived from mature moths which mated and oviposited on the same night. It is suggested that moths arrest oocyte development to minimize wing loading during migration and that, since moths stay in arrested development for varying lengths of time (thought to be genetically regulated), dispersal is greatly enhanced.