Effects of the reproductive status on morphological oocyte quality and developmental competence of oocytes after in vitro fertilization and somatic cell nuclear transfer in cat

Preservation of female genetic resources in feline species

The development of assisted reproduction techniques (ART) specifically for felids has been propagated for two main reasons: (i) most felids are threatened and faced with extinction in all or part of their native habitats (IUCN Red List of Threatened Species, www.catsg.org), and (ii) the domestic cat (Felis catus) can serve as a research model for the implementation of advanced assisted reproductive techniques (ART) to be applied in exotic cats. Domestic cat ovaries can be freshly obtained from veterinary clinics and are frequently used for research on preservation of genetic resources in feline species. The presented review will summarize recent advances and obstacles in biobanking of female genetic resources and discuss alternative approaches which are under investigation.

Feline embryo development in commercially available human media supplemented with fetal bovine serum

Feline embryo development was examined for 7 days after fertilization using commercially available human media supplemented with 0.3% bovine serum albumin (BSA) or 5% fetal bovine serum (FBS). Cumulus-oocyte complexes were categorized as Grades 1, 2, and 3 according to morphology. Only-One Medium (OM) was used for in vitro culture (IVC) in OM + BSA, OM + FBS, and OM + BSA/FBS, with BSA supplementation for the first 2 days and FBS for the subsequent 5 days. Embryos cultured in Early Culture Medium (1–2 days) and Blastocyst Medium (3–7 days) were defined as EB + BSA and EB + BSA/FBS. The developmental rate until the blastocyst stage of Grade 1 and 2 oocytes cultured in OM + BSA/FBS was higher than for the other groups and was significantly higher than for the OM + BSA and EB + BSA groups (P<0.01). Grade 3 oocytes cultured in OM + BSA/FBS also showed the greatest proportion of blastocyst formation. However, FBS supplementation throughout the IVC period reduced blastocyst number. The percentage of 2 pronuclei after fertilization as well as blastocyst cell number were significantly higher in Grade 1 and 2 than Grade 3 oocytes when cultured in OM + BSA/FBS (P<0.05). These results indicate that commercially available OM supplemented with BSA for the first 2 days of culture and FBS for the subsequent 5 days is suitable for feline embryo development until the blastocyst stage.

Prediction of maturational competence of feline oocytes using supravital staining of cumulus cells by propidium iodide

We examined the relationship between integrity of cumulus cells and nuclear maturation rate after in vitro culture to determine a non-invasive prediction of the maturational competence of feline oocytes. Feline cumulus-oocyte complexes (COCs) were collected from either small (400-800 μm) or large (≥800 μm) follicles. Immediately after collection, cumulus cells were evaluated morphologically (thickness of cumulus cell layers) and stained with propidium iodide (PI), which penetrates only non-viable cells. Cumulus cells without PI staining were judged as having good membrane integrity. After evaluation, COCs were cultured for 30 h and their nuclear maturation rate was determined. The nuclear maturation rate of oocytes derived from large follicles (89.8%) was higher (p < 0.05) than that from small follicles (60.8%). There was no difference in the maturation rate of oocytes from follicles with the same size regardless of cumulus morphology. In contrast, oocytes that had cumulus cells with good membrane integrity showed a higher maturation rate (93.8%) than oocytes with poor cumulus integrity (76.9%) in large follicles (p < 0.05). We conclude that evaluation of membrane integrity of cumulus cells by propidium iodide staining can be used to predict the maturational competence of oocytes.

The effect of ovarian status and follicular diameter on maturational ability of domestic cat oocytes

The objective of this study was to clarify the effect of ovarian status and follicular size on morphological normality and maturational ability of cat oocytes. Ovarian status was classified into inactive, follicular, luteal and prepubertal, and follicles were classified into three groups according to their diameter (400-800, 800-1200 and 1200-2000 µm). In each ovarian status, the number of follicles decreased but the percentage of morphologically normal oocytes increased with the growth of follicles (p<0.05). Only a single follicle that was 1200-2000 µm in diameter was observed in two of the five prepubertal cats. In follicles that were 800-1200 µm in diameter, the percentage of normal oocytes and maturation rate were higher in prepubertal cats than in mature cats (p<0.05). Oocyte diameter tended to increase with the growth of follicles. After oocytes were cultured individually in droplets of maturation medium, the oocyte maturation rate increased with the growth of follicles in each ovarian status (p<0.05). In conclusion, oocytes collected from larger follicles possess higher maturational ability in vitro in sexually mature cats. In prepubertal cats, a higher maturation rate can be obtained from oocytes derived from small follicles compared with in mature cats.