Comparison of enzymatic and mechanical methods for the collection of bovine preantral follicles

Harvesting, processing, and evaluation of in vitro-manipulated equine preantral follicles: A review

The mammalian ovary is responsible for essential stages of folliculogenesis and hormonal production, regulating the female physiological functions during the menstrual/estrous cycles. The mare has been considered an attractive model for comparative studies due to the striking similarities shared with women regarding in vivo and in vitro folliculogenesis. The ovarian follicular population in horses contains a large number of oocytes enclosed in preantral follicles that are yet to be explored. Therefore, the in vitro manipulation of equine preantral follicles aims to avoid the process of atresia and promote the development of follicles with competent oocytes. In this regard, after ovarian tissue harvesting, the use of appropriate processing techniques, as well as suitable approaches to evaluating equine preantral follicles and ovarian tissue, are necessary. Although high-quality equine ovarian tissue can be obtained from several sources, some critical aspects, such as the age of the animals, ovarian cyclicity, reproductive phase, and the types of ovarian structures, should be considered. Therefore, this review will focus on providing an update on the most current advances concerning the critical factors able to influence equine preantral follicle quality and quantity. Also, the in vivo strategies used to harvest equine ovarian tissue, the approaches to manipulating ovarian tissue post-harvesting, the techniques for processing ovarian tissue, and the classical approaches used to evaluate preantral follicles will be discussed.

In vitro culture of bovine preantral follicles: a review

Preantral follicles are the majority of the ovarian follicle population and their use as a source of homogeneous oocytes for bovine reproductive biotechnologies could result in a substantial advance in this field. However, while in other species embryos and offspring have been produced, in bovine species the results have been limited to the follicular activation of small (primordial) preantral follicles and formation of early antral follicles from large (secondary) preantral follicles after in vitro culture. Therefore, this review will highlight the basic aspects of bovine folliculogenesis by focusing on preantral follicles, the methods of harvesting preantral follicles, the main results from in vitro follicular culture during the last 20 years, and the potential candidate substances (basic supplements, growth factors, and hormones) for improving the efficiency of in vitro follicle growth.

Isolation and culture of preantral follicles for retrieving oocytes for the embryo production: present status in domestic animals

The development of efficient ovarian preantral follicle (PF) isolation and culture systems provide a large number of oocytes for the manipulation and embryo production. It also helps for understanding the mechanisms of follicle and oocyte development. Isolation and culture protocols for PFs were developed for many domestic species like cattle, buffalo, sheep, goat, pig, horse, camel, dog and cats; however, embryo production from oocytes derived from in vitro grown PFs was reported only in pigs, buffalo, sheep and goat. The rate of oocyte maturation from PFs grown in vitro is low and requires considerable research. This paper presents an overview of isolation and culture systems of PFs that have been developed for domestic species (cattle, buffalo, sheep, goat, pigs, horse, camel, dog and cat) along with the current status of progress achieved in the direction of producing embryos using PFs as the source of oocyte in these species.

Recovery of large preantral follicles from buffalo ovary: Effect of season and corpus luteum

Preantral follicle can be considered as an alternative source of oocyte for in vitro production of embryos. The objective of the present study was to standardize a procedure for the isolation of large preantral follicles (>150-500 microm) from buffalo ovaries and to determine the effect of season and the presence of corpus luteum on the recovery rate of the large preantral follicles. A combined enzymatic cum mechanical approach was adopted to recover the large preantral follicles. In the first experiment, the ovarian cortical pieces were suspended in trypsin (1000-1500 BAEE units for milligrams of solid) and incubated at various temperatures for different periods, i.e. (1) trypsin (1%), 37 degrees C for 10 min; (2) trypsin (1%), 37 degrees C for 10 min + 4 degrees C for 3 h; (3) trypsin (0.5%), 37 degrees C for 20 min; (4) trypsin (0.25%), 37 degrees C for 20 min. Although there was no significant difference (P>0.05) among the different protocols, the first protocol yielded more follicles (3.2, 2.6, 1.8 and 1.5 per ovary, respectively). Hence, the first protocol was selected and used in the second and third experiments. In the second experiment, the effect of season, i.e. peak breeding season (October-March) versus low breeding season (April-September) was evaluated on the recovery rate of the large preantral follicles. The recovery rate of large preantral follicles from the ovaries during the peak breeding season was significantly (P<0.05) greater (9.92+/-0.85 per ovary) than that of the low breeding season (4.95+/-0.27 per ovary). In the third experiment, effect of the presence of corpus luteum on the recovery rate of large preantral follicles was studied. There was a significantly (P<0.05) higher yield of large preantral follicles from the ovaries with corpus luteum (8.05+/-0.88 per ovary) than for the ovaries without corpus luteum (4.57+/-0.43 per ovary). This study confirms that the large preantral follicles can be isolated from buffalo ovaries using a combination of enzymatic cum mechanical methods and that more large preantral follicles can be recovered during the peak breeding season and from the ovaries having corpus luteum.