PARENT SESSION
Follicular Development

THE EFFECT OF ESTROUS CYCLE STAGE ON PREANTRAL FOLLICLE MORPHOLOGY IN THE DOMESTIC DOG.

Durrant, Barbara¹, Amodeo, Dianne¹, Cheng, Alice¹, Zimmerman, Dawn¹, ¹

ABSTRACT- A renewed interest in ovarian function of the domestic dog has been recently stimulated by cloning studies and by the use of the bitch for the development of in vitro maturation and fertilization protocols for wild canids. However, there are few detailed descriptions of ovarian follicles in the bitch (Anderson and Simpson, 1973; Durrant et al., 1998). This study provides morphological data on preantral follicles from prepubertal and anestrous bitches. Prepubertal animals were less than 6 months of age with no significant ovarian structures; anestrous animals were greater than 12 months of age with no ovarian structures other than corpora albicans. Following ovariohysterectomy, half of each ovary from 8 prepubertal and 8 anestrous bitches were fixed in formalin, embedded and sliced into 6 m thin sections. Every tenth section was mounted and stained with Harris′ hematoxylin and then with Shorr stain. Five sections per bitch were analyzed to determine the effects of estrous cycle stage on preantral follicles. The percentage of atretic preantral follicles was greater (p<.05) in the prepubertal (94%) than in the anestrous bitch (88%). The influence of the local ovarian environment was investigated by quantifying the primordial, preantral and antral follicles within a 20X objective field of each preantral follicle examined. The number of primordial follicles in the local environment was not affected by estrous cycle stage. In the anestrous bitch, preantral follicles were surrounded by a greater number of other preantral and antral follicles (both p<.05) than in the prepubertal female. There was no difference in the number of preantral follicles per section between the two estrous cycle stages. But, preantral follicle diameter and oocyte diameter were significantly larger in the anestrus than in the prepubertal female, and there were more granulosa cell layers per follicle in anestrus animals (all p<.05). These data suggest that the proximity of more advanced follicles may stimulate the growth and development of preantral follicles in the anestrous bitch. In vitro maturation may also be enhanced by culturing multiple rather than individual preantral follicles. Comparison of basic follicle dynamics in domestic dogs and exotic canids will determine the suitability of the dog as a model for endangered species.

KEY WORDS: preantral, dog, follicle, morphology